数据函数
SELECT ABS(-8);
SELECT CEILING(9.4);
SELECT FLOOR(9.4);
SELECT RAND();
SELECT SIGN(0);
字符串函数
SELECT CHAR_LENGTH('坚持就能成功');
SELECT CONCAT('我','爱','程序');
SELECT INSERT('我爱编程helloworld',1,2,'超级热爱');
SELECT LOWER('KuangShen');
SELECT UPPER('KuangShen');
SELECT LEFT('hello,world',5);
SELECT RIGHT('hello,world',5);
SELECT REPLACE('坚持就能成功','坚持','努力');
SELECT SUBSTR('坚持就能成功',4,6);
SELECT REVERSE('坚持就能成功'); /*反转
SELECT REPLACE(studentname,'周','邹') AS 新名字
FROM student WHERE studentname LIKE '周%';
日期和时间函数
SELECT CURRENT_DATE();
SELECT CURDATE();
SELECT NOW();
SELECT LOCALTIME();
SELECT SYSDATE();
SELECT YEAR(NOW());
SELECT MONTH(NOW());
SELECT DAY(NOW());
SELECT HOUR(NOW());
SELECT MINUTE(NOW());
SELECT SECOND(NOW());
系统信息函数
SELECT SYSTEM_USER()
SELECT USER()
SELECT VERSION();