第05章_单行函数

1.数值函数

基本的操作
SELECT ABS(-123),ABS(32),SIGN(-23),SIGN(43),PI(),CEIL(32.32),
CEILING(-43.23),FLOOR(32.32), FLOOR(-43.23),MOD(12,5) 
FROM DUAL;

取随机数
SELECT RAND(),RAND(),RAND(10),RAND(10),RAND(-1),RAND(-1) 
FROM DUAL;

四舍五入，截断操作
SELECT ROUND(123.556),ROUND(123.456,0),ROUND(123.456,1),
ROUND(123.456,-1),ROUND(153.456,-2)
FROM DUAL;

SELECT TRUNCATE(123.456,0),TRUNCATE(123.456,1),TRUNCATE(129.456,-1)
FROM DUAL;

单行函数可以嵌套

SELECT TRUNCATE(ROUND(123.456,2),0)
FROM DUAL;

角度与弧度的互换

SELECT RADIANS(30),RADIANS(45),RADIANS(60),RADIANS(90),
DEGREES(2 * PI()),DEGREES(RADIANS(60))
FROM DUAL;

三角函数

SELECT SIN(RADIANS(30)),DEGREES(ASIN(1)),TAN(RADIANS(45)),
DEGREES(ATAN(1))
FROM DUAL;

指数和对数

SELECT POW(2,5),POWER(2,4),EXP(2)
FROM DUAL;

SELECT LN(EXP(2)),LOG(EXP(2)),LOG10(10),LOG2(4)
FROM DUAL;

进制间的的转换

SELECT BIN(10),HEX(10),OCT(10),CONV(10,2,8)
FROM DUAL;

2.字符串函数

SELECT ASCII('Abcdefsf'),CHAR_LENGTH('hello'),CHAR_LENGTH('我们'),
LENGTH('hello'),LENGTH('我们')
FROM DUAL;


 xxx worked for yyy
SELECT CONCAT(emp.last_name,' worked for ',mgr.last_name) "details"
FROM employees emp JOIN employees mgr
WHERE emp.manager_id = mgr.employee_id;


SELECT CONCAT_WS('_','hello','world','hello','beijing')
FROM DUAL;

字符串的索引是从1开始的！

SELECT INSER