7.4 数据库的高级查询(❤❤)

1. 提要

2. 数据统计

2.1 聚合函数

2.2 分组查询_group by

2.3 having子句_筛选时想使用聚合函数时

3. 多表连接查询

3.1 内连接_inner join

**练习: **

3.2 外连接(左外连接)_left join

3.3 右外连接_right join

3.4 练习

3.5 小结

4. 子查询

4.1 from子查询

4.2 单行子查询与多行子查询

in,all,any,exists使用

5. SQL测试环境

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 80031
 Source Host           : localhost:3306
 Source Schema         : test

 Target Server Type    : MySQL
 Target Server Version : 80031
 File Encoding         : 65001

 Date: 16/01/2024 16:05:30
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for t_dept
-- ----------------------------
DROP TABLE IF EXISTS `t_dept`;
CREATE TABLE `t_dept`  (
  `deptno` int(0) NOT NULL COMMENT '部门编号',
  `dname` varchar(20) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL COMMENT '部门名称',
  `loc` varchar(20) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL COMMENT '部门标志',
  PRIMARY KEY (`deptno`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb3 COLLATE = utf8mb3_general_ci COMMENT = '部门表' ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of t_dept
-- ----------------------------
INSERT INTO `t_dept` VALUES (10, 'ACCOUNTING', 'NEW YORK');
INSERT INTO `t_dept` VALUES (20, 'RESEARCH', 'DALLAS');
INSERT INTO `t_dept` VALUES (30, 'SALES', 'CHICAGO');
INSERT INTO `t_dept` VALUES (40, 'OPERATIONS', 'BOSTON');

-- ----------------------------
-- Table structure for t_emp
-- ----------------------------
DROP TABLE IF EXISTS `t_emp`;
CREATE TABLE `t_emp`  (
  `empno` int(0) NOT NULL COMMENT '员工ID',
  `ename` varchar(20) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL COMMENT '姓名',
  `job` varchar(20) CHARACTER SET utf8mb3 COLLATE utf8mb3_general_ci NULL DEFAULT NULL COMMENT '职位',
  `mgr` int(0) NULL DEFAULT NULL COMMENT '领导ID',
  `hiredate` date NULL DEFAULT NULL COMMENT '入职日期',
  `sal` decimal(10, 2) NULL DEFAULT NULL COMMENT '基本工资',
  `comm` decimal(10, 2) NULL DEFAULT NULL COMMENT '绩效',
  `deptno` int(0) NULL DEFAULT NULL COMMENT '部门编号',
  PRIMARY KEY (`empno`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb3 COLLATE = utf8mb3_general_ci COMMENT = '员工表' ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of t_emp
-- ----------------------------
INSERT INTO `t_emp` VALUES (7369, 'SMITH', 'CLERK', 7902, '1980-12-17', 800.00, NULL, 20);
INSERT INTO `t_emp` VALUES (7499, 'ALLEN', 'SALESMAN', 7698, '1981-02-20', 1600.00, 300.00, 30);
INSERT INTO `t_emp` VALUES (7521, 'WARD', 'SALESMAN', 7698, '1981-02-22', 1250.00, 500.00, 30);
INSERT INTO `t_emp` VALUES (7566, 'JONES', 'MANAGER', 7839, '1981-04-02', 2975.00, NULL, 20);
INSERT INTO `t_emp` VALUES (7654, 'MARTIN', 'SALESMAN', 7698, '1981-09-28', 1250.00, 1400.00, 30);
INSERT INTO `t_emp` VALUES (7698, 'BLAKE', 'MANAGER', 7839, '1981-05-01', 2850.00, NULL, 30);
INSERT INTO `t_emp` VALUES (7782, 'CLARK', 'MANAGER', 7839, '1981-06-09', 2450.00, NULL, 10);
INSERT INTO `t_emp` VALUES (7788, 'SCOTT', 'ANALYST', 7566, '1982-12-09', 3000.00, NULL, 20);
INSERT INTO `t_emp` VALUES (7839, 'KING', 'PRESIDENT', NULL, '1981-11-17', 5000.00, NULL, 10);
INSERT INTO `t_emp` VALUES (7844, 'TURNER', 'SALESMAN', 7698, '1981-09-08', 1500.00, 0.00, 30);
INSERT INTO `t_emp` VALUES (7876, 'ADAMS', 'CLERK', 7788, '1983-01-12', 1100.00, NULL, 20);
INSERT INTO `t_emp` VALUES (7900, 'JAMES', 'CLERK', 7698, '1981-12-03', 950.00, NULL, 30);
INSERT INTO `t_emp` VALUES (7902, '田曦薇', 'ANALYST', 7566, '1981-12-03', 3000.00, NULL, 20);
INSERT INTO `t_emp` VALUES (7934, '与海', 'CLERK', 7782, '1982-01-23', 1300.00, NULL, NULL);

-- ----------------------------
-- Table structure for t_salgrade
-- ----------------------------
DROP TABLE IF EXISTS `t_salgrade`;
CREATE TABLE `t_salgrade`  (
  `grade` int(0) NOT NULL COMMENT '等级',
  `losal` decimal(10, 2) NULL DEFAULT NULL COMMENT '下限',
  `hisal` decimal(10, 2) NULL DEFAULT NULL COMMENT '上限',
  PRIMARY KEY (`grade`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb3 COLLATE = utf8mb3_general_ci COMMENT = '工资等级表' ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of t_salgrade
-- ----------------------------
INSERT INTO `t_salgrade` VALUES (1, 700.00, 1200.00);
INSERT INTO `t_salgrade` VALUES (2, 1201.00, 1400.00);
INSERT INTO `t_salgrade` VALUES (3, 1401.00, 2000.00);
INSERT INTO `t_salgrade` VALUES (4, 2001.00, 3000.00);
INSERT INTO `t_salgrade` VALUES (5, 3001.00, 9999.00);

SET FOREIGN_KEY_CHECKS = 1;