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A ____ is a structure that allows repeated execution of a block of statements.

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This chapter shows you how to structure the flow of control through a PL/SQL program. You learn how statements are connected by simple but powerful control structures that have a single entry and exit point. Collectively, these structures can handle any situation. And, their proper use leads naturally to a well-structured program.

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Major Topics

Overview

According to the structure theorem, any computer program can be written using the basic control structures shown in . They can be combined in any way necessary to deal with a given problem.

Figure 3-1 Control Structures

A ____ is a structure that allows repeated execution of a block of statements.

The selection structure tests a condition, then executes one sequence of statements instead of another, depending on whether the condition is true or false. A condition is any variable or expression that returns a Boolean value (

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
5 or 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
6). The iteration structure executes a sequence of statements repeatedly as long as a condition holds true. The sequence structure simply executes a sequence of statements in the order in which they occur.

Conditional Control: IF Statements

Often, it is necessary to take alternative actions depending on circumstances. The 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement lets you execute a sequence of statements conditionally. That is, whether the sequence is executed or not depends on the value of a condition. There are three forms of 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statements: 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
9, 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
0, and 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
1.

IF-THEN

The simplest form of 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement associates a condition with a sequence of statements enclosed by the keywords 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
3 and 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
4 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 (not 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
6), as follows:

IF condition THEN
   sequence_of_statements;
END IF;

The sequence of statements is executed only if the condition yields 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
5. If the condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
6 or 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9, the 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement does nothing. In either case, control passes to the next statement. An example follows:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;

You might want to place brief 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statements on a single line, as in

IF x > y THEN high := x; END IF;

IF-THEN-ELSE

The second form of 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement adds the keyword 
BEGIN
   ...
   IF sales > 50000 THEN
      bonus := 1500;
   ELSIF sales > 35000 THEN
      bonus := 500;
   ELSE
      bonus := 100;
   END IF;
   INSERT INTO payroll VALUES (emp_id, bonus, ...);
END;
3 followed by an alternative sequence of statements, as follows:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;

The sequence of statements in the 

BEGIN
   ...
   IF sales > 50000 THEN
      bonus := 1500;
   ELSIF sales > 35000 THEN
      bonus := 500;
   ELSE
      bonus := 100;
   END IF;
   INSERT INTO payroll VALUES (emp_id, bonus, ...);
END;
3 clause is executed only if the condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
6 or 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9. Thus, the 
BEGIN
   ...
   IF sales > 50000 THEN
      bonus := 1500;
   ELSIF sales > 35000 THEN
      bonus := 500;
   ELSE
      bonus := 100;
   END IF;
   INSERT INTO payroll VALUES (emp_id, bonus, ...);
END;
3 clause ensures that a sequence of statements is executed. In the following example, the first or second 
BEGIN
   ...
   IF sales > 50000 THEN
      bonus := 1500;
   ELSIF sales > 35000 THEN
      bonus := 500;
   ELSE
      bonus := 100;
   END IF;
   INSERT INTO payroll VALUES (emp_id, bonus, ...);
END;
8 statement is executed when the condition is true or false, respectively:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;

The 

IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
3 and 
BEGIN
   ...
   IF sales > 50000 THEN
      bonus := 1500;
   ELSIF sales > 35000 THEN
      bonus := 500;
   ELSE
      bonus := 100;
   END IF;
   INSERT INTO payroll VALUES (emp_id, bonus, ...);
END;
3 clauses can include 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statements. That is, 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statements can be nested, as the following example shows:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;

IF-THEN-ELSIF

Sometimes you want to select an action from several mutually exclusive alternatives. The third form of 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement uses the keyword 
DECLARE
   ...
   overdrawn  BOOLEAN;
BEGIN
   ...
   IF new_balance < minimum_balance THEN
      overdrawn := TRUE;
   ELSE
      overdrawn := FALSE;
   END IF;
   ...
   IF overdrawn = TRUE THEN
      RAISE insufficient_funds;
   END IF;
END;
4 (not 
DECLARE
   ...
   overdrawn  BOOLEAN;
BEGIN
   ...
   IF new_balance < minimum_balance THEN
      overdrawn := TRUE;
   ELSE
      overdrawn := FALSE;
   END IF;
   ...
   IF overdrawn = TRUE THEN
      RAISE insufficient_funds;
   END IF;
END;
5) to introduce additional conditions, as follows:

IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;

