mysql 字符串拼接+设置null值

#字符串拼接 concat(s1,s2); 将表中last_name和first_name中的字符串拼接

select concat(last_name,first_name) as  姓名 from employees;

#只会修改last_name不会修改first_name

SELECT first_name,last_name AS f FROM employees;

#将两个列用逗号隔开并命名为out_put

SELECT CONCAT(`last_name`,',',`phone_number`) AS out_put FROM employees;

#ifnull 判断是否为空,如果为空则显示为0而不是null，并将列名显示为结果

SELECT IFNULL(commission_pct,0) AS 结果 FROM employees;