Mysql计算字段长度函数之CHAR_LENGTH函数

CHAR_LENGTH(str)

-- 4
SELECT CHAR_LENGTH('test');
-- 12
SELECT CHAR_LENGTH('Hello World!');
-- 2
SELECT CHAR_LENGTH('小胡');
-- 3
SELECT CHAR_LENGTH('123');
-- 4
SELECT CHAR_LENGTH(',,,,');
-- 2
SELECT CHAR_LENGTH('  ');
-- 0
SELECT CHAR_LENGTH('');
-- Null
SELECT CHAR_LENGTH(NULL);

drop table if exists user_info;
CREATE TABLE user_info (
    id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID',
    uid int UNIQUE NOT NULL COMMENT '用户ID',
    `nick_name` varchar(64) COMMENT '昵称',
    achievement int COMMENT '成就值',
    level int COMMENT '用户等级',
    job varchar(32) COMMENT '职业方向',
    register_time datetime COMMENT '注册时间'
)CHARACTER SET utf8 COLLATE utf8_general_ci;
INSERT INTO user_info(uid,`nick_name`,achievement,`level`,job,register_time) VALUES
  (1001, '牛客1', 19, 0, '算法', '2020-01-01 10:00:00'),
  (1002, '牛客2号', 1200, 3, '算法', '2020-01-01 10:00:00'),
  (1003, '牛客3号♂', 22, 0, '算法', '2020-01-01 10:00:00'),
  (1004, '牛客4号', 25, 0, '算法', '2020-01-01 11:00:00'),
  (1005, '牛客5678901234号', 4000, 7, '算法', '2020-01-01 10:00:00'),
  (1006, '牛客67890123456789号', 25, 0, '算法', '2020-01-02 11:00:00');

-- 解法1
SELECT uid, IF(CHAR_LENGTH(nick_name) > 13,CONCAT(LEFT(nick_name,10),'...'),nick_name)AS nick_name
FROM user_info
WHERE CHAR_LENGTH(nick_name) > 10;
-- 解法2
SELECT uid,
       (CASE WHEN CHAR_LENGTH(nick_name) <= 13 THEN nick_name
             ELSE CONCAT(SUBSTRING(nick_name,1,10),'...')
        END)AS nick_name
FROM user_info
WHERE CHAR_LENGTH(nick_name) > 10;