Postgresql LIMIT and OFFSET

LIMIT and OFFSET allow you to retrieve just a portion of the rows that are generated by the rest of the query:

SELECTselect_listFROMtable_expression[LIMIT {number| ALL }] [OFFSETnumber]

If a limit count is given, no more than that many rows will be returned (but possibly less, if the query itself yields less rows). LIMIT ALL is the same as omitting the LIMIT clause.

OFFSET says to skip that many rows before beginning to return rows. OFFSET 0 is the same as omitting the OFFSET clause. If both OFFSET and LIMIT appear, then OFFSET rows are skipped before starting to count the LIMIT rows that are returned.

When using LIMIT, it is important to use an ORDER BY clause that constrains the result rows into a unique order. Otherwise you will get an unpredictable subset of the query‘s rows. You may be asking for the tenth through twentieth rows, but tenth through twentieth in what ordering? The ordering is unknown, unless you specified ORDER BY.

The query optimizer takes LIMIT into account when generating a query plan, so you are very likely to get different plans (yielding different row orders) depending on what you give for LIMIT and OFFSET. Thus, using different LIMIT/OFFSET values to select different subsets of a query result will give inconsistent results unless you enforce a predictable result ordering with ORDER BY. This is not a bug; it is an inherent consequence of the fact that SQL does not promise to deliver the results of a query in any particular order unless ORDER BY is used to constrain the order.

The rows skipped by an OFFSET clause still have to be computed inside the server; therefore a large OFFSET can be inefficient.

时间： 2024-10-29 13:48:47

Postgresql LIMIT and OFFSET的相关文章

Sqlite中的limit和offset的用法

在Sqlite3中没用top语法的结构,Sqlite3中是用limit来实现这样的功能的.mytable表中的数据如下:idvalue1&n.. 在Sqlite3中没用top语法的结构,Sqlite3中是用limit来实现这样的功能的. mytable表中的数据如下: id    value 1    hello 2    你们 3    你们 4    Very Good 5    ! 如下SQL语句:select * from mytable limit 3;显示的查询结果是: 1    h

jdk8 stream实现sql单表select a,b,sum(),avg(),max() from group by a,b order by a,b limit M offset N及其性能

之所以要测该场景,是因为merge多数据源结果的时候,有时候只是单个子查询结果了,而此时采用sql数据库处理并不一定能够合理(网络延迟太大). 测试数据10万行,结果1000行 limit 20 offset 0的延时如下: package com.hundsun.ta.base.service; import com.hundsun.ta.utils.JsonUtils; import lombok.AllArgsConstructor; import lombok.NoArgsConstru

mysql limit和offset用法

limit和offset用法 mysql里分页一般用limit来实现 1. select* from article LIMIT 1,3 2.select * from article LIMIT 3 OFFSET 1 上面两种写法都表示取2,3,4三条条数据 当limit后面跟两个参数的时候,第一个数表示要跳过的数量,后一位表示要取的数量,例如 select* from article LIMIT 1,3 就是跳过1条数据,从第2条数据开始取,取3条数据,也就是取2,3,4三条数据 当 lim

LIMIT和OFFSET用法小结

① SELECT * FROM testtable LIMIT 2,1; ② SELECT * FROM testtable LIMIT 2 OFFSET 1; ③ SELECT * FROM testtable LIMIT 3; 注意: 1.数据库数据计算是从0开始的 2.OFFSET X是跳过X个数据,LIMIT Y是选取Y个数据 3.LIMIT  X,Y  中X表示跳过X个数据,读取Y个数据 4.当LIMIT和OFFSET组合使用的时候,LIMIT后面只能有一个参数,表示要取的的数量,OF

MySQL 中limit、offset的使用

简历表格,表格名称是user 执行如下SQL语句 SELECT * FROM `user` WHERE sex = 1 结果如下: 加入limit和offset之后,limit表示选取多少条数据,offset表示从开始的偏移量 SELECT * FROM `user` WHERE sex = 1 LIMIT 2 OFFSET 2 对应的结果如下: 参考:https://www.cnblogs.com/NullCXY/p/9860373.html 原文地址:https://www.cnblogs.

关于MySQL5.6的limit和offset在命令行执行时出现的问题的记录

//可以,从第2条记录开始向后2条 语句1:select * from test_tb1 1imit 2 offset 1;//直接手打可以用,但是粘贴不可用 语句2:select * from test_tb1 limit 1,2;//粘贴也可以用 语句1和语句2是等价的,都是返回查询结果的第2条记录开始向后2个记录,也就是第2.3条记录, 但是执行语句1的时候却出现的手打可用,从记事本复制粘贴不可用的情况.

mysql用limit时offset越大时间越长

首先说明一下MySQL的版本: mysql> select version();+-----------+| version() |+-----------+| 5.7.17    |+-----------+1 row in set (0.00 sec) 表结构: mysql> desc test;+--------+---------------------+------+-----+---------+----------------+| Field  | Type           

mysql --limit和offset区别

上图为t1表中所有数据.比如这个Sql语句从第1条数据向后取2条数据,limit 2 表示取数据的数量是两条,offset 1 表示的是从第1条数据开始取(程序的索引都是从0开始).而这个SQL,limit后面表示是从第2条开始向后取数据,取1条信息. 原文地址:http://blog.51cto.com/13659661/2160262

pagination -limit & offset (python)

(based in postgresql ) LIMIT: if a limit count is given , no more than taht many rows be returned (but possibly less, if query itself yields less rows) OFFSET: OFFSET says to skip that many rows before beginning to return rows to the client. OFFSET 0