4 PL/SQL Control Statements

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PL/SQL has three categories of control statements:

• Conditional selection statements, which run different statements for different data values.

  The conditional selection statements are IF and and CASE.

• Loop statements, which run the same statements with a series of different data values.

  The loop statements are the basic LOOP, FOR LOOP, and WHILE LOOP.

  The EXIT statement transfers control to the end of a loop. The CONTINUE statement exits the current iteration of a loop and transfers control to the next iteration. Both EXIT and CONTINUE have an optional WHEN clause, where you can specify a condition.

• Sequential control statements, which are not crucial to PL/SQL programming.

  The sequential control statements are GOTO, which goes to a specified statement, and NULL, which does nothing.

Topics

• Conditional Selection Statements

• LOOP Statements

• Sequential Control Statements

Conditional Selection Statements

The conditional selection statements, IF and CASE, run different statements for different data values.

The IF statement either runs or skips a sequence of one or more statements, depending on a condition. The IF statement has these forms:

• IF THEN

• IF THEN ELSE

• IF THEN ELSIF

The CASE statement chooses from a sequence of conditions, and runs the corresponding statement. The CASE statement has these forms:

• Simple, which evaluates a single expression and compares it to several potential values.

• Searched, which evaluates multiple conditions and chooses the first one that is true.

The CASE statement is appropriate when a different action is to be taken for each alternative.

Topics

• IF THEN Statement

• IF THEN ELSE Statement

• IF THEN ELSIF Statement

• Simple CASE Statement

• Searched CASE Statement

IF THEN Statement

The IF THEN statement has this structure:

IF condition THEN statements END IF;

If the condition is true, the statements run; otherwise, the IF statement does nothing. (For complete syntax, see "IF Statement".)

In Example 4-1, the statements between THEN and END IF run if and only if the value of sales is greater than quota+200.

Example 4-1 IF THEN Statement

DECLARE PROCEDURE p ( sales NUMBER, quota NUMBER, emp_id NUMBER ) IS bonus NUMBER := 0; updated VARCHAR2(3) := 'No'; BEGIN IF sales > (quota + 200) THEN bonus := (sales - quota)/4; UPDATE employees SET salary = salary + bonus WHERE employee_id = emp_id; updated := 'Yes'; END IF; DBMS_OUTPUT.PUT_LINE ( 'Table updated? ' || updated || ', ' || 'bonus = ' || bonus || '.' ); END p; BEGIN p(10100, 10000, 120); p(10500, 10000, 121); END; /

Result:

Table updated? No, bonus = 0. Table updated? Yes, bonus = 125.

Tip:

Avoid clumsy IF statements such as: IF new_balance < minimum_balance THEN overdrawn := TRUE; ELSE overdrawn := FALSE; END IF;

Instead, assign the value of the BOOLEAN expression directly to a BOOLEAN variable:

overdrawn := new_balance < minimum_balance;

A BOOLEAN variable is either TRUE, FALSE, or NULL. Do not write:

IF overdrawn = TRUE THEN RAISE insufficient_funds; END IF;

Instead, write:

IF overdrawn THEN RAISE insufficient_funds; END IF;

IF THEN ELSE Statement

The IF THEN ELSE statement has this structure:

IF condition THEN statements ELSE else_statements END IF;

If the value of condition is true, the statements run; otherwise, the else_statements run. (For complete syntax, see "IF Statement".)

In Example 4-2, the statement between THEN and ELSE runs if and only if the value of sales is greater than quota+200; otherwise, the statement between ELSE and END IF runs.

Example 4-2 IF THEN ELSE Statement

DECLARE PROCEDURE p ( sales NUMBER, quota NUMBER, emp_id NUMBER ) IS bonus NUMBER := 0; BEGIN IF sales > (quota + 200) THEN bonus := (sales - quota)/4; ELSE bonus := 50; END IF; DBMS_OUTPUT.PUT_LINE('bonus = ' || bonus); UPDATE employees SET salary = salary + bonus WHERE employee_id = emp_id; END p; BEGIN p(10100, 10000, 120); p(10500, 10000, 121); END; /

Result:

bonus = 50 bonus = 125

IF statements can be nested, as in Example 4-3.

Example 4-3 Nested IF THEN ELSE Statements

DECLARE PROCEDURE p ( sales NUMBER, quota NUMBER, emp_id NUMBER ) IS bonus NUMBER := 0; BEGIN IF sales > (quota + 200) THEN bonus := (sales - quota)/4; ELSE IF sales > quota THEN bonus := 50; ELSE bonus := 0; END IF; END IF; DBMS_OUTPUT.PUT_LINE('bonus = ' || bonus); UPDATE employees SET salary = salary + bonus WHERE employee_id = emp_id; END p; BEGIN p(10100, 10000, 120); p(10500, 10000, 121); p(9500, 10000, 122); END; /

Result:

bonus = 50 bonus = 125 bonus = 0

IF THEN ELSIF Statement

The IF THEN ELSIF statement has this structure:

IF condition_1 THEN statements_1 ELSIF condition_2 THEN statements_2 [ ELSIF condition_3 THEN statements_3 ]... [ ELSE else_statements ] END IF;

The IF THEN ELSIF statement runs the first statements for which condition is true. Remaining conditions are not evaluated. If no condition is true, the else_statements run, if they exist; otherwise, the IF THEN ELSIF statement does nothing. (For complete syntax, see "IF Statement".)

