Common Functions
① Function: The method is similar to Java, a language is encapsulated in a set of logical method body, the external exposure method name.
. ② benefits: hide implementation details; 2 improves the reusability of the code;.
③ call: select function name (argument list) table [from]
④ Category: 1. one-way function, such as concat, length, ifnull the like;
2. The packet function; do use statistics, also known as statistical functions, aggregate functions, function group;
A character function
① length byte parameter acquired;
SELECT length ( ' John ' ); # 4 results
SELECT length ( ' Chi Master ' ); # result. 9; the UTF8 one letter occupies one byte, a character occupies . 3 bytes
② concat string concatenation
select concat(last_name, '_', first_name) 姓名 from employees;
③ upper，lower
SELECT Upper ( ' Jhon ' ); variant # uppercase letters SELECT Lower ( ' JHON ' ); # letters to lower case
Example ② and ③ in combination:
the SELECT concat (Upper (last_name), Lower (first_name) name from the Employees; # change the name in uppercase, lowercase name change, then splicing
④ substr / substring; interception of characters, there are two usage
Use a:
SELECT substr ( ' Limo Chou Lu Chin element in love ' , 7 ); # Results are shown as 'Fair Lu Yuan'; This usage represents all the characters taken from the back of the specified index;
Usage of Two:
SELECT substr ( ' Limo Chou Lu Chin element in love ' , 1 , 3 ); # Results are shown as 'Limo Chou'; represents a character from the character length intercepts this usage index
Example: Name the first character in uppercase, lowercase other characters, and then use _ stitching, displayed
select concat(upper(substr(last_name,1,1)), '_', lower(substr(last_name,2))) out_put from employees;
⑤ instr substring sequence number returns the index of the first occurrence, returns 0 if no
Example:
SELECT InStr ( ' Yang Buhui love with six Yin Xia ' , ' Yin six Man ' ) AS out_put; results are shown as # 7;
⑥ trim function
trim () remove spaces on either side of the string;
SELECT TRIM ( ' Cuishan ' ) AS out_put; # Results are shown as 'Cuishan';
TRIM ( 'character 1', from 'string 2') , respectively, deletes a specified character string 1 from both sides ;
Example:
SELECT TRIM ( ' A ' , from ' AAAA sheets aaa Greenfield AAAA ' ) AS out_put; # Results are shown as 'aaa Greenfield sheets';
⑦ LPAD achieve left filled with the specified character specified length;
SELECT LPAD ( ' Yin Susu ' , 10 , ' * ' ) the AS out_put; # Results are shown as "******* Yin Susu '
⑧ RPAD achieve the right filled with the specified character specified length;
SELECT RPAD ( ' Yin Susu ' , 12 is , ' ab & ' ) out_put the AS; results are shown as 'Yin Susu ababababa'
⑨ replace replace
SELECT Replace ( ' zhangwuji Zhou Zhiruo in love ' , ' Zhou Zhiruo ' , ' Zhao ' ) out_put the AS; # result is 'love with Zhao zhangwuji'