SQL Round Function

select * from simpledb.employee;

select avg(salary) from simpledb.employee;

select round(avg(salary), 2) from simpledb.employee;

마이너스로도 사용이 가능합니다.   당연히 반올림되죠

select round(avg(salary), -2) from simpledb.employee;

SQL Cast Function

Type이 BINARY, CHAR, DATE, DATETIME, TIME,DECIMAL, SIGNED, UNSIGNED

만 지원되네요. ( http://www.mysqltutorial.org/mysql-cast/ )

select cast(salary as signed ) from simpledb.employee;

select cast(salary as char(50) ) from simpledb.employee;

+ 대신에 concat를 사용하기 때문에 자동으로 숫자는 String으로 변경.

select concat(employee_name, salary) from simpledb.employee;

SQL Convert Function

Mysql 에서는 Cast()와 Convert() 같은것 같습니다.

SQL Concatenate

https://www.w3schools.com/sql/func_mysql_concat.asp

SQL Substring

https://www.w3schools.com/sql/func_mysql_substring.asp

시작은 1부터 0을 하면 첫글자 앞이네요

select substring(employee_name, 1, 3) from simpledb.employee;

SQL CharIndex - Instring

MySQL에서는 locate를 사용합니다. https://www.w3schools.com/sql/func_mysql_locate.asp

select locate('R', employee_name) from simpledb.employee;

SQL Trim, Rtrim, Ltrim

https://www.w3schools.com/sql/func_mysql_trim.asp

https://www.w3schools.com/sql/func_mysql_rtrim.asp

https://www.w3schools.com/sql/func_mysql_ltrim.asp

select '      hello       ';

select trim('      hello          ');

SQL Length

https://www.w3schools.com/sql/func_mysql_length.asp

len대신에 LENGTH