Mysql 函数学习

SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL

-> 0,0,1    

SELECT IF(0.1,1,0)

->0

SELECT IF(0.1<>0,1,0)

->1

SELECT CONCAT_WS(',','First name','Second name','Last Name');

->'Firstname,Second name,Last Name'

SELECT ELT(1,'ej','Heja','hej','foo');

->'ej'

SELECT FIELD('ej','Hej','ej','Heja','hej','foo');

->2

SELECT FIND_IN_SET('b','a,b,c,d');

->2

INSERT(str,pos,len,newstr)返回字符串str，其子字符串起始于pos位置和长期被字符串newstr取代的len字符

SELECT INSERT('Quadratic',3,4,'What');

->'QuWhattic'

INSTR(str,substr)返回字符串的第一个出现位置

SELECT INSTR('foobarbar','bar');

->4

LEFT(str,len)返回从字符串str开始的len最左字符

SELECT LEFT('foobarbar',5);

->'fooba'

LOCATE(substr,str),LOCATE(substr,str,pos)

LPAD(str,len,padstr)返回字符串str，其左边由字符串padstr填补len字符长度，假如str长度大于len，则返回值缩短至len字符

SELECT LPAD('hi',4,'??')

->'??hi'

SELECT LPAD('hi',1,'??')

->'h'

SELECT TRIM('   bar   ');

->'bar'

SELECT TRIM(LEADING 'x' FROM 'xxxbarxxx')

->'barxxx'

SELECT TRIM(BOTH 'x' FROM 'xxxbarxxx')

->'bar'

SELECT TRIM(TRAILING 'xyz' FROM 'barxxyz')

->'barx'

SELECT MAKEDATE(2009,31),MAKEDATE(2009,32);

->'2009-01-31','2009-02-01';

SELECT STR_TO_DATE('04/31/2009','%m/%d/%Y');

->'2009-04-31'