In Example 4-4, when the value of sales is larger than 50000, both the first and second conditions are true. However, because the first condition is true, bonus is assigned the value 1500, and the second condition is never tested. After bonus is assigned the value 1500, control passes to the DBMS_OUTPUT.PUT_LINE invocation.

Example 4-4 IF THEN ELSIF Statement

DECLARE PROCEDURE p (sales NUMBER) IS bonus NUMBER := 0; BEGIN IF sales > 50000 THEN bonus := 1500; ELSIF sales > 35000 THEN bonus := 500; ELSE bonus := 100; END IF; DBMS_OUTPUT.PUT_LINE ( 'Sales = ' || sales || ', bonus = ' || bonus || '.' ); END p; BEGIN p(55000); p(40000); p(30000); END; /

Result:

Sales = 55000, bonus = 1500. Sales = 40000, bonus = 500. Sales = 30000, bonus = 100.

A single IF THEN ELSIF statement is easier to understand than a logically equivalent nested IF THEN ELSE statement:

-- IF THEN ELSIF statement IF condition_1 THEN statements_1; ELSIF condition_2 THEN statements_2; ELSIF condition_3 THEN statement_3; END IF; -- Logically equivalent nested IF THEN ELSE statements IF condition_1 THEN statements_1; ELSE IF condition_2 THEN statements_2; ELSE IF condition_3 THEN statements_3; END IF; END IF; END IF;

Example 4-5 uses an IF THEN ELSIF statement with many ELSIF clauses to compare a single value to many possible values. For this purpose, a simple CASE statement is clearer—see Example 4-6.

Example 4-5 IF THEN ELSIF Statement Simulates Simple CASE Statement

DECLARE grade CHAR(1); BEGIN grade := 'B'; IF grade = 'A' THEN DBMS_OUTPUT.PUT_LINE('Excellent'); ELSIF grade = 'B' THEN DBMS_OUTPUT.PUT_LINE('Very Good'); ELSIF grade = 'C' THEN DBMS_OUTPUT.PUT_LINE('Good'); ELSIF grade = 'D' THEN DBMS_OUTPUT. PUT_LINE('Fair'); ELSIF grade = 'F' THEN DBMS_OUTPUT.PUT_LINE('Poor'); ELSE DBMS_OUTPUT.PUT_LINE('No such grade'); END IF; END; /

Result:

Very Good

Simple CASE Statement

The simple CASE statement has this structure:

CASE selector WHEN selector_value_1 THEN statements_1 WHEN selector_value_2 THEN statements_2 ... WHEN selector_value_n THEN statements_n [ ELSE else_statements ] END CASE;]

The selector is an expression (typically a single variable). Each selector_value can be either a literal or an expression. (For complete syntax, see "CASE Statement".)

The simple CASE statement runs the first statements for which selector_value equals selector. Remaining conditions are not evaluated. If no selector_value equals selector, the CASE statement runs else_statements if they exist and raises the predefined exception CASE_NOT_FOUND otherwise.

Example 4-6 uses a simple CASE statement to compare a single value to many possible values. The CASE statement in Example 4-6 is logically equivalent to the IF THEN ELSIF statement in Example 4-5.

Example 4-6 Simple CASE Statement

DECLARE grade CHAR(1); BEGIN grade := 'B'; CASE grade WHEN 'A' THEN DBMS_OUTPUT.PUT_LINE('Excellent'); WHEN 'B' THEN DBMS_OUTPUT.PUT_LINE('Very Good'); WHEN 'C' THEN DBMS_OUTPUT.PUT_LINE('Good'); WHEN 'D' THEN DBMS_OUTPUT.PUT_LINE('Fair'); WHEN 'F' THEN DBMS_OUTPUT.PUT_LINE('Poor'); ELSE DBMS_OUTPUT.PUT_LINE('No such grade'); END CASE; END; /

Result:

Very Good

Note:

As in a simple CASE expression, if the selector in a simple CASE statement has the value NULL, it cannot be matched by WHEN NULL (see Example 2-51, "Simple CASE Expression with WHEN NULL"). Instead, use a searched CASE statement with WHEN condition IS NULL (see Example 2-53, "Searched CASE Expression with WHEN ... IS NULL").

