COUNT SQL 函数的性能
当使用 COUNT 函数编写 SQL 语句时，我有两种选择。
SELECT COUNT(*) FROMSELECT COUNT(some_column_name) FROM
就性能而言，最好的 SQL 语句是什么？ 使用选项 1 可以获得一些性能提升吗？
I have two choices when writing an SQL statement with the COUNT function.
SELECT COUNT(*) FROM <table_name>SELECT COUNT(some_column_name) FROM <table_name>
In terms of performance, what is the best SQL statement?
Can I obtain some performance gain by using option 1?
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性能并不重要，因为它们执行 2 个不同的聚合
COUNT(*)是所有行，包括 NULLCOUNT(some_column_name)，排除“some_column_name”中的 NULL >"有关详细信息，请参阅“Count(*) 与 Count(1)”问题
Performance should not matter because they do 2 different aggregates
COUNT(*)is all rows, including NULLsCOUNT(some_column_name), excludes NULL in "some_column_name"See the "Count(*) vs Count(1)" question for more
选项 2 实际上会计算
some_column_name不为 null 的所有字段。选项 1 对任意字段不为空的所有字段进行计数。因此，您实际上可能从这两个查询中得到不同的结果。大多数时候，您实际上想要对所有行进行计数，然后最快的选项（不检查任何字段）就是SELECT COUNT(1) FROM ...Option 2 actually counts all the fields where
some_column_nameis not null. Option 1 counts all the fields where any field is not null. So you might actually get different results out of these two queries. Most of the time you actually want to count all the rows, and then the fastest option, which does not check for any of the fields, is simplySELECT COUNT(1) FROM ...不，Sql Server 没有性能提升。
No, there is no performance gain in Sql Server.