使用 offset+limit 查找 mySQL 查询中的结果总数

Question

I'm doing a pagination feature using Codeigniter but I think this applies to PHP/mySQL coding in general.

I am retrieving directory listings using offset and limit depending on how many results I want per page. However to know the total number of pages required, I need to know (total number of results)/(limit). Right now I am thinking of running the SQL query a second time then count the number of rows required but without using LIMIT. But I think this seems to be a waste of computational resources.

Are there any better ways? Thanks!

EDIT: My SQL query uses WHERE as well to select all rows with a particular 'category_id'

Answer 1

看看SQL_CALC_FOUND_ROWS

Answer 2

SELECT COUNT(*) FROM table_name WHERE column = 'value' will return the total number of records in a table matching that condition very quickly.

Database SELECT operations are usually "cheap" (resource-wise), so don't feel too bad about using them in a reasonable manner.

EDIT: Added WHERE after the OP mentioned that they need that feature.

Answer 3

Considering that SQL_CALC_FOUND_ROWS requires invoking FOUND_ROWS() afterwards, if you wanted to fetch the total count with the results returned from your limit without having to invoke a second SELECT , I would use JOIN results derived from a subquery :

SELECT * FROM `table` JOIN (SELECT COUNT(*) FROM `table` WHERE `category_id` = 9) t2 WHERE `category_id` = 9 LIMIT 50

Note: Every derived table must have its own alias, so be sure to name the joined table. In my example I used t2 .

Answer 4

The SQL_CALC_FOUND_ROWS query modifier and accompanying FOUND_ROWS() function are deprecated as of MySQL 8.0.17 and will be removed in a future MySQL version. As a replacement, considering executing your query with LIMIT, and then a second query with COUNT(*) and without LIMIT to determine whether there are additional rows. For example, instead of these queries:

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

Use these queries instead:

SELECT * FROM tbl_name WHERE id > 100 LIMIT 10;
SELECT COUNT(*) WHERE id > 100;

COUNT(*) is subject to certain optimizations. SQL_CALC_FOUND_ROWS causes some optimizations to be disabled.

Answer 5

you can use 2 queries as below, One to fetch the data with limit and other to get the no of total matched rows.

Ex:

SELECT * FROM tbl_name WHERE id > 1000 LIMIT 10;
SELECT COUNT(*) FROM tbl_name WHERE id > 1000;

As described by Mysql guide , this is the most optimized way, and also SQL_CALC_FOUND_ROWS query modifier and FOUND_ROWS() function are deprecated as of MySQL 8.0.17

Answer 6

SELECT COUNT(id) FROM `table` WHERE `category_id` = 9

为您提供特定类别的行数。