1. 在SQL Server中整型相除是取整(舍小数),如果要取小数且限制位数,可以用convert(numeric(10,2),a*1.0/b)或是cast(a*1.0/b as numeric(10,2))的方式得到. 2. 对于in/exists(clause)有4点需要注意: (1) 含义上来说,in/exists都是取的交集,not in/exists都是取的差集. (2) 语法
The syntax for the EXISTS condition in SQL Server (Transact-SQL) is: WHERE EXISTS ( subquery ); Parameters or Arguments subquery The subquery is a SELECT statement. If the subquery returns at least one record in its result set, the EXISTS clause will evaluate to true and the EXISTS conditio...
SQL -- Uses AdventureWorksSELECTa.LastName, a.BirthDateFROMDimCustomerASaWHEREEXISTS(SELECT*FROMdbo.ProspectiveBuyerASbWHERE(a.LastName = b.LastName)AND(a.BirthDate = b.BirthDate)) ; G. Using NOT EXISTS NOT EXISTS works as the opposite as EXISTS. The WHERE clause in NOT EXISTS is satisfied...
第一个查询使用 EXISTS 而第二个查询使用 IN。注意两个查询返回相同的信息。 USE pubs GO SELECT DISTINCT pub_name FROM publishers WHERE EXISTS (SELECT * FROM titles WHERE pub_id = publishers.pub_id AND type = 'business') GO -- Or, using the IN clause: USE pubs GO SELECT distinct pub_name...
Let us demonstrate how the SQL Server DROP TABLE IF EXISTS command performs. Assume we want to delete theperformerstable from the database. DROP TABLE IF EXISTS performers; In this example, the IF EXISTS clause checked for the table presence in the database – it was present, and the comma...
(It also seems like if SQL Server were smarter, it would execute both EXISTS clauses in parallel and let whichever one one completed first short-circuit the other.) Is there a better way to get SQL Server to consistently improve the running time of such a query? Update Thank you for you...
SQL Copy SELECT a.LastName, a.BirthDate FROM DimCustomer AS a WHERE EXISTS (SELECT * FROM dbo.ProspectiveBuyer AS b WHERE (a.LastName = b.LastName) AND (a.BirthDate = b.BirthDate)); G. Use NOT EXISTS NOT EXISTS works as the opposite as EXISTS. The WHERE clause in NOT EXISTS...
SQL SELECTa.LastName, a.BirthDateFROMDimCustomerASaWHEREEXISTS(SELECT*FROMdbo.ProspectiveBuyerASbWHERE(a.LastName = b.LastName)AND(a.BirthDate = b.BirthDate)); G. Use NOT EXISTS NOT EXISTSworks as the opposite asEXISTS. TheWHEREclause inNOT EXISTSis satisfied if no rows are returned by th...
DROP TABLE will not run because there is no row returned from sys.systables in the EXISTS clause. Option 3 – DROP TABLE if exists querying the INFORMATION_SCHEMA.TABLES View (all supported versions) We can also query the ISO compliantINFORMATION_SCHEMA.TABLESview to see if the table exists...
LEFT JOIN / IS NULLis less efficient, since it makes no attempt to skip the already matched values in the right table, returning all results and filtering them out instead. EXISTS vs JOIN and use of EXISTS clause 回答1 EXISTSis used to return a boolean value,JOINreturns a whole other tab...