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Limit has variable limits workaround needed?

Posted on 2008-06-20
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Last Modified: 2011-07-08
Seem like I cannot use a variable in a limit clause like so: Limit @rowcount

Is there any workaround for the following syntax?

select @row_count = (Select colRows from tbltemp where colName = 'table1');
set @adj_row_count = (@row_count *.5);

INSERT INTO table2 (col1, col2) Select col1, col2 FROM table1 Limit @adj_row_count

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Question by:kvnsdr
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2 Comments
 
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Accepted Solution

by:
Rurne earned 2000 total points
ID: 21833920
You're going to need to create a user function to replicate this.  @variables are not allowed in straightforward SQL in MySQL. See:
http://bugs.mysql.com/bug.php?id=11918
http://bugs.mysql.com/bug.php?id=8094

The alternative is to create a stored procedure and call it instead (e.g., "CALL variable_insert();").  Try:
CREATE PROCEDURE variable_insert()
BEGIN
DECLARE row_count, adj_row_count INT;
SELECT colRows INTO row_count FROM tbltemp WHERE colName = 'table1';
set @adj_row_count = row_count / 2;
 
INSERT INTO table2 (col1, col2) SELECT col1, col2 FROM table1 LIMIT adj_row_count;
END;

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Expert Comment

by:CMDAI
ID: 36151068
Im posting this for people like me who spent ages looking for an easy workaround for limit @variable
# THIS WILL FAIL
select * from some_table limit @a ;

#Instead use this work around
@a=0;
select * from some_table where (@a := @a +1) < @your_limit;

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