Details
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Type:
Bug
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Status: Closed (View Workflow)
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Priority:
Major
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Resolution: Fixed
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Affects Version/s: 10.3.21, 10.4.7
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Fix Version/s: N/A
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Component/s: Data Manipulation - Update, Documentation
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Labels:None
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Environment:Ubuntu
Description
Documentation states:
"Assignments are evaluated in left-to-right order, unless the SIMULTANEOUS_ASSIGNMENT sql_mode (available from MariaDB 10.3.5) is set, in which case the UPDATE statement evaluates all assignments simultaneously."
But it seems like the "left-to-right" evaluation is not true for multiple-table-updates. So either this is a bug or the documentation lack this information.
Example:
drop table if exists tab1; |
drop table if exists tab2; |
create table tab1 (c1 int, c2 int); |
create table tab2 (c3 int); |
insert tab1 values (1,2); |
insert tab2 values (0); |
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-- first we make a multiple-table update:
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update tab1, tab2 set c1 = c2, c2 = c1; |
select * from tab1; |
/*
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output:
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+------+------+
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| c1 | c2 |
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+------+------+
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| 2 | 1 |
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+------+------+
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If evalutation was left-to-right, then the result should be "2" in both columns, but it seems like this statement "evaluates all assignments simultaneously".
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*/
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-- and now a single-table update:
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update tab1 set c1 = c2, c2 = c1; |
select * from tab1; |
/* output:
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+------+------+
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| c1 | c2 |
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+------+------+
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| 1 | 1 |
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+------+------+
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Here evalutation is "left-to-right".
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*/ |