Check existence of key before adding it using alter table to avoid error messages?

Posted on 2007-11-23
Last Modified: 2008-02-01
When I execute the MySQL command

ALTER TABLE `forum_reply`
     MODIFY `type` int(11),
    ADD KEY `fid` (`fid`);

it generates the error:

Error Code : 1061
Duplicate key name 'fid'

which is obvious because the same key 'fid' already exist. Is there a way to check the existence of a key before executing the ADD KEY `fid` (`fid`) command? Because some of my clients does have key created and some don't depending on the version of a script they are using and this error is really bugging me because of the overwhelming support requests I get.

Or is there a way to just ignore and force creating of a key by overwriting an exist key? Either way will solve the problem for me. Thanks.
Question by:santocki
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LVL 17

Expert Comment

ID: 20341102
create a query, and select fid
select fid from table where fid = '$fid'
execute the query,
then use the following
$resultNumber =  mysql_num_rows($queryResult)

This wil display the number of existence of fid in the table.

then make an if statement on it

if($resultNumber == 0)
/// The there is no field in the db so you can use ur code
ALTER TABLE `forum_reply`
     MODIFY `type` int(11),
    ADD KEY `fid` (`fid`);

//This means that there is ID
so just edit, the field called type
update table 'forum_reply' set type = .... where fid = '$fid'


Be sure about the variables you are using?


Author Comment

ID: 20341399
Thanks for the solution, but I am not trying to use PHP, I just wanted to know if there is a way to use pure MySQL commands, because I think I seen somewhere that somebody used the IF() command within the SQL to make some kind of decision because executing a command.

Author Comment

ID: 20341403
The reason I need pure SQL command is because I give the sql extension file for my clients to execute on their MySQL client.
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LVL 20

Expert Comment

ID: 20341541
You could check if the key existed by checking the nformation_schema.statistics table but you can not use conditional statements with alter table syntax.

The only way that this could be done is using a stored procedure.

Is this acceptable ?

Author Comment

ID: 20341692
The script they are using is MyISAM table  without views or stored procedure.
LVL 20

Expert Comment

ID: 20343249
It can not be done using a single sql statement
LVL 20

Accepted Solution

steelseth12 earned 500 total points
ID: 20343261
You could use

ALTER TABLE `forum_reply`
     MODIFY `type` int(11),
    ADD KEY  (`fid`);

But if KEY exist it will add another KEY fid_2 , fid_3 etc

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