>Description:
The documentation for NULLIF states that expr1 is evaluated twice if the
expressions are equal.
Actually, it is the opposite. Expr1 is evaluated twice when the two exporessions
are NOT equal.
>How-To-Repeat:
mysql> set @myval:=0;
Query OK, 0 rows affected (0.00 sec)
mysql> select NULLIF(@myval:=@myval+1,1); # now @myval is 1, it matches, NULLIF
returns NULL
+----------------------------+
| NULLIF(@myval:=@myval+1,1) |
+----------------------------+
| NULL |
+----------------------------+
1 row in set (0.00 sec)
mysql> select NULLIF(@myval:=@myval+1,1); # After the first test, @myval is 2 ;
doesn't match
+----------------------------+
| NULLIF(@myval:=@myval+1,1) |
+----------------------------+
| 3 |
+----------------------------+
1 row in set (0.00 sec)
# @myval is now 3, as a result of a double evaluation, when expr1 and expr2 were not
equal.
>Fix:
Correct the documentation
>Submitter-Id: <submitter ID>
>Originator: Giuseppe Maxia
>Organization:
>MySQL support: none
>Synopsis: error in documentation
>Severity: non-critical
>Priority: low
>Category: mysql
>Class: doc-bug
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