Searched CASE Statement

The searched CASE statement has this structure:

CASE WHEN condition_1 THEN statements_1 WHEN condition_2 THEN statements_2 ... WHEN condition_n THEN statements_n [ ELSE else_statements ] END CASE;]

The searched CASE statement runs the first statements for which condition is true. Remaining conditions are not evaluated. If no condition is true, the CASE statement runs else_statements if they exist and raises the predefined exception CASE_NOT_FOUND otherwise. (For complete syntax, see "CASE Statement".)

The searched CASE statement in Example 4-7 is logically equivalent to the simple CASE statement in Example 4-6.

Example 4-7 Searched CASE Statement

DECLARE grade CHAR(1); BEGIN grade := 'B'; CASE WHEN grade = 'A' THEN DBMS_OUTPUT.PUT_LINE('Excellent'); WHEN grade = 'B' THEN DBMS_OUTPUT.PUT_LINE('Very Good'); WHEN grade = 'C' THEN DBMS_OUTPUT.PUT_LINE('Good'); WHEN grade = 'D' THEN DBMS_OUTPUT.PUT_LINE('Fair'); WHEN grade = 'F' THEN DBMS_OUTPUT.PUT_LINE('Poor'); ELSE DBMS_OUTPUT.PUT_LINE('No such grade'); END CASE; END; /

Result:

Very Good

In both Example 4-7 and Example 4-6, the ELSE clause can be replaced by an EXCEPTION part. Example 4-8 is logically equivalent to Example 4-7.

Example 4-8 EXCEPTION Instead of ELSE Clause in CASE Statement

DECLARE grade CHAR(1); BEGIN grade := 'B'; CASE WHEN grade = 'A' THEN DBMS_OUTPUT.PUT_LINE('Excellent'); WHEN grade = 'B' THEN DBMS_OUTPUT.PUT_LINE('Very Good'); WHEN grade = 'C' THEN DBMS_OUTPUT.PUT_LINE('Good'); WHEN grade = 'D' THEN DBMS_OUTPUT.PUT_LINE('Fair'); WHEN grade = 'F' THEN DBMS_OUTPUT.PUT_LINE('Poor'); END CASE; EXCEPTION WHEN CASE_NOT_FOUND THEN DBMS_OUTPUT.PUT_LINE('No such grade'); END; /

Result:

Very Good

LOOP Statements

Loop statements run the same statements with a series of different values. The loop statements are:

• Basic LOOP

• FOR LOOP

• Cursor FOR LOOP

• WHILE LOOP

The statements that exit a loop are:

• EXIT

• EXIT WHEN

The statements that exit the current iteration of a loop are:

• CONTINUE

• CONTINUE WHEN

EXIT, EXIT WHEN, CONTINUE, and CONTINUE WHEN and can appear anywhere inside a loop, but not outside a loop. Oracle recommends using these statements instead of the "GOTO Statement", which can exit a loop or the current iteration of a loop by transferring control to a statement outside the loop. (A raised exception also exits a loop. For information about exceptions, see "Overview of Exception Handling".)

LOOP statements can be labeled, and LOOP statements can be nested. Labels are recommended for nested loops to improve readability. You must ensure that the label in the END LOOP statement matches the label at the beginning of the same loop statement (the compiler does not check).

Topics

• Basic LOOP Statement

• EXIT Statement

• EXIT WHEN Statement

• CONTINUE Statement

• CONTINUE WHEN Statement

• FOR LOOP Statement

• WHILE LOOP Statement

For information about the cursor FOR LOOP, see "Query Result Set Processing With Cursor FOR LOOP Statements".

Basic LOOP Statement

The basic LOOP statement has this structure:

[ label ] LOOP statements END LOOP [ label ];

With each iteration of the loop, the statements run and control returns to the top of the loop. To prevent an infinite loop, a statement or raised exception must exit the loop.

See Also:

"Basic LOOP Statement"

EXIT Statement

The EXIT statement exits the current iteration of a loop unconditionally and transfers control to the end of either the current loop or an enclosing labeled loop.

In Example 4-9, the EXIT statement inside the basic LOOP statement transfers control unconditionally to the end of the current loop.

Example 4-9 Basic LOOP Statement with EXIT Statement

DECLARE x NUMBER := 0; BEGIN LOOP DBMS_OUTPUT.PUT_LINE ('Inside loop: x = ' || TO_CHAR(x)); x := x + 1; IF x > 3 THEN EXIT; END IF; END LOOP; -- After EXIT, control resumes here DBMS_OUTPUT.PUT_LINE(' After loop: x = ' || TO_CHAR(x)); END; /

Result:

Inside loop: x = 0 Inside loop: x = 1 Inside loop: x = 2 Inside loop: x = 3 After loop: x = 4

See Also:

"EXIT Statement"

EXIT WHEN Statement

The EXIT WHEN statement exits the current iteration of a loop when the condition in its WHEN clause is true, and transfers control to the end of either the current loop or an enclosing labeled loop.

