MySql中group_concat的使用

CREATE TABLE `staff` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) NULL DEFAULT NULL COMMENT '姓名',
`salary` BIGINT(20) NULL DEFAULT NULL COMMENT '薪水',
`depart` VARCHAR(50) NULL DEFAULT NULL COMMENT '部门',
PRIMARY KEY (`id`)
)
COMMENT='职工表'
ENGINE=InnoDB;

INSERT INTO `staff` (`id`, `name`, `salary`, `depart`) VALUES (1, '小李', 5000, 'it部门');
INSERT INTO `staff` (`id`, `name`, `salary`, `depart`) VALUES (3, '小红', 3000, '人事');
INSERT INTO `staff` (`id`, `name`, `salary`, `depart`) VALUES (2, '张三', 2000, '财务');

以下有几种查询sql:
1、select a.depart, sum(a.salary) from staff a group by a.depart;


2、select a.depart, concat("price=" , sum(a.salary)) from staff a group by a.depart;

3、select a.depart, group_concat("depart=",a.depart, ",price=", sum(a.salary)) from staff a group by a.depart;

4、以上可以更改为：

select group_concat("depart=",c.depart, " price=",c.result) from staff a leftjoin (select b.depart, sum(b.salary) as result from staff b group by b.depart) as c on c.depart = a.depart;

在网上看到一种说法：The SUM and AVG functions are not procedural. They are done in parallel. Which means that they can't be dependent.

总结一下，a、对于group_concat中使用聚合函数的情况，可以选择先计算聚合函数，再引用。b、可以对查询结果取别名