ASA SQL Reference
  SQL Statements

CASE statement

Description 

Use this statement to select an execution path based on multiple cases.

Syntax 1 

CASE value-expression
WHEN [ constant | NULL ] THEN statement-list ...
[ WHEN [ constant | NULL ] THEN statement-list ] ...
[ ELSE statement-list ]
END CASE

Syntax 2 

CASE
WHEN [ search-condition | NULL] THEN statement-list ...
[ WHEN [ search-condition | NULL] THEN statement-list ] ...
[ ELSE statement-list ]
END CASE

Usage 

Syntax 1    The CASE statement is a control statement that allows you to choose a list of SQL statements to execute based on the value of an expression. The value-expression is an expression that takes on a single value, which may be a string, a number, a date, or other SQL data type. If a WHEN clause exists for the value of value-expression, the statement-list in the WHEN clause is executed. If no appropriate WHEN clause exists, and an ELSE clause exists, the statement-list in the ELSE clause is executed. Execution resumes at the first statement after the END CASE.

If the value-expression can be null, use the ISNULL function to replace the NULL value-expression with a different expression.

For more information about the ISNULL function, see ISNULL function [Data type conversion].

Syntax 2    With this form, the statements are executed for the first satisfied search-condition in the CASE statement. The ELSE clause is executed if none of the search-conditions are met.

If the expression can be NULL, use the following syntax for the first search-condition:

WHEN search-condition IS NULL THEN statement-list

For more information about NULL values, see Unknown Values: NULL.

Permissions 

None.

Side effects 

None.

See also 

BEGIN statement

Using Procedures, Triggers, and Batches

Standards and compatibility 

• SQL/92    Persistent Stored Module feature. Adaptive Server Anywhere supports the CASE statement allowing WHEN NULL. This is a vendor extension to the SQL/92 standard.

• SQL/99    Persistent Stored Module feature. Adaptive Server Anywhere supports the CASE statement allowing WHEN NULL. This is a vendor extension to the SQL/92 standard.

• Sybase    Not supported by Adaptive Server Enterprise.

Example 

The following procedure using a case statement classifies the products listed in the product table of the sample database into one of shirt, hat, shorts, or unknown.

CREATE PROCEDURE ProductType (IN product_id INT, OUT type CHAR(10))
BEGIN
   DECLARE prod_name CHAR(20);
   SELECT name INTO prod_name FROM "DBA"."product"
   WHERE id = product_id;
   CASE prod_name
   WHEN 'Tee Shirt' THEN
      SET type = 'Shirt'
   WHEN 'Sweatshirt' THEN
      SET type = 'Shirt'
   WHEN 'Baseball Cap' THEN
      SET type = 'Hat'
   WHEN 'Visor' THEN
      SET type = 'Hat'
   WHEN 'Shorts' THEN
      SET type = 'Shorts'
   ELSE
      SET type = 'UNKNOWN'
   END CASE;
END

The following example uses Syntax 2 to generate a message about product quantity within the sample database.

CREATE PROCEDURE StockLevel (IN product_id INT)
BEGIN
   DECLARE qty INT;
   SELECT quantity INTO qty FROM product
   WHERE id = product_id;
   CASE
   WHEN qty < 30 THEN
      MESSAGE 'Order Stock' TO CLIENT;
   WHEN qty > 100 THEN
      MESSAGE 'Overstocked' TO CLIENT;
   ELSE
      MESSAGE 'Sufficient stock on hand' TO CLIENT;
   END CASE;
END