Each time control reaches the EXIT WHEN statement, the condition in its WHEN clause is evaluated. If the condition is not true, the EXIT WHEN statement does nothing. To prevent an infinite loop, a statement inside the loop must make the condition true, as in Example 4-10.

In Example 4-10, the EXIT WHEN statement inside the basic LOOP statement transfers control to the end of the current loop when x is greater than 3. Example 4-10 is logically equivalent to Example 4-9.

Example 4-10 Basic LOOP Statement with EXIT WHEN Statement

DECLARE x NUMBER := 0; BEGIN LOOP DBMS_OUTPUT.PUT_LINE('Inside loop: x = ' || TO_CHAR(x)); x := x + 1; -- prevents infinite loop EXIT WHEN x > 3; END LOOP; -- After EXIT statement, control resumes here DBMS_OUTPUT.PUT_LINE('After loop: x = ' || TO_CHAR(x)); END; /

Result:

Inside loop: x = 0 Inside loop: x = 1 Inside loop: x = 2 Inside loop: x = 3 After loop: x = 4

See Also:

"EXIT Statement"

In Example 4-11, one basic LOOP statement is nested inside the other, and both have labels. The inner loop has two EXIT WHEN statements; one that exits the inner loop and one that exits the outer loop.

Example 4-11 Nested, Labeled Basic LOOP Statements with EXIT WHEN Statements

DECLARE s PLS_INTEGER := 0; i PLS_INTEGER := 0; j PLS_INTEGER; BEGIN <<outer_loop>> LOOP i := i + 1; j := 0; <<inner_loop>> LOOP j := j + 1; s := s + i * j; -- Sum several products EXIT inner_loop WHEN (j > 5); EXIT outer_loop WHEN ((i * j) > 15); END LOOP inner_loop; END LOOP outer_loop; DBMS_OUTPUT.PUT_LINE ('The sum of products equals: ' || TO_CHAR(s)); END; /

Result:

The sum of products equals: 166

An EXIT WHEN statement in an inner loop can transfer control to an outer loop only if the outer loop is labeled.

In Example 4-12, the outer loop is not labeled; therefore, the inner loop cannot transfer control to it.

Example 4-12 Nested, Unabeled Basic LOOP Statements with EXIT WHEN Statements

DECLARE i PLS_INTEGER := 0; j PLS_INTEGER := 0; BEGIN LOOP i := i + 1; DBMS_OUTPUT.PUT_LINE ('i = ' || i); LOOP j := j + 1; DBMS_OUTPUT.PUT_LINE ('j = ' || j); EXIT WHEN (j > 3); END LOOP; DBMS_OUTPUT.PUT_LINE ('Exited inner loop'); EXIT WHEN (i > 2); END LOOP; DBMS_OUTPUT.PUT_LINE ('Exited outer loop'); END; /

Result:

i = 1 j = 1 j = 2 j = 3 j = 4 Exited inner loop i = 2 j = 5 Exited inner loop i = 3 j = 6 Exited inner loop Exited outer loop PL/SQL procedure successfully completed.

CONTINUE Statement

The CONTINUE statement exits the current iteration of a loop unconditionally and transfers control to the next iteration of either the current loop or an enclosing labeled loop.

In Example 4-13, the CONTINUE statement inside the basic LOOP statement transfers control unconditionally to the next iteration of the current loop.

Example 4-13 CONTINUE Statement in Basic LOOP Statement

DECLARE x NUMBER := 0; BEGIN LOOP -- After CONTINUE statement, control resumes here DBMS_OUTPUT.PUT_LINE ('Inside loop: x = ' || TO_CHAR(x)); x := x + 1; IF x < 3 THEN CONTINUE; END IF; DBMS_OUTPUT.PUT_LINE ('Inside loop, after CONTINUE: x = ' || TO_CHAR(x)); EXIT WHEN x = 5; END LOOP; DBMS_OUTPUT.PUT_LINE (' After loop: x = ' || TO_CHAR(x)); END; /

Result:

Inside loop: x = 0 Inside loop: x = 1 Inside loop: x = 2 Inside loop, after CONTINUE: x = 3 Inside loop: x = 3 Inside loop, after CONTINUE: x = 4 Inside loop: x = 4 Inside loop, after CONTINUE: x = 5 After loop: x = 5

See Also:

"CONTINUE Statement"

CONTINUE WHEN Statement

The CONTINUE WHEN statement exits the current iteration of a loop when the condition in its WHEN clause is true, and transfers control to the next iteration of either the current loop or an enclosing labeled loop.

Each time control reaches the CONTINUE WHEN statement, the condition in its WHEN clause is evaluated. If the condition is not true, the CONTINUE WHEN statement does nothing.

In Example 4-14, the CONTINUE WHEN statement inside the basic LOOP statement transfers control to the next iteration of the current loop when x is less than 3. Example 4-14 is logically equivalent to Example 4-13.

