CASE
The CASE operator is used to evaluate several conditions and return a single value for the first matched condition. The CASE expression is similar to an IF-THEN-ELSE or a SWITCH statement used in many programming languages. However, in SQL, CASE is an expression, not a statement.
CASE has two formats:
Simple CASE
A simple CASE compares an expression to a set of simple expressions.
Syntax
CASE <comparison-value>
WHEN <conditional-expression 1> THEN <scalar-expression 1>
WHEN <conditional-expression 2> THEN <scalar-expression 2>
WHEN <conditional-expression 3> THEN <scalar-expression 3>
[ELSE <default-scalar-expression>]
END
Remarks
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Using CASE, you can express an alternate value to an underlying value. For example, if the underlying value is a code (such as 1, 2, 3), you can display it as a humanly readable string value (Small, Medium, Large), without affecting the underlying value. |
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If none of the test conditions is true, CASE returns the result contained in the optional ELSE case, if one is specified. |
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If no match is found and ELSE is not specified, ELSE NULL is assumed by default. |
Example
SELECT ProductID, Status, UnitPrice,
CASE Status
WHEN 'open' THEN UnitPrice * 1.10
WHEN 'closed' THEN UnitPrice * 1
ELSE UnitPrice
END
AS "New Price"
FROM /shared/examples/ds_orders/orderdetails
Searched CASE
A searched CASE compares an expression to a set of logical expressions.
Syntax
CASE
WHEN <conditional_expression_1> THEN <scalar_expression_1>
WHEN <conditional_expression_2> THEN <scalar_expression_2>
WHEN <conditional_expression_3> THEN <scalar_expression_3>
[ELSE <default_scalar_expression>]
END
Examples
SELECT ProductID, UnitPrice
CASE
WHEN UnitPrice <=100 THEN 'Between $1 and $100.00'
WHEN UnitPrice <=200 THEN 'Between $100.01 and $200.00'
ELSE 'Over $200.00'
END
AS "Price Range"
FROM /shared/examples/ds_orders/orderdetails
SELECT ProductID, UnitPrice
CASE
WHEN UnitPrice > 400 THEN 'Above 400.00'
WHEN UnitPrice >=300 THEN 'Between 300 and 400.00'
END
AS "Price Range"
FROM /shared/examples/ds_orders/orderdetails