If the first condition yields 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
6 or 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9, the 
DECLARE
   ...
   overdrawn  BOOLEAN;
BEGIN
   ...
   IF new_balance < minimum_balance THEN
      overdrawn := TRUE;
   ELSE
      overdrawn := FALSE;
   END IF;
   ...
   IF overdrawn = TRUE THEN
      RAISE insufficient_funds;
   END IF;
END;
4 clause tests another condition. An 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement can have any number of 
DECLARE
   ...
   overdrawn  BOOLEAN;
BEGIN
   ...
   IF new_balance < minimum_balance THEN
      overdrawn := TRUE;
   ELSE
      overdrawn := FALSE;
   END IF;
   ...
   IF overdrawn = TRUE THEN
      RAISE insufficient_funds;
   END IF;
END;
4 clauses; the final 
BEGIN
   ...
   IF sales > 50000 THEN
      bonus := 1500;
   ELSIF sales > 35000 THEN
      bonus := 500;
   ELSE
      bonus := 100;
   END IF;
   INSERT INTO payroll VALUES (emp_id, bonus, ...);
END;
3 clause is optional. Conditions are evaluated one by one from top to bottom. If any condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
5, its associated sequence of statements is executed and control passes to the next statement. If all conditions yield 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
6 or 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9, the sequence in the 
BEGIN
   ...
   IF sales > 50000 THEN
      bonus := 1500;
   ELSIF sales > 35000 THEN
      bonus := 500;
   ELSE
      bonus := 100;
   END IF;
   INSERT INTO payroll VALUES (emp_id, bonus, ...);
END;
3 clause is executed. Consider the following example:

BEGIN
   ...
   IF sales > 50000 THEN
      bonus := 1500;
   ELSIF sales > 35000 THEN
      bonus := 500;
   ELSE
      bonus := 100;
   END IF;
   INSERT INTO payroll VALUES (emp_id, bonus, ...);
END;

If the value of 

overdrawn := new_balance < minimum_balance;
6 is more than 50000, the first and second conditions are true. Nevertheless, 
overdrawn := new_balance < minimum_balance;
7 is assigned the proper value of 1500 because the second condition is never tested. When the first condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
5, its associated statement is executed and control passes to the 
overdrawn := new_balance < minimum_balance;
9 statement.

Guidelines

Avoid clumsy 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statements like those in the following example:

DECLARE
   ...
   overdrawn  BOOLEAN;
BEGIN
   ...
   IF new_balance < minimum_balance THEN
      overdrawn := TRUE;
   ELSE
      overdrawn := FALSE;
   END IF;
   ...
   IF overdrawn = TRUE THEN
      RAISE insufficient_funds;
   END IF;
END;

This code disregards two useful facts. First, the value of a Boolean expression can be assigned directly to a Boolean variable. So, you can replace the first 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement with a simple assignment, as follows:

overdrawn := new_balance < minimum_balance;

Second, a Boolean variable is itself either true or false. So, you can simplify the condition in the second 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement, as follows:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
0

When possible, use the 

DECLARE
   ...
   overdrawn  BOOLEAN;
BEGIN
   ...
   IF new_balance < minimum_balance THEN
      overdrawn := TRUE;
   ELSE
      overdrawn := FALSE;
   END IF;
   ...
   IF overdrawn = TRUE THEN
      RAISE insufficient_funds;
   END IF;
END;
4 clause instead of nested 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statements. That way, your code will be easier to read and understand. Compare the following 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statements:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
1

These statements are logically equivalent, but the first statement obscures the flow of logic, whereas the second statement reveals it.

Iterative Control: LOOP and EXIT Statements

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 statements let you execute a sequence of statements multiple times. There are three forms of 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 statements: 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06, 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
09, and 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
10.

LOOP

The simplest form of 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 statement is the basic (or infinite) loop, which encloses a sequence of statements between the keywords 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 and 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
4 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06, as follows:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
2

With each iteration of the loop, the sequence of statements is executed, then control resumes at the top of the loop. If further processing is undesirable or impossible, you can use an 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement to complete the loop. You can place one or more 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statements anywhere inside a loop, but nowhere outside a loop. There are two forms of 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statements: 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 and 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
19.

EXIT

The 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement forces a loop to complete unconditionally. When an 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement is encountered, the loop completes immediately and control passes to the next statement. An example follows:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
3

The next example shows that you cannot use the 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement to complete a PL/SQL block:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
4

Remember, the 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement must be placed inside a loop. To complete a PL/SQL block before its normal end is reached, you can use the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
24 statement. For more information, see .

EXIT-WHEN

The 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
19 statement allows a loop to complete conditionally. When the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement is encountered, the condition in the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
27 clause is evaluated. If the condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
5, the loop completes and control passes to the next statement after the loop. An example follows:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
5

Until the condition yields 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
5, the loop cannot complete. So, statements within the loop must change the value of the condition. In the last example, if the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
30 statement returns a row, the condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
6. When the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
30 statement fails to return a row, the condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
5, the loop completes, and control passes to the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
34 statement.

The 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
19 statement replaces a simple 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement. For example, compare the following statements:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
6

These statements are logically equivalent, but the 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
19 statement is easier to read and understand.

