MySQL判断查询，拼接查询实战
测试一
事前准备：实例用的表结构和数据
/*
Navicat MySQL Data Transfer
Source Server : work
Source Server Version : 50616
Source Host : localhost:3306
Source Database : souvc
Target Server Type : MYSQL
Target Server Version : 50616
File Encoding : 65001
Date: 2018-03-08 18:19:18
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int(11) NOT NULL,
`name` varchar(255) DEFAULT NULL,
`state` tinyint(4) DEFAULT NULL,-- 1:有效;2:无效
`type` tinyint(4) DEFAULT NULL,-- 1:普通员工;2:中层员工;3:高层员工
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('1', '张三', '1', '1');
INSERT INTO `user` VALUES ('2', '李四', '1', '2');
INSERT INTO `user` VALUES ('3', '王五', '2', '3');
INSERT INTO `user` VALUES ('4', '赵六', '2', '2');
一、case when 函数
语法1:
CASE fieldname
WHEN value1 THEN result1
WHEN value2 THEN result2
WHEN value3 THEN result3
……
ELSE defaultresult
END实例1:
SELECT
`id` '用户ID',
`name` '用户名称',
(
CASE `state`
WHEN 1 THEN '正常'
WHEN 2 THEN '不正常'
ELSE NULL
END
) '用户状态'
FROM
`user`结果1:
语法2：
CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
WHEN condition3 THEN result3
……
ELSE defaultresult
END实例2:
SELECT
`id` '用户ID',
`name` '用户名称',
(
CASE
WHEN `state`=1 THEN '正常'
WHEN `state`=2 THEN '不正常'
ELSE NULL
END
) '用户状态'
FROM
`user`结果2
二、if函数
case when 函数处理复杂逻辑判断比较常用，如果只是处理一次判断，更简单的方式是IF函数
语法：
IF(condition,result1,result2)实例:
SELECT
`id` '用户ID',
`name` '用户名称',
IF(state=1,'正常','不正常') '用户状态'
FROM
`user`结果：
三、elt函数
语法：
ELT(condition,result1,result2,result3,...)注意：condition的值必须是顺序1、2、3、...才会对应结果result1、result2、result3、...
实例：
SELECT
`id` '用户ID',
`name` '用户名称',
`type`,
ELT(type,'普通员工','中层员工','高层员工') '用户类型'
FROM
`user`;结果：
实战
问题描述，计算19年前三个月与18年前三个月销售数据的同比增长率。
并将增长率正负用字段type区分开来。
注意：由于数据量不大，为方便所以使用select * from查询，一般数据量大最好是一个一个把字段输入
SELECT
*,
IF (增长率 > 0, '1', '2') AS type
FROM
(
SELECT
*, (
(`b`.`money2` - `a`.`money1`) / `a`.`money1`
) AS `增长率`
FROM
(
SELECT
`省份` AS `省份1`,
sum(`结算金额`) AS money1
FROM
`销售表2018`
WHERE
date_format(单据日期, '%Y-%m') = "2018-01"
OR date_format(单据日期, '%Y-%m') = "2018-02"
OR date_format(单据日期, '%Y-%m') = "2018-03"
GROUP BY
`省份1`
) AS a
LEFT JOIN (
SELECT
`省份` AS `省份2`,
sum(`结算金额`) AS money2
FROM
`销售表2019`
WHERE
date_format(单据日期, '%Y-%m') = "2019-01"
OR date_format(单据日期, '%Y-%m') = "2019-02"
OR date_format(单据日期, '%Y-%m') = "2019-03"
GROUP BY
`省份2`
) AS b ON a.`省份1` = b.`省份2`
) AS c部分原始数据1：
结果1：
最后与经纬度表格连接起来读取，并将两个字段内容做拼接。
部分原始数据2：
SELECT *,concat('19年1-3月总结算金额:',总结算金额,'\n。同比18年1-3月增长率为:',增长率) as info FROM
(SELECT * from 2019销售表含地图) as e
LEFT JOIN
(SELECT
*,
IF (增长率 > 0, '1', '2') AS type
FROM
(
SELECT
*, (
(`b`.`money2` - `a`.`money1`) / `a`.`money1`
) AS `增长率`
FROM
(
SELECT
`省份` AS `省份1`,
sum(`结算金额`) AS money1
FROM
`销售表2018`
WHERE
date_format(单据日期, '%Y-%m') = "2018-01"
OR date_format(单据日期, '%Y-%m') = "2018-02"
OR date_format(单据日期, '%Y-%m') = "2018-03"
GROUP BY
`省份1`
) AS a
LEFT JOIN (
SELECT
`省份` AS `省份2`,
sum(`结算金额`) AS money2
FROM
`销售表2019`
WHERE
date_format(单据日期, '%Y-%m') = "2019-01"
OR date_format(单据日期, '%Y-%m') = "2019-02"
OR date_format(单据日期, '%Y-%m') = "2019-03"
GROUP BY
`省份2`
) AS b ON a.`省份1` = b.`省份2`
) AS c) as d
ON e.省份=d.省份1
结果2：
待续