Appendix B: MySQL Functions - Build Your Own DatabaseDriven Website Using PHP amp;amp; MySQL [Electronic resources] نسخه متنی

IFNULL(expr1,expr2)

This function returns expr1 unless it is NULL,
in which case it returns expr2.

NULLIF(expr1,expr2)

This function returns expr1 unless it equals expr2,
in which case it returns NULL.

IF(expr1,expr2,expr3)

If expr1 is TRUE (that is, not NULL or 0),
returns expr2; otherwise, returns expr3.

CASE value

WHEN [compare-value1]
THEN result1

[WHEN ...] [ELSE else-result]
END

This function returns result1 when value=compare-value1 (note
that several compare-value/result pairs can be defined); otherwise, returns else-result,
or NULL if none is defined.

CASE WHEN [condition1]
THEN

result1 [WHEN ...] [ELSE

else-result]
END

This function returns result1 when condition is TRUE (note
that several condition/result pairs can be defined); otherwise, returns else-result,
or NULL if none is defined.