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) 1: select * f
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...
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_...
);Code language:SQL (Structured Query Language)(sql) Try it 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, ...
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...
The Oracle SQL Copilot connector don't allow column names with non-alphanumeric characters in the SELECT clause. Remove any non-alphanumeric characters from column names using an alias. Example - SELECT column_name AS columnName To manage access to the search results, you can specify one or ...
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...
Getting started guides, documentation, tutorials, architectures, and more content for Oracle products and services.
Deletes one or more lines of the SQL buffer ("*" indicates the current line). You can omit the space between DEL and n or *, but not between DEL and LAST. Enter DEL with no clauses to delete the current line of the buffer. The buffer has no command history list and does not re...