Using variable in a LIMIT clause in MySQL - mysql

Question

I am writing a stored procedure where I have an input parameter called my_size that is an INTEGER. I want to be able to use it in a LIMIT clause in a SELECT statement. Apparently this is not supported, is there a way to work around this?
# I want something like:
SELECT * FROM some_table LIMIT my_size;
# Instead of hardcoding a permanent limit:
SELECT * FROM some_table LIMIT 100;

Answer 1

For those, who cannot use MySQL 5.5.6+ and don't want to write a stored procedure, there is another variant. We can add where clause on a subselect with ROWNUM.
SET #limit = 10;
SELECT * FROM (
SELECT instances.*,
#rownum := #rownum + 1 AS rank
FROM instances,
(SELECT #rownum := 0) r
) d WHERE rank < #limit;

Answer 2

STORED PROCEDURE
DELIMITER $
CREATE PROCEDURE get_users(page_from INT, page_size INT)
BEGIN
SET #_page_from = page_from;
SET #_page_size = page_size;
PREPARE stmt FROM "select u.user_id, u.firstname, u.lastname from users u limit ?, ?;";
EXECUTE stmt USING #_page_from, #_page_size;
DEALLOCATE PREPARE stmt;
END$
DELIMITER ;
USAGE
In the following example it retrieves 10 records each time by providing start as 1 and 11. 1 and 11 could be your page number received as GET/POST parameter from pagination.
call get_users(1, 10);
call get_users(11, 10);

Answer 3

A search turned up this article. I've pasted the relevant text below.
Here's a forum post showing an example of prepared statements letting
you assign a variable value to the limit clause:
http://forums.mysql.com/read.php?98,126379,133966#msg-133966
However, I think this bug should get some attention because I can't
imagine that prepared statements within a procedure will allow for any
procedure-compile-time optimizations. I have a feeling that prepared
statements are compiled and executed at the runtime of the procedure,
which probaby has a negative impact on efficiency. If the limit
clause could accept normal procedure variables (say, a procedure
argument), then the database could still perform compile-time
optimizations on the rest of the query, within the procedure. This
would likely yield faster execution of the procedure. I'm no expert
though.

Answer 4

I know this answer has come late, but try SQL_SELECT_LIMIT.
Example:
Declare rowCount int;
Set rowCount = 100;
Set SQL_SELECT_LIMIT = rowCount;
Select blah blah
Set SQL_SELECT_LIMIT = Default;

Answer 5

This feature has been added to MySQL 5.5.6.
Check this link out.
I've upgraded to MySQL 5.5 just for this feature and works great.
5.5 also has a lot of performance upgrades in place and I totally recommend it.

Answer 6

Another way, the same as wrote "Pradeep Sanjaya", but using CONCAT:
CREATE PROCEDURE `some_func`(startIndex INT, countNum INT)
READS SQL DATA
COMMENT 'example'
BEGIN
SET #asd = CONCAT('SELECT `id` FROM `table` LIMIT ',startIndex,',',countNum);
PREPARE zxc FROM #asd;
EXECUTE zxc;
END;

Answer 7

As of MySQL version 5.5.6, you can specify LIMIT and OFFSET with variables / parameters.
For reference, see the 5.5 Manual, the 5.6 Manual and #Quassnoi's answer

Answer 8

I've faced the same problem using MySql 5.0 and wrote a procedure with the help of #ENargit's answer:
CREATE PROCEDURE SOME_PROCEDURE_NAME(IN _length INT, IN _start INT)
BEGIN
SET _start = (SELECT COALESCE(_start, 0));
SET _length = (SELECT COALESCE(_length, 999999)); -- USING ~0 GIVES OUT OF RANGE ERROR
SET #row_num_personalized_variable = 0;
SELECT
*,
#row_num_personalized_variable AS records_total
FROM(
SELECT
*,
(#row_num_personalized_variable := #row_num_personalized_variable + 1) AS row_num
FROM some_table
) tb
WHERE row_num > _start AND row_num <= (_start + _length);
END;
Also included the total rows obtained by the query with records_total.

Answer 9

you must DECLARE a variable and after that set it. then the LIMIt will work and put it in a StoredProcedure not sure if it works in normal query
like this:
DECLARE rowsNr INT DEFAULT 0;
SET rowsNr = 15;
SELECT * FROM Table WHERE ... LIMIT rowsNr;