mysql基础知识学习：mysql函数

一、数学函数

SELECT PI();

select ROUND(3.343535,3);

select ROUND(3.343535);

SELECT NOW();

select ABS(-90);

select CEIL(12.4);

select CEILING(12.4);

select FLOOR(12.4);

SELECT RAND();

SELECT RAND(0.3);

SELECT SIGN(3);

SELECT SIGN(-3);

SELECT SIGN(0);

SELECT TRUNCATE(3.427432,2);

SELECT ROUND(5.7);

SELECT ROUND(5.4);

SELECT POW(3.2,3);

SELECT EXP(4);

SELECT MOD(3.4,3);

SELECT log(3);

SELECT LOG10(100);

select RADIANS(60);

SELECT DEGREES(3.14);

SELECT SIN(RADIANS(30));

SELECT ASIN(RADIANS(30));

SELECT COS(RADIANS(30));

SELECT ACOS(RADIANS(30));

SELECT TAN(RADIANS(30));

SELECT ATAN(RADIANS(30));

SELECT ATAN2(1,RADIANS(30));

SELECT COT(RADIANS(30));

二、字符串函数

SELECT CHAR_LENGTH('fsf sfd');

SELECT CHAR_LENGTH('你');

SELECT LENGTH('你好fsfd');

SELECT LENGTH('你');

SELECT LENGTH('1');

SELECT ConCAT('423','你好fsfd');

SELECT CONCAT_WS('@','fdsf','25435');

SELECT INSERT('r3t3t',2,3,'rew');

SELECT UPPER('rewfdf');

SELECT UCASE('fdsfds');

SELECT LOWER('fdsfEREW');

SELECT LCASE('FSDREW');

SELECT LEFT('FDSFD',3);

SELECT RIGHT('fdsfds3342',4)

显示员工姓名的姓其他部分用*表示

SELECT LEFT(emp.emp_name,1)from emp;

SELECT CHARACTER_LENGTH(TRIM(emp.emp_name))-1 from emp;

SELECT REPLACE('*',LEFT(emp.emp_name,2),CHARACTER_LENGTH(TRIM(emp.emp_name))-1)from emp;

SELECT ConCAT(LEFT(emp.emp_name,1),REPLACE('*',LEFT(emp.emp_name,2),CHARACTER_LENGTH(TRIM(emp.emp_name))-1))from emp;

3.自定义函数