[#MDEV-8792] Check if it's Ok for Item_func_nullif to have two args[x] refer to the same Item

[MDEV-8792] Check if it's Ok for Item_func_nullif to have two args[x] refer to the same Item Created: 2015-09-11 Updated: 2017-05-30 Resolved: 2017-05-30
Status:	Closed
Project:	MariaDB Server
Component/s:	OTHER
Fix Version/s:	N/A

Type:

Task

Priority:

Minor

Reporter:

Alexander Barkov

Assignee:

Alexander Barkov

Resolution:

Won't Fix

Votes:

Labels:

None

Description

Item_func_nullif does this trick:

  // Put "a" to args[0] for comparison and to args[2] for the returned value.

  Item_func_nullif(THD *thd, Item *a, Item *b):

    Item_func_hybrid_field_type(thd, a, b, a)

{}

to emulate CASE WHEN a=b THEN NULL ELSE a END

It seems to work fine, but needs theoretical proves that it's OK to do this way.

Comments

Comment by Sergei Golubchik [ 2017-05-30 ]

Checked. Not OK.

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