Example 4-14 CONTINUE WHEN Statement in Basic LOOP Statement

DECLARE x NUMBER := 0; BEGIN LOOP -- After CONTINUE statement, control resumes here DBMS_OUTPUT.PUT_LINE ('Inside loop: x = ' || TO_CHAR(x)); x := x + 1; CONTINUE WHEN x < 3; DBMS_OUTPUT.PUT_LINE ('Inside loop, after CONTINUE: x = ' || TO_CHAR(x)); EXIT WHEN x = 5; END LOOP; DBMS_OUTPUT.PUT_LINE (' After loop: x = ' || TO_CHAR(x)); END; /

Result:

Inside loop: x = 0 Inside loop: x = 1 Inside loop: x = 2 Inside loop, after CONTINUE: x = 3 Inside loop: x = 3 Inside loop, after CONTINUE: x = 4 Inside loop: x = 4 Inside loop, after CONTINUE: x = 5 After loop: x = 5

See Also:

"CONTINUE Statement"

FOR LOOP Statement

The FOR LOOP statement runs one or more statements while the loop index is in a specified range. The statement has this structure:

[ label ] FOR index IN [ REVERSE ] lower_bound..upper_bound LOOP statements END LOOP [ label ];

Without REVERSE, the value of index starts at lower_bound and increases by one with each iteration of the loop until it reaches upper_bound. If lower_bound is greater than upper_bound, then the statements never run.

With REVERSE, the value of index starts at upper_bound and decreases by one with each iteration of the loop until it reaches lower_bound. If upper_bound is less than lower_bound, then the statements never run.

An EXIT, EXIT WHEN, CONTINUE, or CONTINUE WHEN in the statements can cause the loop or the current iteration of the loop to end early.

Tip:

To process the rows of a query result set, use a cursor FOR LOOP, which has a query instead of a range of integers. For details, see "Query Result Set Processing With Cursor FOR LOOP Statements".

See Also:

"FOR LOOP Statement"

In Example 4-15, index is i, lower_bound is 1, and upper_bound is 3. The loop prints the numbers from 1 to 3.

Example 4-15 FOR LOOP Statements

BEGIN DBMS_OUTPUT.PUT_LINE ('lower_bound < upper_bound'); FOR i IN 1..3 LOOP DBMS_OUTPUT.PUT_LINE (i); END LOOP; DBMS_OUTPUT.PUT_LINE ('lower_bound = upper_bound'); FOR i IN 2..2 LOOP DBMS_OUTPUT.PUT_LINE (i); END LOOP; DBMS_OUTPUT.PUT_LINE ('lower_bound > upper_bound'); FOR i IN 3..1 LOOP DBMS_OUTPUT.PUT_LINE (i); END LOOP; END; /

Result:

lower_bound < upper_bound 1 2 3 lower_bound = upper_bound 2 lower_bound > upper_bound

The FOR LOOP statement in Example 4-16 is the reverse of the one in Example 4-15: It prints the numbers from 3 to 1.

Example 4-16 Reverse FOR LOOP Statements

BEGIN DBMS_OUTPUT.PUT_LINE ('upper_bound > lower_bound'); FOR i IN REVERSE 1..3 LOOP DBMS_OUTPUT.PUT_LINE (i); END LOOP; DBMS_OUTPUT.PUT_LINE ('upper_bound = lower_bound'); FOR i IN REVERSE 2..2 LOOP DBMS_OUTPUT.PUT_LINE (i); END LOOP; DBMS_OUTPUT.PUT_LINE ('upper_bound < lower_bound'); FOR i IN REVERSE 3..1 LOOP DBMS_OUTPUT.PUT_LINE (i); END LOOP; END; /

Result:

upper_bound > lower_bound 3 2 1 upper_bound = lower_bound 2 upper_bound < lower_bound

In some languages, the FOR LOOP has a STEP clause that lets you specify a loop index increment other than 1. To simulate the STEP clause in PL/SQL, multiply each reference to the loop index by the desired increment.

In Example 4-17, the FOR LOOP effectively increments the index by five.

Example 4-17 Simulating STEP Clause in FOR LOOP Statement

DECLARE step PLS_INTEGER := 5; BEGIN FOR i IN 1..3 LOOP DBMS_OUTPUT.PUT_LINE (i*step); END LOOP; END; /

Result:

5 10 15

Topics

• FOR LOOP Index

• Lower Bound and Upper Bound

• EXIT WHEN or CONTINUE WHEN Statement in FOR LOOP Statement

FOR LOOP Index

The index of a FOR LOOP statement is implicitly declared as a variable of type PLS_INTEGER that is local to the loop. The statements in the loop can read the value of the index, but cannot change it. Statements outside the loop cannot reference the index. After the FOR LOOP statement runs, the index is undefined. (A loop index is sometimes called a loop counter.)

In Example 4-18, the FOR LOOP statement tries to change the value of its index, causing an error.

