LOOP Statements
A LOOP statement executes a sequence of statements multiple times. PL/SQL provides these loop statements:
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Basic loop
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WHILEloop -
FORloop -
Cursor
FORloop
Description of the illustration basic_loop_statement.gif
Description of the illustration while_loop_statement.gif
Description of the illustration for_loop_statement.gif
Description of the illustration cursor_for_loop_statement.gif
Keyword and Parameter Descriptions
A loop that executes an unlimited number of times. It encloses a sequence of statements between the keywords LOOP and END LOOP. With each iteration, the sequence of statements is executed, then control resumes at the top of the loop. An EXIT, GOTO, or RAISE statement branches out of the loop. A raised exception also ends the loop.
If and only if the value of this expression is TRUE, the statements after LOOP execute.
Issues a SQL query and loops through the rows in the result set. This is a convenient technique that makes processing a query as simple as reading lines of text in other programming languages.
A cursor FOR loop implicitly declares its loop index as a %ROWTYPE record, opens a cursor, repeatedly fetches rows of values from the result set into fields in the record, and closes the cursor when all rows were processed.
An explicit cursor previously declared within the current scope. When the cursor FOR loop is entered, cursor_name cannot refer to a cursor already opened by an OPEN statement or an enclosing cursor FOR loop.
A variable declared as the formal parameter of a cursor. For the syntax of cursor_parameter_declaration, see Explicit Cursor. A cursor parameter can appear in a query wherever a constant can appear. The formal parameters of a cursor must be IN parameters.
Numeric FOR_LOOP loops iterate over a specified range of integers. The range is part of an iteration scheme, which is enclosed by the keywords FOR and LOOP.
The range is evaluated when the FOR loop is first entered and is never re-evaluated. The loop body is executed once for each integer in the range defined by lower_bound..upper_bound. After each iteration, the loop index is incremented.
An undeclared identifier that names the loop index (sometimes called a loop counter). Its scope is the loop itself; you cannot reference the index outside the loop.
The implicit declaration of index_name overrides any other declaration outside the loop. To refer to another variable with the same name, use a label. See Example 4-22, "Referencing Global Variable with Same Name as Loop Counter".
Inside a loop, the index is treated like a constant: it can appear in expressions, but cannot be assigned a value.
An optional undeclared identifier that labels a loop. label_name must be enclosed by double angle brackets and must appear at the beginning of the loop. Optionally, label_name (not enclosed in angle brackets) can also appear at the end of the loop.
You can use label_name in an EXIT statement to exit the loop labeled by label_name. You can exit not only the current loop, but any enclosing loop.
You cannot reference the index of a FOR loop from a nested FOR loop if both indexes have the same name, unless the outer loop is labeled by label_name and you use dot notation. See Example 4-23, "Referencing Outer Counter with Same Name as Inner Counter".
Expressions that return numbers. Otherwise, PL/SQL raises the predefined exception VALUE_ERROR. The expressions are evaluated only when the loop is first entered. The lower bound need not be 1, it can be a negative integer as in the following example:
FOR i IN -5..10
The loop counter increment (or decrement) must be 1.
Internally, PL/SQL assigns the values of the bounds to temporary PLS_INTEGER variables, and, if necessary, rounds the values to the nearest integer. The magnitude range of a PLS_INTEGER is -2147483648 to 2147483647, represented in 32 bits. If a bound evaluates to a number outside that range, you get a numeric overflow error when PL/SQL attempts the assignment. See PLS_INTEGER and BINARY_INTEGER Data Types.
By default, the loop index is assigned the value of lower_bound. If that value is not greater than the value of upper_bound, the sequence of statements in the loop is executed, then the index is incremented. If the value of the index is still not greater than the value of upper_bound, the sequence of statements is executed again. This process repeats until the value of the index is greater than the value of upper_bound. At that point, the loop completes.
An implicitly declared record. The record has the same structure as a row retrieved by cursor_name or select_statement.
The record is defined only inside the loop. You cannot refer to its fields outside the loop. The implicit declaration of record_name overrides any other declaration outside the loop. You cannot refer to another record with the same name inside the loop unless you qualify the reference using a block label.
Fields in the record store column values from the implicitly fetched row. The fields have the same names and data types as their corresponding columns. To access field values, you use dot notation, as follows:
record_name.field_name
Select-items fetched from the FOR loop cursor must have simple names or, if they are expressions, must have aliases. In the following example, wages is an alias for the select item salary+NVL(commission_pct,0)*1000:
CURSOR c1 IS SELECT employee_id, salary + NVL(commission_pct,0) * 1000 wages FROM employees ...
By default, iteration proceeds upward from the lower bound to the upper bound. If you use the keyword REVERSE, iteration proceeds downward from the upper bound to the lower bound. An example follows:
BEGIN FOR i IN REVERSE 1..10 LOOP -- i starts at 10, ends at 1 DBMS_OUTPUT.PUT_LINE(i); -- statements here execute 10 times END LOOP; END; /
The loop index is assigned the value of upper_bound. If that value is not less than the value of lower_bound, the sequence of statements in the loop is executed, then the index is decremented. If the value of the index is still not less than the value of lower_bound, the sequence of statements is executed again. This process repeats until the value of the index is less than the value of lower_bound. At that point, the loop completes.
A query associated with an internal cursor unavailable to you. Its syntax is like that of select_into_statement without the INTO clause. See SELECT INTO Statement. PL/SQL automatically declares, opens, fetches from, and closes the internal cursor. Because select_statement is not an independent statement, the implicit cursor SQL does not apply to it.
The WHILE-LOOP statement associates a Boolean expression with a sequence of statements enclosed by the keywords LOOP and END LOOP. Before each iteration of the loop, the expression is evaluated. If the expression returns TRUE, the sequence of statements is executed, then control resumes at the top of the loop. If the expression returns FALSE or NULL, the loop is bypassed and control passes to the next statement.
You can use the EXIT WHEN statement to exit any loop prematurely. If the Boolean expression in the WHEN clause returns TRUE, the loop is exited immediately.
When you exit a cursor FOR loop, the cursor is closed automatically even if you use an EXIT or GOTO statement to exit the loop prematurely. The cursor is also closed automatically if an exception is raised inside the loop.