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(大表...
SELECT pub_name FROM publishers WHERE NOT EXISTS (SELECT * FROM titles WHERE pub_id =publishers.pub_id AND type = 'business') 下面的查询查找已经不销售的书的名称: SELECT title FROM titles WHERE NOT EXISTS (SELECT title_id FROM sales WHERE title_id =titles.title_id) 语法 EXISTS subquery 参...
换成exists 进行测试: SQL>select empno,ename from emp A where not exists ( SELECT * FROM emp1 Bwhere B.job = A.job); EMPNO ENAME --- 8888 Dave SQL>select empno,ename from emp A where exists ( SELECT * FROM emp1 B where B.job = A.job); EMPNO ENAME --- 7934 MILLER 7900 JAM...
);Code language:SQL (Structured Query Language)(sql) For each warehouse, the subquery checks whether its location is in the US or not. If yes, theEXISTSoperator in theWHEREclause returns true that causes the outer query to append the string', USA'to the warehouse name. Otherwise, theUPDATE...
语法:IGNORE_WHERE_CLAUSE 描述:该提示会导致优化器忽略在其之后的其它嵌入提示。在许多内部递归调用的语句(如动态采样)当中,语句中嵌入的提示都是拼接起来的。在某些情况下,Oracle不愿意一些提示其作用,该提示就会导致后续提示失效。 HELLODBA.COM>exec sql_explain('SELECT /*+ full(O) IGNORE_WHERE_CLAUSE full...
类似Python中的raw字符串: 官方解释:Use The Quote(q) operator and delimiter to allow the use of a single quotation mark with the literal character string in the SELECT clause. --- 单引号 select q'[I'm a String!]' from dual; select q'[I'''m a String!]' from dual; --- 双引号...
云数据库 SQL Server数据库sql 表结构 DROP DATABASE IF EXISTS test1; CREATE DATABASE test1; USE test1; ##部门表 #DROP IF EXISTS TABLE DEPT; CREATE TABLE DEPT( DEPTNO int PRIMARY KEY,##部门编号 DNAME VARCHAR(14) , ##部门名称 LOC VARCHAR(13) ##部门地址 ) ; INSERT INTO DEPT VALUES (10...
SQL macros and WITH clause are not known to be great friends: you cannot call a SQL macro in a WITH clause and if you want to define a table macro returning a query containing a WITH subquery(ies), then you won’t be able to use scalar parameters in this subquery. In theprevious po...
SQLFILE=[directory_object:]file_name 说明:nodefault。根据其他参数,将所有的 SQL DDL 写入指定的文件。 TABLE_EXISTS_ACTION=[SKIP | APPEND | TRUNCATE | REPLACE] 说明:default:skip(if content=data_only is specified,then the default is append) ...
PostgreSQL , Oracle , PL/SQL , 聚合函数 , 自定义聚合函数 背景 Oracle的自定义聚合函数的定义方法,在创建函数是,使用AGGREGATE USING Clause关键词。 AGGREGATE USING Clause Specify AGGREGATE USING to identify this function as an aggregate function, or one that evaluates a group of rows and returns a...