什么叫连接列

1 USE [pratice]
2 GO
3 SELECT * FROM [dbo].[ddl_log] WHERE [Event]+[LoginName]='CREATE_TABLEJOE\Administrator'
4 
5 SELECT * FROM [dbo].[ddl_log] WHERE [Event]='CREATE_TABLE' AND [LoginName]='JOE\Administrator'

什么叫连接列

[Event]+[LoginName]='CREATE_TABLEJOE\Administrator' 就表示连接列

连接列是不会走索引的，所以写SQL语句的时候要慎用

最好改写为下面这样

[Event]='CREATE_TABLE' AND [LoginName]='JOE\Administrator'

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