Mysql 常用语句实战（1）

DROP TABLE IF EXISTS `emp`;
CREATE TABLE `emp`  (
  `id` int(11) NOT NULL COMMENT '员工编号',
  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '员工姓名',
  `dept_id` int(11) NULL DEFAULT NULL COMMENT '部门编号',
  `leader` int(11) NULL DEFAULT NULL COMMENT '直属领导id',
  `is_enable` int(11) NULL DEFAULT NULL COMMENT '是否在职 1在职 0离职',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;


INSERT INTO `emp` VALUES (1, '张三丰', 1, 0, 1);
INSERT INTO `emp` VALUES (2, '张无忌', 1, 1, 1);
INSERT INTO `emp` VALUES (3, '小龙女', 1, 1, 1);
INSERT INTO `emp` VALUES (4, '小白菜', 1, 3, 1);
INSERT INTO `emp` VALUES (5, '韦小宝', 2, 0, 1);
INSERT INTO `emp` VALUES (6, '令狐冲', 2, 0, 1);
INSERT INTO `emp` VALUES (7, '东方不败', 0, 8, 1);
INSERT INTO `emp` VALUES (8, '任我行', 3, 0, 1);
INSERT INTO `emp` VALUES (9, '李寻欢', 0, 8, 1);


DROP TABLE IF EXISTS `dept`;
CREATE TABLE `dept`  (
  `id` int(11) NOT NULL COMMENT '部门id',
  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '部门名称',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;

INSERT INTO `dept` VALUES (1, '销售部');
INSERT INTO `dept` VALUES (2, '信息技术部');
INSERT INTO `dept` VALUES (3, '财务部');
INSERT INTO `dept` VALUES (4, '有关部门');

-- 1、查询张姓员工的员工信息和所在部门信息。
select * from emp e left join dept d on e.dept_id=d.id where e.`name` like "%张%";

-- 2、查询张三丰管理了几个员工
select e1.name,count(1) as "手下数量" from emp e1 inner join emp e2 on e1. id = e2.leader where e1.`name` = "张三丰";

-- 3、查询出所有实习员工（实习员工无部门信息）
select * from emp e where e.dept_id not in (select id from dept)
select * from emp e left join dept d on e.dept_id = d.id where d.name is null

-- 4、查询每个部门有多少个员工，并打印部门名字、部门里的所有员工名字
select d.id,d.name,count(1),group_concat(e.name) from emp e right join dept d on e.dept_id = d.id group by d.id