Example 4-18 FOR LOOP Statement Tries to Change Index Value

BEGIN FOR i IN 1..3 LOOP IF i < 3 THEN DBMS_OUTPUT.PUT_LINE (TO_CHAR(i)); ELSE i := 2; END IF; END LOOP; END; /

Result:

i := 2; * ERROR at line 6: ORA-06550: line 6, column 8: PLS-00363: expression 'I' cannot be used as an assignment target ORA-06550: line 6, column 8: PL/SQL: Statement ignored

In Example 4-19, a statement outside the FOR LOOP statement references the loop index, causing an error.

Example 4-19 Outside Statement References FOR LOOP Statement Index

BEGIN FOR i IN 1..3 LOOP DBMS_OUTPUT.PUT_LINE ('Inside loop, i is ' || TO_CHAR(i)); END LOOP; DBMS_OUTPUT.PUT_LINE ('Outside loop, i is ' || TO_CHAR(i)); END; /

Result:

DBMS_OUTPUT.PUT_LINE ('Outside loop, i is ' || TO_CHAR(i)); * ERROR at line 6: ORA-06550: line 6, column 58: PLS-00201: identifier 'I' must be declared ORA-06550: line 6, column 3: PL/SQL: Statement ignored

If the index of a FOR LOOP statement has the same name as a variable declared in an enclosing block, the local implicit declaration hides the other declaration, as Example 4-20 shows.

Example 4-20 FOR LOOP Statement Index with Same Name as Variable

DECLARE i NUMBER := 5; BEGIN FOR i IN 1..3 LOOP DBMS_OUTPUT.PUT_LINE ('Inside loop, i is ' || TO_CHAR(i)); END LOOP; DBMS_OUTPUT.PUT_LINE ('Outside loop, i is ' || TO_CHAR(i)); END; /

Result:

Inside loop, i is 1 Inside loop, i is 2 Inside loop, i is 3 Outside loop, i is 5

Example 4-21 shows how to change Example 4-20 to allow the statement inside the loop to reference the variable declared in the enclosing block.

Example 4-21 FOR LOOP Statement References Variable with Same Name as Index

<<main>> -- Label block. DECLARE i NUMBER := 5; BEGIN FOR i IN 1..3 LOOP DBMS_OUTPUT.PUT_LINE ( 'local: ' || TO_CHAR(i) || ', global: ' || TO_CHAR(main.i) -- Qualify reference with block label. ); END LOOP; END main; /

Result:

local: 1, global: 5 local: 2, global: 5 local: 3, global: 5

In Example 4-22, the indexes of the nested FOR LOOP statements have the same name. The inner loop references the index of the outer loop by qualifying the reference with the label of the outer loop. For clarity only, the inner loop also qualifies the reference to its own index with its own label.

Example 4-22 Nested FOR LOOP Statements with Same Index Name

BEGIN <<outer_loop>> FOR i IN 1..3 LOOP <<inner_loop>> FOR i IN 1..3 LOOP IF outer_loop.i = 2 THEN DBMS_OUTPUT.PUT_LINE ('outer: ' || TO_CHAR(outer_loop.i) || ' inner: ' || TO_CHAR(inner_loop.i)); END IF; END LOOP inner_loop; END LOOP outer_loop; END; /

Result:

outer: 2 inner: 1 outer: 2 inner: 2 outer: 2 inner: 3

Lower Bound and Upper Bound

The lower and upper bounds of a FOR LOOP statement can be either numeric literals, numeric variables, or numeric expressions. If a bound does not have a numeric value, then PL/SQL raises the predefined exception VALUE_ERROR.

Example 4-23 FOR LOOP Statement Bounds

DECLARE first INTEGER := 1; last INTEGER := 10; high INTEGER := 100; low INTEGER := 12; BEGIN -- Bounds are numeric literals: FOR j IN -5..5 LOOP NULL; END LOOP; -- Bounds are numeric variables: FOR k IN REVERSE first..last LOOP NULL; END LOOP; -- Lower bound is numeric literal, -- Upper bound is numeric expression: FOR step IN 0..(TRUNC(high/low) * 2) LOOP NULL; END LOOP; END; /

In Example 4-24, the upper bound of the FOR LOOP statement is a variable whose value is determined at run time.

Example 4-24 Specifying FOR LOOP Statement Bounds at Run Time

DROP TABLE temp; CREATE TABLE temp ( emp_no NUMBER, email_addr VARCHAR2(50) ); DECLARE emp_count NUMBER; BEGIN SELECT COUNT(employee_id) INTO emp_count FROM employees; FOR i IN 1..emp_count LOOP INSERT INTO temp (emp_no, email_addr) VALUES(i, 'to be added later'); END LOOP; END; /

EXIT WHEN or CONTINUE WHEN Statement in FOR LOOP Statement

Suppose that you must exit a FOR LOOP statement immediately if a certain condition arises. You can put the condition in an EXIT WHEN statement inside the FOR LOOP statement.

