MySQL Bugs: #34829: No default value for variable and setting default does not raise error

Bug #34829	No default value for variable and setting default does not raise error
Submitted:	26 Feb 2008 13:19	Modified:	13 Nov 10:42
Reporter:	Rizwan Maredia
Status:	Patch pending
Category:	Server: DML	Severity:	S3 (Non-critical)
Version:	5.1.22, 5.0.56	OS:	Microsoft Windows
Assigned to:	Sergei Golubchik	Target Version:
Tags:	system variable, default value, DEFAULT
Triage:	Triaged: D3 (Medium)

Description:
When DEFAULT is set in some of the variables, nothing happens and the last value stored
remains as it is. The following variables have shown this behavior

sql_big_tables
sql_buffer_result
sql_log_off
sql_safe_updates
sql_warnings
sql_big_selects
sql_log_bin
sql_notes
sql_quote_show_create

How to repeat:
The following source code is tested against mysql test environment.

SET @@session.sql_big_tables = 0;
SET @@session.sql_big_tables = DEFAULT;
SELECT @@session.sql_big_tables;
 
SET @@session.sql_big_tables = 1;
SET @@session.sql_big_tables = DEFAULT;
SELECT @@session.sql_big_tables;
 
Output:
SET @@session.sql_big_tables = 0;
SET @@session.sql_big_tables = DEFAULT;
SELECT @@session.sql_big_tables;
@@session.sql_big_tables
0
SET @@session.sql_big_tables = 1;
SET @@session.sql_big_tables = DEFAULT;
SELECT @@session.sql_big_tables;
@@session.sql_big_tables
1

Suggested fix:
On assigning DEFAULT either a DEFAULT value should be assigned or it should raise error
that a DEFAULT value is not associated with this variable.

Thank you for a bug report.