比如在Northwind数据库中有一个查询为SELECT c.CustomerId,CompanyName FROM Customers c
WHERE EXISTS(
SELECT OrderID FROM Orders o WHERE o.CustomerID=c.CustomerID)这里面的EXISTS是如何运作呢?子查询返回的是OrderId字段,可是外面的查询要找的是CustomerID和CompanyName字段,这两个字段肯定不在OrderID里面啊,这是如何匹配的呢?
EXISTS用于检
SELECT 索引名称=a.name
,表名=c.name ,索引字段名=d.name ,索引字段位置=d.colid FROM sysindexes a
JOIN sysindexkeys b ON a.id=b.id AND a.indid=b.indid
JOIN sysobjects c ON b.id=c.id
JOIN syscolumns d ON b.id=d.id AND b.colid=d.colid
WHERE a.indid
复制代码 代码如下:set statistics profile on set statistics io on set statistics time on go 你执行的SQL语句 复制代码 代码如下:go set statistics profile off set statistics io off set statistics time off 执行完后点消息即可。 更多SQL内容来自千自学
标签:SQL