MySQL paging query instance_ MySQL paging query example explanation "suggestions collection"

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LIMIT Clauses can be used to enforce SELECT Statement returns the specified number of records .LIMIT Accept one or two numeric parameters . Argument must be an integer constant . If two parameters are given , The first parameter specifies the offset of the first return record line , The second parameter specifies the maximum number of rows to return records . The offset of the initial record line is 0( instead of 1). below , For special cases, we are right mysql Paging query to summarize .

mysql Provide paging function ：SELECT * FROM table LIMIT [offset,] rows | rows OFFSET offset

The simplest use is ：select * from table limit ?,?

This is the simplest limit Paging query . coordination where Conditional use ：select * from table where column > ? order by id limit ?,?

This is the case above , It is suggested that column and id It is better to establish a composite index .

In both cases , For paging queries with small amounts of data , In this way sql It's enough . But for data sheets above the million level , If you use the above sql Words , The later limit The offset of the statement is getting larger and larger , Queries will become slower and slower . Be similar to ：select * from `user` where `cate`=’ shaanxi ’ order by id limit 100000,10

To avoid such queries , We can improve query efficiency by sub query .select * from `user` where id >=(select * from `user` where `cate`=’ shaanxi ’ order by id limit 100000,1) and `cate`=’ shaanxi ’ limit 10

adopt explain We can see the direct limit The gap between query and sub query ： direct limit Inquire about ：typepossible_keyskeykey_lenrefrowsExtraALL(NULL)(NULL)(NULL)(NULL)4076607 Sub query paging query :typepossible_keyskeykey_lenrefrowsExtraPRIMARYrangePRIMARYPRIMARY42038331Using where

SUBQUERYindex(NULL)PRIMARY44076663Using index

It can be seen that , Through subqueries , Subqueries are performed on the index , While ordinary queries are carried out on data files . Generally speaking , The index file is much smaller than the data file , Therefore, the operation of index files is more direct and efficient .

Besides , You can also use join Pagination SELECT * FROM `user` AS t1

JOIN (SELECT id FROM `user` ORDER BY id LIMIT 100000, 1) AS t2

WHERE t1.id <= t2.id ORDER BY t1.id LIMIT 10;

join The efficiency of paging and subquery paging is basically at one level .( however , Subqueries need to create temporary tables in memory , When the query is finished ,MySQL Need to undo these temporary tables . adopt join This can be avoided ) Before paging query , Can be judged , If it is within the limited number of pages , Just use basic paging query , Greater than, use sub query paging .

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