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84 lines
1.6 KiB
Plaintext
84 lines
1.6 KiB
Plaintext
Function:
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Allow the result of a column to be determined by a the results of a
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case expression.
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Author:
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Arno Brinkman <firebird@abvisie.nl>
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Format:
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<case expression> ::=
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<case abbreviation>
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| <case specification>
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<case abbreviation> ::=
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NULLIF <left paren> <value expression> <comma> <value expression> <right paren>
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| COALESCE <left paren> <value expression> { <comma> <value expression> }... <right paren>
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<case specification> ::=
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<simple case>
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| <searched case>
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<simple case> ::=
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CASE <value expression>
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<simple when clause>...
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[ <else clause> ]
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END
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<searched case> ::=
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CASE
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<searched when clause>...
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[ <else clause> ]
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END
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<simple when clause> ::= WHEN <when operand> THEN <result>
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<searched when clause> ::= WHEN <search condition> THEN <result>
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<when operand> ::= <value expression>
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<else clause> ::= ELSE <result>
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<result> ::=
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<result expression>
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| NULL
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<result expression> ::= <value expression>
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Syntax Rules:
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Examples:
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A) (simple)
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SELECT
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o.ID,
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o.Description,
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CASE o.Status
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WHEN 1 THEN 'confirmed'
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WHEN 2 THEN 'in production'
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WHEN 3 THEN 'ready'
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WHEN 4 THEN 'shipped'
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ELSE 'unknown status ''' || o.Status || ''''
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END
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FROM
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Orders o
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B) (searched)
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SELECT
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o.ID,
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o.Description,
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CASE
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WHEN (o.Status IS NULL) THEN 'new'
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WHEN (o.Status = 1) THEN 'confirmed'
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WHEN (o.Status = 3) THEN 'in production'
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WHEN (o.Status = 4) THEN 'ready'
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WHEN (o.Status = 5) THEN 'shipped'
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ELSE 'unknown status ''' || o.Status || ''''
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END
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FROM
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Orders o
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