SQL SQL中Top和Limit关键字的区别
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Difference between Top and Limit Keyword in SQL
提问by reggie
A quick Question. Suppose I have the following two queries:
一个快速的问题。假设我有以下两个查询：
SELECT TOP 2 * FROM Persons;
and
和
SELECT * FROM Persons limit 2;
I want to know the difference between the execution of the above 2 queries?
Basically, I want to know when should I use the limitkeyword and when it is appropriate to use the topkeyword.
Also, How does the database return results based on the above 2 queries.
我想知道上面2个查询的执行之间的区别？基本上，我想知道什么时候应该使用limit关键字以及什么时候使用关键字比较合适top。另外，数据库如何根据上述2个查询返回结果。
回答by Martin Smith
If you are using SQL Server use TOPif you are using MySQLor Postgresuse Limit!
如果您使用的是 SQL Server，请使用TOPif you are usingMySQL或Postgresuse Limit!
AFAIK there is no product that currently supports both. Here's onelist of current implementations and here's another(covers more products but in less detail)
回答by rene
As stated in my comment for Martin Smith's answer above, there are products that support both, LIMITand TOP(as you can see here). The difference is that TOPonly selects the first n records, but LIMITallows the definition of an offset to retrieve a specific range of records:
正如我在上面马丁·史密斯的回答评论说，有支持的产品，LIMIT以及TOP（因为你可以看到这里）。不同之处在于TOP只选择前 n 条记录，但LIMIT允许定义偏移量来检索特定范围的记录：
SELECT * FROM ... LIMIT 5 OFFSET 10
This statement selects the first 5 records, after skipping 10 records and this isn't possible with TOP.
此语句在跳过 10 条记录后选择前 5 条记录，而TOP.
The example I posted is only checked against the DBS I linked above. I didn't check a SQL standard, because of a lack of time.
我发布的示例仅针对我上面链接的 DBS 进行了检查。由于时间不够，我没有检查 SQL 标准。
回答by Chris Harrod
TOP & LIMIT both work on amazon Redshift
TOP & LIMIT 都在亚马逊 Redshift 上工作
回答by Andomar
limitworks on MySQL and PostgreSQL, topworks on SQL Server, rownumworks on Oracle.
limit适用于 MySQL 和 PostgreSQL，top适用于 SQL Server，rownum适用于 Oracle。
回答by Fire Knight
There is no difference. The TOPand LIMITkeywords function identically, and will return the same thing.
没有区别。在TOP与LIMIT关键字相同的功能，并且将返回相同的事情。
回答by Talpa
one big mistake, LIMIT is slowly because select is return full and then database server return only limited data. When it is posible used to TOP.
一个大错误，LIMIT 很慢，因为选择返回完整，然后数据库服务器只返回有限的数据。当它可能用于TOP。
