2: select * from B where cc in (select cc from A) 效率高,用到了B表上cc列的索引; select * from B where exists(select cc from A where cc=B.cc) 效率低,用到了A表上cc列的索引。 not in 和not exists 如果查询语句使用了not in 那么内外表都进行全表扫描,没有用到索引; 而not extsts ...
SQL server的Exist与in区别 Exists:将外查询表的每一行,代入内查询作为检验,如果内查询返回的结果取非空值,则EXISTS子句返回TRUE,这一行行可作为外查询的结果行,否则不能作为结果。 区别: IN表是外边和内表进行hash连接,是先执行子查询。 EXISTS是对外表进行循环,然后在内表进行查询。 适用范围: 当查询字段进行了...
select max(id) as id from uplogdel group by tablename这句查询的结果就一个，就是最大的id，不用not in就可以，也不用not exist，直接这样写：select * from uplogdel where id < (select max(id)as id from uplogdel group by tablename)
4 restart the SQL Server service. (net stop MSSqlServer stops service under DOS or command line, and net start MSSqlServer starts service, which is also a shortcut.). Note: in connection with the local server, usually use the named pipes protocol (in the server network utility can be ...
在SQL Server 中,IF NOT EXISTS 是一个非常有用的条件语句,它允许开发者在尝试执行某些操作之前,检查特定的数据库对象(如表、视图、索引等)是否存在。下面是对 IF NOT EXISTS 的详细解释及其在不同场景中的应用。 1. 解释 SQL Server 中 "IF NOT EXISTS" 的用途 IF NOT EXISTS 主要用于条件判断,确保在继续...
The udl file is stored on the server and used for testing all client's connectivity. Error is "Test connection failed because of an error in initializing provider. [DBNETLIB] [ConnectionOpen (Connect()).]SQL Server does not exist or access is denied" The new workstation successfully connects...
IN:适用于子查询返回结果集较小时,因为它会将子查询的结果与主查询的条件进行逐一对比。如果主查询的条件在子查询的结果集中存在,则条件成立;否则不成立。 类型 EXISTS:是一种存在性判断,只关心子查询是否有结果返回。 IN:是一种集合匹配,关心子查询返回的结果是否与主查询的条件匹配。 应用场景 使用EXISTS的场景:...
307255 Component Checker: Diagnose problems and reconfigure MDAC installations • Check the protocol that is specified in the following subkey: HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/MSSQLServer/Client/ConnectTo/DSQUERY This value typically reflects the settings in the CNU, but sometimes it does not....
SQL Server is running SQL Server does not exist or unavailable Remote connection is disabled for SQL instance Port is not added in the firewall exception list IP address of the instance is blocked Make sure the user has permission to access to SQL and password is correct. ...
Error message: [DBNETLIB]SQL Server does not exist or access denied. MSDEWriter uses MDAC SQLOLEDB to make connections to all SQL instances installed on a machine. VSS finds SQL server instances and the instance names by enumrating running SQL server services on the box. It uses the ...