SQL> alter table if exists t1 add (id number); alter table if exists t1 add (id number) * ERROR at line 1: ORA-01430: column being added already exists in table SQL> CREATE OR REPLACE We can't mixCREATE OR REPL
in 是把外表和内表作hash 连接,而exists是对外表作loop循环,每次loop循环再对内表进行查询。 一直以来认为exists比in效率高的说法是不准确的。 如果查询的两个表大小相当,那么用in和exists差别不大。 如果两个表中一个较小,一个是大表,则子查询表大的用exists,子查询表小的用in: 例如:表A(小表),表B(大...
The syntax for the EXISTS condition in Oracle/PLSQL 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 condition will be me...
When you write EXISTS in a where clause,you're telling the optimizer that you want the outer query to be run first, using each value tofetch a value from the inner query. In many cases, EXISTS is better because itrequires you to specify a join condition, which can invoke an INDEX scan...
SELECT ID,NAME FROM A WHERE ID NOT IN (SELECT AID FROM B) 下面是普通的用法: SQL中IN,NOT IN,EXISTS,NOT EXISTS的用法和差别: IN:确定给定的值是否与子查询或列表中的值相匹配。 IN 关键字使您得以选择与列表中的任意一个值匹配的行。
Oracle Null 与 in, exists 的关系说明(not in 查不到结果),同事说查询遇到一个奇怪的事,2个表进行notin操作没有返回结果,正常情况下应该是有返回的。 一.问题重现一般来说,问题能重现就是好消息,最怕不能重现。 SQL>connscott/tiger;Connected.SQL>descemp Name
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. ...
Oracle EXISTS vs. IN# TheEXISTSoperator stops scanning rows once the subquery returns the first row because it can determine the result whereas theINoperator must scan all rows returned by the subquery to conclude the result. Additionally theINclause can’t compare anything withNULLvalues, but th...
The UseExistsForSubQuery field user property determines the type of SQL clause that Siebel CRM uses if it encounters an EXISTS search specification in a business component. If it encounters an EXISTS search specification, and if the value for this user property is: TRUE. Siebel CRM uses the ...
SQL/JSON condition json_exists lets you use a SQL/JSON path expression as a row filter, to select rows based on the content of JSON documents. You can use condition json_exists in a CASE expression or the WHERE clause of a SELECT statement. Condition json_exists checks for the existence...