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SQL Language Extension: COALESCE

Function:
Allow a column value to be calculated by a number of expressions,
the first expression returning a non NULL value is returned as the
column value

Author:
Arno Brinkman <firebird@abvisie.nl>

Format:

<case abbreviation> ::=
| COALESCE <left paren> <value expression> { <comma> <value expression> }... <right paren>


Syntax Rules:
1) COALESCE (V1, V2) is equivalent to the following <case specification>:
CASE WHEN V1 IS NOT NULL THEN V1 ELSE V2 END
2) COALESCE (V1, V2,..., Vn), for n >= 3, is equivalent to the following
<case specification>:
CASE WHEN V1 IS NOT NULL THEN V1 ELSE COALESCE (V2,...,Vn) END

Notes:
See also README.data_type_results_of_aggregations.txt

Examples:
A)

SELECT
PROJ_NAME AS Projectname,
COALESCE(e.FULL_NAME,'[> not assigned <]') AS Employeename
FROM
PROJECT p
LEFT JOIN EMPLOYEE e ON (e.EMP_NO = p.TEAM_LEADER)

B)
SELECT
COALESCE(Phone,MobilePhone,'Unknown') AS "Phonenumber"
FROM
Relations

Соседние файлы в папке sql.extensions