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CASE 的介绍
Case 具有两种格式,简单的Case函数和Case搜索函数
简单的Case函数:
创建一张表并且添加数据:
/*
Navicat MySQL Data Transfer
Source Server : MyDB
Source Server Version : 50720
Source Host : localhost:3306
Source Database : student
Target Server Type : MYSQL
Target Server Version : 50720
File Encoding : 65001
Date: 2018-11-01 16:42:00
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for person
-- ----------------------------
DROP TABLE IF EXISTS `person`;
CREATE TABLE `person` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`sex` int(2) DEFAULT NULL,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of person
-- ----------------------------
INSERT INTO `person` VALUES ('1', '1', '王');
INSERT INTO `person` VALUES ('2', '2', '张');
SQL示例:
SELECT
p.id,
p. NAME,
CASE p.sex
WHEN 1 THEN
"男"
WHEN 2 THEN
"女"
ELSE
"第三性别"
END sex
FROM
person p
查询结果:
CASE搜索函数:
示例数据表:
/*
Navicat MySQL Data Transfer
Source Server : MyDB
Source Server Version : 50720
Source Host : localhost:3306
Source Database : student
Target Server Type : MYSQL
Target Server Version : 50720
File Encoding : 65001
Date: 2018-11-01 16:56:42
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for courses
-- ----------------------------
DROP TABLE IF EXISTS `courses`;
CREATE TABLE `courses` (
`courseno` varchar(20) NOT NULL,
`coursenm` varchar(100) NOT NULL,
PRIMARY KEY (`courseno`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='课程表';
-- ----------------------------
-- Records of courses
-- ----------------------------
INSERT INTO `courses` VALUES ('C001', '大学语文');
INSERT INTO `courses` VALUES ('C002', '新视野英语');
INSERT INTO `courses` VALUES ('C003', '离散数学');
INSERT INTO `courses` VALUES ('C004', '概率论与数理统计');
INSERT INTO `courses` VALUES ('C005', '线性代数');
INSERT INTO `courses` VALUES ('C006', '高等数学(一)');
INSERT INTO `courses` VALUES ('C007', '高等数学(二)');
CASE 搜索查询语句
SELECT
MAX(
CASE
WHEN c.courseno = 'C001' THEN
'大学语文'
ELSE
'其他'
END
) 'yuwei',
MAX(
CASE
WHEN c.courseno = 'C001' THEN
'新视野英语'
ELSE
'其他'
END
) 'yingyu'
FROM
courses c
查询结果: