今天在做项目的时候有一个地方需要用到嵌套查询,之前实现过类似的功能,但是在某些地方看到过类似的实现思路,自己试着实现了下发现行得通,于是就有了本文
首先是数据库,在这里我新建了两张表,一张用户表,一张课程表,具体如下
## 用户表
CREATE TABLE `test_user` (
`id` int NOT NULL AUTO_INCREMENT,
`username` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '用户名',
`age` int NULL DEFAULT NULL COMMENT '年龄',
`gender` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '性别',
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
## 课程表
CREATE TABLE `test_class` (
`id` int NOT NULL AUTO_INCREMENT,
`class_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '课程名',
`class_code` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '课程编码',
`user_id` int NULL DEFAULT NULL COMMENT '用户id',
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 CO