Advantage SQL Engine
The CASE expression evaluates a list of conditions and returns one of multiple possible result expressions. The CASE expressions let you use IF ... THEN ... ELSE logic in SQL statements.
CASE has two formats:
The simple CASE function compares an expression to a set of simple expressions to determine the result.
The searched CASE function evaluates a set of Boolean expressions to determine the result.
Both formats support an optional ELSE argument.
Syntax
The BNF syntax of CASE expression can be found in Advantage SQL Grammar.
Simple CASE function:
CASE input_expression
WHEN when_expression THEN result_expression
[ ...n ]
[
ELSE else_result_expression
]
END
Searched CASE function:
CASE
WHEN Boolean_expression THEN result_expression
[ ...n ]
[
ELSE else_result_expression
]
END
Arguments
input_expression
Is the expression evaluated when using the simple CASE format. input_expression is any valid Advantage SQL expression.
WHEN when_expression
Is a simple expression to which input_expression is compared when using the simple CASE format. when_expression is any valid Advantage SQL expression. The data types of input_expression and each when_expression must be the same or must be an implicit conversion.
n
Is a placeholder indicating that multiple WHEN when_expression THEN result_expression clauses, or multiple WHEN Boolean_expression THEN result_expression clauses can be used.
THEN result_expression
Is the expression returned when input_expression equals when_expression evaluates to TRUE, or Boolean_expression evaluates to TRUE. result expression is any valid Advantage SQL expression.
ELSE else_result_expression
Is the expression returned if no comparison operation evaluates to TRUE. If this argument is omitted and no comparison operation evaluates to TRUE, CASE returns NULL. else_result_expression is any valid Advantage SQL expression. The data types of else_result_expression and any result_expression must be the same or must be an implicit conversion.
WHEN Boolean_expression
Is the Boolean expression evaluated when using the searched CASE format. Boolean_expression is any valid Boolean expression.
Result Types
Returns the highest precedence type from the set of types in result_expressions and the optional else_result_expression.
Result Values
Evaluates input_expression, and then, in the order specified, evaluates input_expression = when_expression for each WHEN clause.
Returns the result_expression of the first (input_expression = when_expression) that evaluates to TRUE.
If no input_expression = when_expression evaluates to TRUE, Advantage returns the else_result_expression if an ELSE clause is specified, or a NULL value if no ELSE clause is specified.
Evaluates, in the order specified, Boolean_expression for each WHEN clause.
Returns result_expression of the first Boolean_expression that evaluates to TRUE.
If no Boolean_expression evaluates to TRUE, Advantage returns the else_result_expression if an ELSE clause is specified, or a NULL value if no ELSE clause is specified.
Examples
This example uses the CASE function to alter the display of the marriage status of the employees to make them more understandable.
SELECT Lastname + firstname As "Employee Name",
CASE married
WHEN True THEN 'Married'
WHEN False THEN 'Single'
ELSE 'Not yet known'
END As "Marital status"
FROM Employee
WHERE DateOfBirth >= '1970-03-31'
ORDER BY 2
Here is the result set:
Employee Name Marital Status
------------------- -------------------------
Smith John Married
Coles Becky Not yet known
Holmes Monique Single
Brown Terry Single
This example displays the current vacation earning schedule of the employees based on how long the employee has been working for the company.
SELECT Lastname + firstname As "Employee Name",
CASE
WHEN TimestampDiff( SQL_TSI_YEAR, CURR_DATE(), DateOfHire ) >= 10 THEN 7
WHEN TimestampDiff( SQL_TSI_YEAR, CURR_DATE(), DateOfHire ) >= 5 THEN 6.66
ELSE 5
END As "Vacation Hours Earned This period"
FROM Employee
ORDER BY 2 DESC
Here is the result set:
Employee Name Vacation Hours Earned this Period
--------------------- ---------------------------------
Schmidt Kathy 7.00
Wilkins Becky 6.66
Wong Wesley 5
Schmidt Mark 5
See Also