MySQL review materials (additional) case when

MySQL Review the information ( additional )case when

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MySQL Review the information ( One )——MySQL Environmental installation

MySQL Review the information ( Two )——MySQL-DDL sentence

MySQL Review the information ( 3、 ... and )——MySQL-DML sentence

MySQL Review the information ( Four )——MySQL- Aggregate functions

MySQL Review the information ( 5、 ... and )——MySQL- Indexes

MySQL Review the information ( 6、 ... and )——MySQL- Multi table joint query

MySQL Review the information ( 7、 ... and )——MySQL- stored procedure

MySQL Review the information ( 8、 ... and )——MySQL- Business

MySQL Review the information ( Nine )——MySQL- Graphical tools use

Content of this chapter ：case when Use

/*
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 Source Server         : rm-bp1zq3879r28p726lco.mysql.rds.aliyuncs.com_3306
 Source Server Type    : MySQL
 Source Server Version : 50732
 Source Host           : rm-bp1zq3879r28p726lco.mysql.rds.aliyuncs.com:3306
 Source Schema         : mytest

 Target Server Type    : MySQL
 Target Server Version : 50732
 File Encoding         : 65001

 Date: 28/06/2022 18:58:48
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for users
-- ----------------------------
DROP TABLE IF EXISTS `users`;
CREATE TABLE `users`  (
  `id` int(8) NOT NULL AUTO_INCREMENT,
  `createDate` datetime(0) NOT NULL,
  `userName` varchar(32) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  `passWord` varchar(36) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  `age` int(3) NOT NULL,
  `phone` varchar(11) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  `introduce` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  PRIMARY KEY (`id`) USING BTREE,
  INDEX `userName_index`(`userName`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 7 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of users
-- ----------------------------
INSERT INTO `users` VALUES (1, '2022-06-26 13:43:11', 'admin', '123456', 22, '15912345678', ' Like learning .');
INSERT INTO `users` VALUES (2, '2022-06-26 13:43:11', 'zhangsan', '123456', 32, '15912345678', ' I love cooking .');
INSERT INTO `users` VALUES (3, '2022-06-26 13:43:11', 'lisi', '45451', 42, '15912345678', ' I like make-up .');
INSERT INTO `users` VALUES (4, '2022-06-26 13:43:11', 'zhaoliu', '2222', 52, '15912345678', ' Like martial arts .');
INSERT INTO `users` VALUES (5, '2022-06-26 13:43:11', 'zhaoliu', '11111', 16, '15912345678', ' Like dancing .');
INSERT INTO `users` VALUES (6, '2022-06-26 13:43:11', 'zhaoliu', '123787', 27, '15912345678', ' Like to pick up girls .');

SET FOREIGN_KEY_CHECKS = 1;

test ：

Direct unsigned judgment

select userName,
(
case
when sex=0 then ' Woman '
when sex=1 then ' male '
end
) sexName
from users;

Signed judgment

select userName,age,
(
case 
when age<20 then ' teenagers '
when age<30 then ' youth '
else ' Prime of life '
end
) state
from users

Create view , And query against the view

# Query and create views 
create view newTableName as (
select userName,age,
(
case 
when age<20 then ' teenagers '
when age<30 then ' youth '
else ' Prime of life '
end
) state
from users
);
select state ' state ',count(state) ' Number '
from newTableName GROUP BY state;

Pay attention to practice .