Question

Im in a dilema on which one of these methods are most efficient.

Suppose you have a query joining multiple tables and querying thousand of records. Than, you gotta get the total to paginate throughout all these results.

Is it faster to?

1) Do a complete select (suppose you have to select 50’s columns), count the rows and than run another query with limits? (Will the MySQL cache help this case already selecting all the columns you need on the first query used to count?)

2) First do the query using COUNT function and than do the query to select the results you need.

3) Instead of using MySQL COUNT function, do the query selecting the ID’s for example and use the PHP function mysql_num_rows?

• I think the number 2 is the best option, using MySQL built in COUNT function, but I know MySQL uses cache, so, selecting all the results on first query gonna be faster?

Thanks,

Answer 1

Have a look at Found_Rows()

A SELECT statement may include a LIMIT clause to restrict the number
of rows the server returns to the client. In some cases, it is
desirable to know how many rows the statement would have returned
without the LIMIT, but without running the statement again. To obtain
this row count, include a SQL_CALC_FOUND_ROWS option in the SELECT
statement, and then invoke FOUND_ROWS() afterward:

mysql> SELECT SQL_CALC_FOUND_ROWS * FROM tbl_name WHERE id > 100 LIMIT 10;
mysql> SELECT FOUND_ROWS();

The second SELECT returns a number indicating how many rows the first SELECT`
would have returned had it been written without the LIMIT clause.