mysql learning function

* One-way function

* Length (number of bytes acquired)

select length("join")  返回4 

 

* Concat (mosaic)

select concat("firstname","_","last_name");   firstname_last_name

 

* Upper (All letters become uppercase)

select upper(zqc);   ZQC

 

* Lower (all lowercase letters changed)

select lower(ZQC);  zqc

 

* Substr (interception characters)

select substr("abcdef",3)    cdef

select substr("abcdef",2,3)  bcd 

 

* Instr (return substring starting index of the first occurrence, if not return 0)

select instr("abcdefg","cd")   3

select instr("abcdefg","cfd")   0

 

* Trim (remove the spaces before and after)

select  trim("    abc    ");      abc 

select trim("a" from "aaaaabbbbbaaaaaa")  bbbbb

 

* Lpad (left padding) 

select lpad("abc",10,"a")    aaaaaaaabc

select lpad("abc",2,"a")     ab

 

* Rpad (right padding)

select rpad ("abc",10,"a")  abcaaaaaaa

select rpad("abc",2,"a")    ab

   

* Replace (substitute)

select replace("abccdefg","abc","haha")    hahacdefg

select replace("abcdefgabcabc","abc","ha")    hadefghaha