select abs (-100) from dual;--絕對值
select mod (8,5) from dual;--取模,取餘數
select ceil (12.1) from dual;--去上限值
select floor (12.1) from dual;--去下限值
select round (12.4567,3) from dual; -- 四捨五入
select trunc (12.456,2) from dual; -- 擷取，不四捨五入
select trunc (12.456,0) from dual; -- 擷取，不四捨五入(截整)
select length ('asddsa') from dual;--字串長度
select xingm, length (xingm) from t_hq_ryxx;
select xingm, substr (xingm,1,2) from t_hq_ryxx;--擷取，（從第一位開始擷取，截兩位）
select concat ('sa',concat ('sdsd','ddd')) from dual;
select 'sa'||'sdsd'||'ddd' from dual;
--查詢字串
select instr ('abcdef','d') from dual;
select instr ('abcdefdf','d',3) from dual;
select instr ('abcdefdf','d',5) from dual; --數字指定起始位置
select instr ('abcdefdf','dd',3) from dual; --找不到返回0
--轉換大小寫
select upper ('assa'),lower ('sdda') from dual;
select upper ('assa'),lower ('sdda'), initcap ('this is a car') from dual; --initcap 首字母轉換大寫
select replace ('abcdef','ab','123') from dual; --替換
update t_hq_ryxx set xingm = replace (xingm,'三','四') where xingm like '三%'
--填充
select rpad ('aa',8, 'c') from dual;
select rpad ('aba',8, 'de') from dual;
select lpad ('aa',8, 'rc') from dual;
--去空格
select trim (' wfat ') from dual; --去前後空格
select ltrim (' sd1 ') from dual; --去左空格
select rtrim (' sdad ') from dual; --去右空格
--去字首
select trim (leading 'a' from 'asda') from dual; --前邊開始
select trim (trailing 'a' from 'asda') from dual; --右邊開始
select trim (both 'a' from 'asda') from dual; --去前後
--日期型函式
select sysdate from dual;
select add_months(sysdate,2) from dual; --加兩個月
select add_months(sysdate,-2) from dual; --減兩個月
select last_day(sysdate) from dual;
select last_day(sysdate) +1 from dual; --（+）加天數
select last_day(sysdate) -1 from dual; --（-）減天數
--轉換函式
--select cast ('123' as number) from dual;
--select cast ('123' as number) + 123 from dual;
--select cast ('123' as varchar2(4)) from dual; --數字長度不能超過字串長度
--select cast(sysdate as varchar2(10)) from dual;
select to_char(sysdate, 'yyyy-mm-dd')from dual; --日期轉換字串(忽略大小寫)
select to_char(sysdate, 'yy-mm-dd')from dual;
select to_char(sysdate, 'yyyy-dd-mm hh24:mi:ss')from dual;
--select to_char(123.456,'9999.9')from dual;
select to_date('2015-12-11','yyyy-mm-dd') from dual; --字串轉換日期
select to_number('123.456','9999.999') from dual;
select( nianl + gongz) from t_hq_ryxx;
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