COUNT SQL函数的性能 [英] Performance of COUNT SQL function
本文介绍了COUNT SQL函数的性能的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
使用 COUNT
函数编写SQL语句时,我有两种选择。
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>
SELECT COUNT(*) FROM <table_name>
SELECT COUNT(some_column_name) FROM <table_name>
就性能而言,最佳的SQL语句是什么?
我可以使用选项1获得一些性能提升吗?
In terms of performance, what is the best SQL statement? Can I obtain some performance gain by using option 1?
推荐答案
性能无关紧要,因为它们会进行2种不同的聚合
Performance should not matter because they do 2 different aggregates
-
COUNT(*)
是所有行,包括NULL -
COUNT(some_column_name)
,在some_column_name
$ b $中排除NULL b
COUNT(*)
is all rows, including NULLsCOUNT(some_column_name)
, excludes NULL in "some_column_name
"
请参阅 Count(*)vs Count(1)更多问题
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