基础查询

//查询常量
SELECT 100;
SELECT ‘Mike‘;

#查询表达式
SELECT 100%98;

#查询函数
SELECT VERSION();

#起别名
SELECT 100%98 AS result;

SELECT
last_name AS 姓,
first_name AS 名
FROM
employees;

SELECT
last_name 姓,
first_name 名
FROM
employees;

SELECT salary AS "out put" FROM employees;

#去重
SELECT department_id FROM employees; #有重复的部门编号
SELECT DISTINCT department_id FROM employees;

#+号的作用
/*
只有运算符功能
*/
SELECT last_name+first_name AS 姓名 FROM employees;

#拼接 concat
SELECT CONCAT(last_name,‘ ‘, first_name) AS 姓名 FROM employees;

基础查询

原文：https://www.cnblogs.com/qseven/p/15153847.html