How does mysql obtain the total number of records of a group by statement?

Many of you know that you can only use group by to count the number of groups but not the amount of data. Some may use count to count the number of groups. In fact, you can configure group by SQL _CALC_FOUND_ROWS for the instance.

Mysql can obtain the total number of record groups in a field within the group by statement, but cannot count the number of records in the group.

Mysql SQL _CALC_FOUND_ROWS writes the following statements in many paging programs:

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Select count (*) from 'table' WHERE ......;

Total number of records that meet the criteria

 

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SELECT * FROM 'table' WHERE... limit M, N;

To query the data to be displayed on the page, you can change the statement:

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SELECT SQL _CALC_FOUND_ROWS * FROM 'table' WHERE... limit M, N; SELECT FOUND_ROWS ();

Therefore, it can be implemented with the SQL _CALC_FOUND_ROWS and FOUND_ROWS () functions provided by mysql.

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SELECT SQL _CALC_FOUND_ROWS t3.id, a, bunch, of, other, stuff FROM t1, t2, t3 WHERE (associate t1, t2, and t3 with each other) GROUPBY t3.id LIMIT 10, 20 SELECT FOUND_ROWS () as count;

Use the preceding two statements to complete the total number of records that meet the requirements of group.

Appendix:

Simple use of group:

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'Select column_id, count (*) as count FROM my_table group by column_id ';