Loop Labels

Like PL/SQL blocks, loops can be labeled. The label, an undeclared identifier enclosed by double angle brackets, must appear at the beginning of the 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 statement, as follows:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
7

Optionally, the label name can also appear at the end of the 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 statement, as the following example shows:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
8

When you nest labeled loops, you can use ending label names to improve readability.

With either form of 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement, you can complete not only the current loop, but any enclosing loop. Simply label the enclosing loop that you want to complete. Then, use the label in an 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement, as follows:

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
9

Every enclosing loop up to and including the labeled loop is exited.

WHILE-LOOP

The 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
09 statement associates a condition with a sequence of statements enclosed by the keywords 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 and 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
4 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06, as follows:

IF x > y THEN high := x; END IF;
0

Before each iteration of the loop, the condition is evaluated. If the condition yields 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
5, the sequence of statements is executed, then control resumes at the top of the loop. If the condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
6 or 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9, the loop is bypassed and control passes to the next statement. An example follows:

IF x > y THEN high := x; END IF;
1

The number of iterations depends on the condition and is unknown until the loop completes. Since the condition is tested at the top of the loop, the sequence might execute zero times. In the last example, if the initial value of 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
49 is greater than 25000, the condition yields 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
6 and the loop is bypassed.

Some languages have a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
52 or 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
53 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
52 structure, which tests the condition at the bottom of the loop instead of at the top. Therefore, the sequence of statements is executed at least once. PL/SQL has no such structure, but you can easily build one, as follows:

IF x > y THEN high := x; END IF;
2

To ensure that a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
55 loop executes at least once, use an initialized Boolean variable in the condition, as follows:

IF x > y THEN high := x; END IF;
3

A statement inside the loop must assign a new value to the Boolean variable. Otherwise, you have an infinite loop. For example, the following 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 statements are logically equivalent:

IF x > y THEN high := x; END IF;
4

FOR-LOOP

Whereas the number of iterations through a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
55 loop is unknown until the loop completes, the number of iterations through a 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loop is known before the loop is entered. 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loops iterate over a specified range of integers. (Cursor 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loops, which iterate over the result set of a cursor, are discussed in .) The range is part of an iteration scheme, which is enclosed by the keywords 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 and 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06. A double dot (
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
63) serves as the range operator. The syntax follows:

IF x > y THEN high := x; END IF;
5

The range is evaluated when the 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loop is first entered and is never re-evaluated.

As the next example shows, the sequence of statements is executed once for each integer in the range. After each iteration, the loop counter is incremented.

IF x > y THEN high := x; END IF;
6

The following example shows that if the lower bound equals the higher bound, the sequence of statements is executed once:

IF x > y THEN high := x; END IF;
7

By default, iteration proceeds upward from the lower bound to the higher bound. However, if you use the keyword 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
65, iteration proceeds downward from the higher bound to the lower bound, as the example below shows. After each iteration, the loop counter is decremented.

IF x > y THEN high := x; END IF;
8

Nevertheless, you write the range bounds in ascending (not descending) order.

Inside a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loop, the loop counter can be referenced like a constant. So, the loop counter can appear in expressions but cannot be assigned values, as the following example shows:

IF x > y THEN high := x; END IF;
9

Iteration Schemes

The bounds of a loop range can be literals, variables, or expressions but must evaluate to integers. For example, the following iteration schemes are legal:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
0

As you can see, the lower bound need not be 1. However, the loop counter increment (or decrement) must be 1. Some languages provide a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
67 clause, which lets you specify a different increment. An example written in BASIC follows:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
1

PL/SQL has no such structure, but you can easily build one. Consider the following example:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
2

This loop is logically equivalent to the previous BASIC loop. Within the sequence of statements, the loop counter has only the values 5, 10, and 15.

You might prefer the less elegant but more efficient method shown in the example below. Within the sequence of statements, each reference to the loop counter is multiplied by the increment.

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
3

Dynamic Ranges

PL/SQL lets you determine the loop range dynamically at run time, as the following example shows:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
4

The value of 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
68 is unknown at compile time; the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
69 statement returns the value at run time.