In Example 4-25, the FOR LOOP statement executes 10 times unless the FETCH statement inside it fails to return a row, in which case it ends immediately.

Example 4-25 EXIT WHEN Statement in FOR LOOP Statement

DECLARE v_employees employees%ROWTYPE; CURSOR c1 is SELECT * FROM employees; BEGIN OPEN c1; -- Fetch entire row into v_employees record: FOR i IN 1..10 LOOP FETCH c1 INTO v_employees; EXIT WHEN c1%NOTFOUND; -- Process data here END LOOP; CLOSE c1; END; /

Now suppose that the FOR LOOP statement that you must exit early is nested inside another FOR LOOP statement. If, when you exit the inner loop early, you also want to exit the outer loop, then label the outer loop and specify its name in the EXIT WHEN statement, as in Example 4-26.

If you want to exit the inner loop early but complete the current iteration of the outer loop, then label the outer loop and specify its name in the CONTINUE WHEN statement, as in Example 4-27.

Example 4-26 EXIT WHEN Statement in Inner FOR LOOP Statement

DECLARE v_employees employees%ROWTYPE; CURSOR c1 is SELECT * FROM employees; BEGIN OPEN c1; -- Fetch entire row into v_employees record: <<outer_loop>> FOR i IN 1..10 LOOP -- Process data here FOR j IN 1..10 LOOP FETCH c1 INTO v_employees; EXIT outer_loop WHEN c1%NOTFOUND; -- Process data here END LOOP; END LOOP outer_loop; CLOSE c1; END; /

Example 4-27 CONTINUE WHEN Statement in Inner FOR LOOP Statement

DECLARE v_employees employees%ROWTYPE; CURSOR c1 is SELECT * FROM employees; BEGIN OPEN c1; -- Fetch entire row into v_employees record: <<outer_loop>> FOR i IN 1..10 LOOP -- Process data here FOR j IN 1..10 LOOP FETCH c1 INTO v_employees; CONTINUE outer_loop WHEN c1%NOTFOUND; -- Process data here END LOOP; END LOOP outer_loop; CLOSE c1; END; /

See Also:

"Overview of Exception Handling" for information about exceptions, which can also cause a loop to end immediately if a certain condition arises

WHILE LOOP Statement

The WHILE LOOP statement runs one or more statements while a condition is true. It has this structure:

[ label ] WHILE condition LOOP statements END LOOP [ label ];

If the condition is true, the statements run and control returns to the top of the loop, where condition is evaluated again. If the condition is not true, control transfers to the statement after the WHILE LOOP statement. To prevent an infinite loop, a statement inside the loop must make the condition false or null. For complete syntax, see "WHILE LOOP Statement".

An EXIT, EXIT WHEN, CONTINUE, or CONTINUE WHEN in the statements can cause the loop or the current iteration of the loop to end early.

In Example 4-28, the statements in the first WHILE LOOP statement never run, and the statements in the second WHILE LOOP statement run once.

Example 4-28 WHILE LOOP Statements

DECLARE done BOOLEAN := FALSE; BEGIN WHILE done LOOP DBMS_OUTPUT.PUT_LINE ('This line does not print.'); done := TRUE; -- This assignment is not made. END LOOP; WHILE NOT done LOOP DBMS_OUTPUT.PUT_LINE ('Hello, world!'); done := TRUE; END LOOP; END; /

Result:

Hello, world!

Some languages have a LOOP UNTIL or REPEAT UNTIL structure, which tests a condition at the bottom of the loop instead of at the top, so that the statements run at least once. To simulate this structure in PL/SQL, use a basic LOOP statement with an EXIT WHEN statement:

LOOP statements EXIT WHEN condition; END LOOP;

Sequential Control Statements

Unlike the IF and LOOP statements, the sequential control statements GOTO and NULL are not crucial to PL/SQL programming.

The GOTO statement, which goes to a specified statement, is seldom needed. Occasionally, it simplifies logic enough to warrant its use.

The NULL statement, which does nothing, can improve readability by making the meaning and action of conditional statements clear.

Topics

• GOTO Statement

• NULL Statement

GOTO Statement

The GOTO statement transfers control to a label unconditionally. The label must be unique in its scope and must precede an executable statement or a PL/SQL block. When run, the GOTO statement transfers control to the labeled statement or block. For GOTO statement restrictions, see "GOTO Statement".

Use GOTO statements sparingly—overusing them results in code that is hard to understand and maintain. Do not use a GOTO statement to transfer control from a deeply nested structure to an exception handler. Instead, raise an exception. For information about the PL/SQL exception-handling mechanism, see Chapter 11, "PL/SQL Error Handling."

