mysql select 1

+----------+------------+--------------------------------+ | Query_ID | Duration | Query | +----------+------------+--------------------------------+ | 1 | 0.00017700 | select 1 | | 2 | 0.00013400 | select 1 from smily_test | | 3 | 0.00011000 | select id from smily_test | | 4 | 0.00010500 | select version from smily_test | | 5 | 0.00011700 | select * from smily_test | +----------+------------+--------------------------------+ 5 rows in set (0.00 sec)

作用上来说是没有差别的，都是查看是否有记录，一般是作条件用的.

看得出执行效率为：  select 1 > select 1 from table > select anycolum from table > select * from table 

再来看看 count(*) 和 count(1)的效率。

+----------+------------+------------------------------------+
| Query_ID | Duration   | Query                              |
+----------+------------+------------------------------------+
|        7 | 0.00037200 | select count(1) from smily_test    |
|        8 | 0.00034500 | select count(*) from smily_test    |
+----------+------------+------------------------------------+

 

mysql select 1

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