大连做网站价钱,邯郸seo推广,logo免费设计在线生成标智客,在本地做装修在那个网站好多表查询:1. 笛卡尔积的形式;2. 内连接的形式:查询两个表中符合连接条件的记录;SELECT 字段名称,... FROM tbl_name1INNER JOIN tbl_name2ON 连接条件3. 外连接的形式:1).左外连接:SELECT 字段名称,... FROM tbl_name1LEFT [OUTER] JOIN tbl_name2ON 条件;//先显示左表中的全部…多表查询:1. 笛卡尔积的形式;2. 内连接的形式:查询两个表中符合连接条件的记录;SELECT 字段名称,... FROM tbl_name1INNER JOIN tbl_name2ON 连接条件3. 外连接的形式:1).左外连接:SELECT 字段名称,... FROM tbl_name1LEFT [OUTER] JOIN tbl_name2ON 条件;//先显示左表中的全部记录再去右表中查询复合条件的记录不符合的以NULL代替2).右外连接:SELECT 字段名称,... FROM tbl_name1RIGHT [OUTER] JOIN tbl_name2ON 条件;//先显示右表中的全部记录再去左表中查询复合条件的记录不符合的以NULL代替案例CREATE DATABASE IF NOT EXISTS test2 DEFAULT CHARACTER SET UTF8;USE test2;CREATE TABLE emp(id INT UNSIGNED AUTO_INCREMENT KEY,username VARCHAR(20) NOT NULL UNIQUE COMMENT 编号,age TINYINT UNSIGNED NOT NULL DEFAULT 18 COMMENT 年龄,sex ENUM(男,女,保密) NOT NULL DEFAULT 保密 COMMENT 性别,addr VARCHAR(20) NOT NULL DEFAULT 北京,depId TINYINT UNSIGNED NOT NULL COMMENT 部门对应的编号)ENGINEINNODB CHARSETUTF8;INSERT emp(username,age,depId) VALUES(king,24,1),(queen,25,2),(haha,26,1),(lily,27,1),(rose,28,3),(john,29,3);INSERT emp(username,age,depId) VALUES(测试用户,39,6);CREATE TABLE dep(id TINYINT UNSIGNED AUTO_INCREMENT KEY,depName VARCHAR(50) NOT NULL UNIQUE,depDesc VARCHAR(100) NOT NULL DEFAULT )ENGINEINNODB CHARSETUTF8;INSERT dep(depName,depDesc) VALUES(研发部,技术攻关),(JAVA部,撸JAVA代码),(WEB前端部,撸前端代码),(IOS部,撸IOS代码);//查询 emp id username age 部门名称 dep depName//笛卡尔积的形式:SELECT emp.id,emp.username,emp.age,dep.depName FROM emp,dep;//内连接的形式SELECT e.id,e.username,e.age,d.depNameFROM emp AS eINNER JOIN dep AS dON e.depIdd.id;//查询emp id username age addr dep id depName depDescSELECT e.id,e.username,e.age,e.addr,d.id,d.depName,d.depDescFROM dep AS dJOIN emp AS eON d.ide.depId;//测试左外连接SELECT e.id,e.username,e.age,d.depName,d.depDescFROM emp AS eLEFT OUTER JOIN dep AS dON e.depIdd.id;// 测试右外连接SELECT e.id,e.username,e.age,d.depName,d.depDescFROM emp AS eRIGHT JOIN dep AS dON e.depIdd.id;
