我正在推广 Django 数据库复制应用程序,它使用以下语句:
SELECT %s FROM %s LIMIT 1
获取 1 行并使用 Python DBAPI 来描述字段,它适用于 ORACLE 和 MySQL,但是,LIMIT 语句的跨平台程度如何?
最佳答案
LIMIT
已经在各种开源数据库中变得相当流行,但不幸的是,事实是 OFFSET
分页一直是所有这些数据库中标准化程度最低的 SQL 功能, 最迟在 SQL:2008 中被标准化.
在那之前,jOOQ user manual page on the LIMIT
clause显示了如何在每种 SQL 方言中形成各种等效语句:
-- MySQL, H2, HSQLDB, Postgres, and SQLite
SELECT * FROM BOOK LIMIT 1 OFFSET 2
-- CUBRID supports a MySQL variant of the LIMIT .. OFFSET clause
SELECT * FROM BOOK LIMIT 2, 1
-- Derby, SQL Server 2012, Oracle 12c, SQL:2008 standard
-- Some need a mandatory ORDER BY clause prior to OFFSET
SELECT * FROM BOOK [ ORDER BY ... ] OFFSET 2 ROWS FETCH NEXT 1 ROWS ONLY
-- Ingres
SELECT * FROM BOOK OFFSET 2 FETCH FIRST 1 ROWS ONLY
-- Firebird
SELECT * FROM BOOK ROWS 2 TO 3
-- Sybase SQL Anywhere
SELECT TOP 1 ROWS START AT 3 * FROM BOOK
-- DB2 (without OFFSET)
SELECT * FROM BOOK FETCH FIRST 1 ROWS ONLY
-- Sybase ASE, SQL Server 2008 (without OFFSET)
SELECT TOP 1 * FROM BOOK
现在,这些都非常简单,对吧?讨厌的部分来了,当你必须模仿它们时:
-- DB2 (with OFFSET), SQL Server 2008 (with OFFSET),
SELECT * FROM (
SELECT BOOK.*,
ROW_NUMBER() OVER (ORDER BY ID ASC) AS RN
FROM BOOK
) AS X
WHERE RN > 2
AND RN <= 3
-- DB2 (with OFFSET), SQL Server 2008 (with OFFSET)
-- When the original query uses DISTINCT!
SELECT * FROM (
SELECT DISTINCT BOOK.ID, BOOK.TITLE
DENSE_RANK() OVER (ORDER BY ID ASC, TITLE ASC) AS RN
FROM BOOK
) AS X
WHERE RN > 2
AND RN <= 3
-- Oracle 11g and less
SELECT *
FROM (
SELECT b.*, ROWNUM RN
FROM (
SELECT *
FROM BOOK
ORDER BY ID ASC
) b
WHERE ROWNUM <= 3
)
WHERE RN > 2
Read about the ROW_NUMBER()
vs. DENSE_RANK()
rationale here
选择你的毒药 ;-)
关于sql - SQL中的LIMIT语句有多普遍?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1528604/