What happens if the lower bound of a loop range evaluates to a larger integer than the upper bound? As the next example shows, the sequence of statements within the loop is not executed and control passes to the next statement:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
5

Scope Rules

The loop counter is defined only within the loop. You cannot reference it outside the loop. After the loop is exited, the loop counter is undefined, as the following example shows:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
6

You need not explicitly declare the loop counter because it is implicitly declared as a local variable of type 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
70. The next example shows that the local declaration hides any global declaration:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
7

To reference the global variable in this example, you must use a label and dot notation, as follows:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
8

The same scope rules apply to nested 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loops. Consider the example below. Both loop counters have the same name. So, to reference the outer loop counter from the inner loop, you must use a label and dot notation, as follows:

IF condition THEN
   sequence_of_statements1;
ELSE
   sequence_of_statements2;
END IF;
9

Using the EXIT Statement

The 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement allows a 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loop to complete prematurely. For example, the following loop normally executes ten times, but as soon as the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
30 statement fails to return a row, the loop completes no matter how many times it has executed:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
0

Suppose you must exit from a nested 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loop prematurely. You can complete not only the current loop, but any enclosing loop. Simply label the enclosing loop that you want to complete. Then, use the label in an 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
15 statement to specify which 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
58 loop to exit, as follows:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
1

Sequential Control: GOTO and NULL Statements

Unlike the 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 and 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 statements, the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 and 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statements are not crucial to PL/SQL programming. The structure of PL/SQL is such that the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement is seldom needed. Occasionally, it can simplify logic enough to warrant its use. The 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement can make the meaning and action of conditional statements clear and so improve readability.

Overuse of 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statements can result in complex, unstructured code (sometimes called spaghetti code) that is hard to understand and maintain. So, use 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statements sparingly. For example, to branch from a deeply nested structure to an error-handling routine, raise an exception rather than use a 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement.

GOTO Statement

The 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement branches to a label unconditionally. The label must be unique within its scope and must precede an executable statement or a PL/SQL block. When executed, the 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement transfers control to the labeled statement or block. In the following example, you go to an executable statement farther down in a sequence of statements:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
2

In the next example, you go to a PL/SQL block farther up in a sequence of statements:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
3

The label 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
89in the following example is illegal because it does not precede an executable statement:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
4

To debug the last example, simply add the 

IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement, as follows:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
5

As the following example shows, a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement can branch to an enclosing block from the current block:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
6

The 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement branches to the first enclosing block in which the referenced label appears.

Restrictions

Some possible destinations of a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement are illegal. Specifically, a 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement cannot branch into an 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement, 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
06 statement, or sub-block. For example, the following 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement is illegal:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
7

Also, a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement cannot branch from one 
IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement clause to another, as the following example shows:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
8

The next example shows that a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement cannot branch from an enclosing block into a sub-block:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   UPDATE accounts SET balance = balance - debit WHERE ...
END IF;
9

Also, a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement cannot branch out of a subprogram, as the following example shows:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
0

Finally, a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement cannot branch from an exception handler into the current block. For example, the following 
IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement is illegal:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
1

However, a 

IF sales > quota THEN
   compute_bonus(empid);
   UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id;
END IF;
80 statement can branch from an exception handler into an enclosing block.

NULL Statement

The 

IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement explicitly specifies inaction; it does nothing other than pass control to the next statement. It can, however, improve readability. In a construct allowing alternative actions, the 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement serves as a placeholder. It tells readers that the associated alternative has not been overlooked, but that indeed no action is necessary. In the following example, the 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement shows that no action is taken for unnamed exceptions:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
2

Each clause in an 

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
7 statement must contain at least one executable statement. The 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement meets this requirement. So, you can use the 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement in clauses that correspond to circumstances in which no action is taken. In the following example, the 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement emphasizes that only top-rated employees receive bonuses:

IF trans_type = 'CR' THEN
   UPDATE accounts SET balance = balance + credit WHERE ...
ELSE
   IF new_balance >= minimum_balance THEN
      UPDATE accounts SET balance = balance - debit WHERE ...
   ELSE
      RAISE insufficient_funds;
   END IF;
END IF;
3

Also, the 

IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement is a handy way to create stubs when designing applications from the top down. A stub is dummy subprogram that allows you to defer the definition of a procedure or function until you test and debug the main program. In the following example, the 
IF condition1 THEN
   sequence_of_statements1;
ELSIF condition2 THEN
   sequence_of_statements2;
ELSE
   sequence_of_statements3;
END IF;
9 statement meets the requirement that at least one statement must appear in the executable part of a subprogram:

What is a structure that allows repeated execution of a block of statements?

A loop is a structure that allows repeated execution of a block of statements. Within a looping structure, a Boolean expression is evaluated.

Which structure causes a statement or set of statements to execute repeatedly quizlet?

More commonly known as a loop, a repetition structure causes a statement or set of statements to execute repeatedly as many times as necessary. What is a condition-controlled loop? A condition-controlled loop causes a statement or set of statements to repeat as long as a condition is true.

What is the term for one execution of a loop?

A single execution of the loop body is called an iteration. The loop in the example above makes three iterations.

What is an indefinite loop?

An indefinite loop is a loop that waits for some condition to become true. In general, it's not obvious how many iterations it takes. For example, you might be looking for the first number that is divisible by 2, 3, 5, 7, and 11.

____ structure repeated execution block statements

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