Example 4-29 GOTO Statement

DECLARE p VARCHAR2(30); n PLS_INTEGER := 37; BEGIN FOR j in 2..ROUND(SQRT(n)) LOOP IF n MOD j = 0 THEN p := ' is not a prime number'; GOTO print_now; END IF; END LOOP; p := ' is a prime number'; <<print_now>> DBMS_OUTPUT.PUT_LINE(TO_CHAR(n) || p); END; /

Result:

37 is a prime number

A label can appear only before a block (as in Example 4-21) or before a statement (as in Example 4-29), not in a statement, as in Example 4-30.

Example 4-30 Incorrect Label Placement

DECLARE done BOOLEAN; BEGIN FOR i IN 1..50 LOOP IF done THEN GOTO end_loop; END IF; <<end_loop>> END LOOP; END; /

Result:

END LOOP; * ERROR at line 9: ORA-06550: line 9, column 3: PLS-00103: Encountered the symbol "END" when expecting one of the following: ( begin case declare exit for goto if loop mod null raise return select update while with <an identifier> <a double-quoted delimited-identifier> <a bind variable> << continue close current delete fetch lock insert open rollback savepoint set sql run commit forall merge pipe purge

To correct Example 4-30, add a NULL statement, as in Example 4-31.

Example 4-31 GOTO Statement Goes to Labeled NULL Statement

DECLARE done BOOLEAN; BEGIN FOR i IN 1..50 LOOP IF done THEN GOTO end_loop; END IF; <<end_loop>> NULL; END LOOP; END; /

A GOTO statement can transfer control to an enclosing block from the current block, as in Example 4-32.

Example 4-32 GOTO Statement Transfers Control to Enclosing Block

DECLARE v_last_name VARCHAR2(25); v_emp_id NUMBER(6) := 120; BEGIN <<get_name>> SELECT last_name INTO v_last_name FROM employees WHERE employee_id = v_emp_id; BEGIN DBMS_OUTPUT.PUT_LINE (v_last_name); v_emp_id := v_emp_id + 5; IF v_emp_id < 120 THEN GOTO get_name; END IF; END; END; /

Result:

Weiss

The GOTO statement transfers control to the first enclosing block in which the referenced label appears.

The GOTO statement in Example 4-33 transfers control into an IF statement, causing an error.

Example 4-33 GOTO Statement Cannot Transfer Control into IF Statement

DECLARE valid BOOLEAN := TRUE; BEGIN GOTO update_row; IF valid THEN <<update_row>> NULL; END IF; END; /

Result:

GOTO update_row; * ERROR at line 4: ORA-06550: line 4, column 3: PLS-00375: illegal GOTO statement; this GOTO cannot transfer control to label 'UPDATE_ROW' ORA-06550: line 6, column 12: PL/SQL: Statement ignored

NULL Statement

The NULL statement only passes control to the next statement. Some languages refer to such an instruction as a no-op (no operation).

Some uses for the NULL statement are:

• To provide a target for a GOTO statement, as in Example 4-31.

• To improve readability by making the meaning and action of conditional statements clear, as in Example 4-34

• To create placeholders and stub subprograms, as in Example 4-35

• To show that you are aware of a possibility, but that no action is necessary, as in Example 4-36

In Example 4-34, the NULL statement emphasizes that only salespersons receive commissions.

Example 4-34 NULL Statement Showing No Action

DECLARE v_job_id VARCHAR2(10); v_emp_id NUMBER(6) := 110; BEGIN SELECT job_id INTO v_job_id FROM employees WHERE employee_id = v_emp_id; IF v_job_id = 'SA_REP' THEN UPDATE employees SET commission_pct = commission_pct * 1.2; ELSE NULL; -- Employee is not a sales rep END IF; END; /

In Example 4-35, the NULL statement lets you compile this subprogram and fill in the real body later.

Note:

Using the NULL statement might raise an unreachable code warning if warnings are enabled. For information about warnings, see "Compile-Time Warnings".

Example 4-35 NULL Statement as Placeholder During Subprogram Creation

CREATE OR REPLACE PROCEDURE award_bonus ( emp_id NUMBER, bonus NUMBER ) AS BEGIN -- Executable part starts here NULL; -- Placeholder -- (raises "unreachable code" if warnings enabled) END award_bonus; /

In Example 4-36, the NULL statement shows that you have chosen to take no action for grades other than A, B, C, D, and F.

Example 4-36 NULL Statement in ELSE Clause of Simple CASE Statement

CREATE OR REPLACE PROCEDURE print_grade ( grade CHAR ) AUTHID DEFINER AS BEGIN CASE grade WHEN 'A' THEN DBMS_OUTPUT.PUT_LINE('Excellent'); WHEN 'B' THEN DBMS_OUTPUT.PUT_LINE('Very Good'); WHEN 'C' THEN DBMS_OUTPUT.PUT_LINE('Good'); WHEN 'D' THEN DBMS_OUTPUT.PUT_LINE('Fair'); WHEN 'F' THEN DBMS_OUTPUT.PUT_LINE('Poor'); ELSE NULL; END CASE; END; /