SQL实例整理

select distinct student_name from table_test_one where student_name not in 
(select distinct student_name from table_test_one where score<=80);

   
   

或者

select student_name from table_test_one group by student_name having min(score)>80;

 
 

第二种方法是group by 、min函数 结合 having的使用，w3school教程里面也提到过（在 SQL 中增加 HAVING 子句原因是，WHERE 关键字无法与合计函数一起使用）

似乎看懂了，但是还是没有自己运行一遍深刻！！！自己能动手敲一遍就更好了！ 
下面我们自己造数据，后面的例子也会用到。

建表然后倒入初始数据：

DROP TABLE IF EXISTS `table_test_one`;
CREATE TABLE `table_test_one` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `student_no` varchar(10) NOT NULL,
  `student_name` varchar(10) NOT NULL,
  `subject_no` varchar(10) NOT NULL,
  `subject_name` varchar(10) NOT NULL,
  `score` int(11) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

 
 

INSERT INTO `table_test_one` VALUES ('1', '201601', '张三', '0001', '数学', '98');
INSERT INTO `table_test_one` VALUES ('2', '201601', '张三', '0002', '语文', '66');
INSERT INTO `table_test_one` VALUES ('3', '201602', '李四', '0001', '数学', '60');
INSERT INTO `table_test_one` VALUES ('4', '201602', '李四', '0003', '英语', '78');
INSERT INTO `table_test_one` VALUES ('5', '201603', '王五', '0001', '数学', '99');
INSERT INTO `table_test_one` VALUES ('6', '201603', '王五', '0002', '语文', '99');
INSERT INTO `table_test_one` VALUES ('7', '201603', '王五', '0003', '英语', '98');

 
 

可以运行一下上面两个语句试试结果是不是你想要的。

2、删除除了id不同, 其他都相同的学生冗余信息，表如下：

答案：

delete table_test_one where id not in 
(select min(id) from table_test_one group by 
student_no, student_name, subject_no, subject_name, score);

 
 

是否有看懂？如果没能看懂的话，继续往下看：

先来造数据，题1中的数据只需要执行如下SQL就变成题2中的数据了：

update table_test_one set subject_no = '0001', subject_name = '数学' where id = 6;

 
 

然后我们先执行这个看看：

select min(id) from table_test_one group by 
student_no, student_name, subject_no, subject_name, score

 
 

这个的执行结果如下：

如果还不懂就再看看几次吧。

PS：GROUP BY 语句用于结合合计函数，根据一个或多个列对结果集进行分组。刚刚就是GROUP BY 对多列的使用场景。

3、行转列：

表数据如下：

希望查询到结果如下：

答案：

select year,
(select amount from table_test_two t where t.month = 1 and t.year = table_test_two.year) as month1,
(select amount from table_test_two t where t.month = 2 and t.year = table_test_two.year) as month2,
(select amount from table_test_two t where t.month = 3 and t.year = table_test_two.year) as month3
from table_test_two group by year;

 
 

利用group by 实现行转列，这种场景在数据统计的时候经常用到。

猿友可以造数据自己运行试试：

-- ----------------------------
-- Table structure for `table_test_two`
-- ----------------------------
DROP TABLE IF EXISTS `table_test_two`;
CREATE TABLE `table_test_two` (
  `year` int(11) NOT NULL,
  `month` int(11) NOT NULL,
  `amount` decimal(10,1) NOT NULL,
  PRIMARY KEY (`year`,`month`,`amount`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

-- ----------------------------
-- Records of table_test_two
-- ----------------------------
INSERT INTO `table_test_two` VALUES ('1991', '1', '1.1');
INSERT INTO `table_test_two` VALUES ('1991', '2', '1.2');
INSERT INTO `table_test_two` VALUES ('1991', '3', '1.3');
INSERT INTO `table_test_two` VALUES ('1992', '1', '2.1');
INSERT INTO `table_test_two` VALUES ('1992', '2', '2.2');
INSERT INTO `table_test_two` VALUES ('1992', '3', '2.3');

 
 

4、复制表( 只复制结构, 源表名：table_test_two 新表名：table_test_three)

答案：

create table table_test_three as 
select * from table_test_two where 1=2;

 
 

PS：如果需要将数据也复制过去，则上面改成where 1=1

5、复制表数据（将表 table_test_two 的数据复制到表table_test_three 里面）

答案：

insert into table_test_three (year,month,amount) 
select year,month,amount from table_test_two;

 
 

6、两张关联表，删除主表中已经在副表中没有的信息

答案：

delete from table_test_student where not exists 
(select * from table_test_class where table_test_student.class_id = table_test_class.calss_id); 

 
 

我们先造点数据吧：

-- ----------------------------
-- Table structure for `table_test_class`
-- ----------------------------
DROP TABLE IF EXISTS `table_test_class`;
CREATE TABLE `table_test_class` (
  `calss_id` int(11) NOT NULL AUTO_INCREMENT,
  `calss_name` varchar(10) CHARACTER SET utf8 NOT NULL,
  PRIMARY KEY (`calss_id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;

-- ----------------------------
-- Records of table_test_class
-- ----------------------------
INSERT INTO `table_test_class` VALUES ('1', '一班');

 
 

-- ----------------------------
-- Table structure for `table_test_student`
-- ----------------------------
DROP TABLE IF EXISTS `table_test_student`;
CREATE TABLE `table_test_student` (
  `student_id` int(11) NOT NULL AUTO_INCREMENT,
  `student_name` varchar(10) CHARACTER SET utf8 NOT NULL,
  `class_id` int(11) NOT NULL,
  PRIMARY KEY (`student_id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1;

-- ----------------------------
-- Records of table_test_student
-- ----------------------------
INSERT INTO `table_test_student` VALUES ('1', '罗国辉', '1');
INSERT INTO `table_test_student` VALUES ('2', '小宝鸽', '2');