ORACLE循序渐进讲解（第三讲）

SQL> select to_date('2014-10-11 12:13:14','yyyy-mm-dd hh:mi:ss') from dual;
TO_DATE('2014-10-1112:13:14','
------------------------------
2014-10-11 12:13:14

SQL> select trunc(sysdate,'month') from dual;
TRUNC(SYSDATE,'MONTH')
----------------------
2014-11-01

SQL> select trunc(last_day(sysdate)) from dual;
TRUNC(LAST_DAY(SYSDATE))
------------------------
2014-11-30

SQL> select trunc(sysdate,'year') from dual;
TRUNC(SYSDATE,'YEAR')
---------------------
2014-01-01

SQL> select add_months(trunc(sysdate,'year'),12)-1 from dual;
ADD_MONTHS(TRUNC(SYSDATE,'YEAR
------------------------------
2014-12-31

SQL> select cast(to_char(last_day(sysdate),'dd') as int) from dual;
         CAST(TO_CHAR(LAST_DAY(SYSDATE)
---------------------------------------
                                     30

SQL> select last_day(sysdate)-sysdate from dual;
LAST_DAY(SYSDATE)-SYSDATE
-------------------------
                        8

SQL> select next_day(sysdate,1) from dual;
NEXT_DAY(SYSDATE,1)
-------------------
2014-11-23 17:39:48

<pre name="code" class="sql" style="font-size: 14px;">SQL> <span style="font-family: Arial, Helvetica, sans-serif;">select months_between(to_date('2014-11-01','yyyy-mm-dd'),to_date('2014-01-01','yyyy-mm-dd')) from dual;</span>

SQL> select to_char(sysdate,'yyyy-mm') from dual;
TO_CHAR(SYSDATE,'YYYY-MM')
--------------------------
2014-11

SQL> select upper('a') || lower('B') || length('aaa') from dual;
UPPER('A')||LOWER('B')||LENGTH
------------------------------
Ab3

SQL> select lpad('aaa',5,'*'),rpad('aaa',5,'*') from dual;
LPAD('AAA',5,'*') RPAD('AAA',5,'*')
----------------- -----------------
**aaa             aaa**

SQL> select ltrim('abbb','a'),rtrim('1234','4'),trim(' ABC ') from dual;
LTRIM('ABBB','A') RTRIM('1234','4') TRIM('ABC')
----------------- ----------------- -----------
bbb               123               ABC

SQL> select substr('abcde',1,2) from dual;
SUBSTR('ABCDE',1,2)
-------------------
ab

SQL> select instr('abcad','a',1),instr('abcad','a',2,1) from dual;
INSTR('ABCAD','A',1) INSTR('ABCAD','A',2,1)
-------------------- ----------------------
                   1                      4

SQL> select round(12.12),round(12.12,1),round(12.12,-1) from dual;
ROUND(12.12) ROUND(12.12,1) ROUND(12.12,-1)
------------ -------------- ---------------
          12           12.1              10

SQL> select trunc(12.12),trunc(12.12,1),trunc(12.12,-1) from dual;
TRUNC(12.12) TRUNC(12.12,1) TRUNC(12.12,-1)
------------ -------------- ---------------
          12           12.1              10

SQL> select mod(1,3),ceil(12.56),floor(12.56) from dual;
  MOD(1,3) CEIL(12.56) FLOOR(12.56)
---------- ----------- ------------
         1          13           12

SQL> select sys_context('userenv','db_name') dbName,sys_context('userenv','nls_date_format') date_fromat from dual;
DBNAME                                                                           DATE_FROMAT
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