select lower('HelloWorld');
select upper('HelloWorld');
select concat(name,'的月薪是:',sal) from dual;
select char_length('我今年23歲') from dual;
select length('我今年23歲') from dual;
一個英文字母,數字佔一個字節,一箇中文佔三個字節函數
select lpad('ABC',7,'X'),lpad('ABC',3,'X'),lpad('ABC',1,'X') from dual;
select rpad('ABC',7,'X'),rpad('ABC',3,'X'),rpad('ABC',1,'X') from dual;
select ltrim(' A B C '),rtrim(' A B C '),trim(' A B C ') from dual;
select substring('ABCDEFGHI',3),substring('ABCDEFGHI',3,3) from dual;spa
select abs(-32);
select mod(42,10); select 42 mod 10;
select pi();
select pow(2,4);
select ceil(0.5),ceil(-1.5),ceil(1.5);
select floor(0.5),floor(-1.5),floor(1.5);
select round(-1.49),round(-1.50),round(1.49),round(1.50);
select round(-123.456789,3),round(-123.456789,3);/*小數點第n位,n位四捨五入*/
select round(-123.456789,3),round(-123.456789,-3); /*小數點前用負號*/
select now();
select date_add('2019-04-06',interval 100 day); /*也能夠-100*/ select date_add(now(),interval 100 day);
select date_sub('2019-04-06',interval 100 day); select date_sub(now(),interval 100 day);
select current_date();
select current_time();
select datediff('2015-12-31','2016-12-31');
select year(now()),month(now()),minute(now());
select unix_timestamp(now());
select from_unixtime(unix_timestamp(now()));
select format(123456.789,2);/*保留D位小數*/
select date_format(now(),'%Y-%m-%d');
select str_to_date('2018,05,20','%Y,%m,%d');