SQL 21 天自学通学习笔记 2

日期、时间函数：

select * from project;

针对日期型：

1. add_months: 增加月份

select * from task,startdate,enddate,original_end,add_months(enddate,2) from project;

select task tasks_shorter_than_one_month from project where add_months(startdate,1) > enddate;

2. last_day: 最后一天

select enddate,last_day (enddate) from project;

select distinct last_day('1-FEB-95') NON_LEAP,LAST_DAY('1-FEB-96') LEAP FROM PROJECT;

3. months_between: 中间有几个月

select task,startdate,enddate,months_between(enddate,startdate) duration from project;

select * from project where months_between('19 MAY 95',STARTDATE) > 0;

4. new_time: 调整时区

select enddate edt,new_time(enddate,'edt','pdt') from project;

5. next_day: 返回与指定日期同一星期或下一星期的，星期几的确切日期；

select startdate,next_day(startdate,'friday') from project;

6. sysdate:系统日期和时间

select distinct dysdate from project;

select * from project where startdate > sysdate;

数学函数：

1. ABS : 绝对值

select ABS(A) absolute_value from numbers;

2. CELL (比参数大的最小整数) 和 FLOOR(比参数小的最大整数)

select B，cell(B) ceiling from numbers;

select A，floor(A) floor from numbers;

3. COS COSH SIN SINH TAN TANH 三角函数，默认参数认定为弧度制；

4. EXP : 返回给定参数为指数，e为底数的幂值；

select A,EXP(A) from numbers;

5. LN : 返回给定参数的自然对数；

6. LOG: 返回结合参数的对数；

7. MOD: 取模；

SELECT A B MOD A B FROM NUMBERS

8. POWER: 幂数；

SELECT A B POWER A B FROM NUMBERS；

9. SIGN：如果参数的值为负数那么SIGN 返回-1 如果参数的值为正数那么SIGN 返回1

如果参数为零那么SIGN 也返回零；

SELECT A SIGN A FROM NUMBERS

10. SQRT：开方

SELECT A SQRT A FROM NUMBERS

字符串函数：

1. concat : 连接，等同“|| ”;

2. initcap：首字母转大写

select firstname before,initcap(firstname) after from characters;

3. upper,lower

select firstname,upper(firstname),lower(firstname) from characters

4. lpad,rpad 填充字符串，至少两个参数

SQL> select lastname,lpad(lastname,20,'*') from characters;

LASTNAME LPAD(LASTNAME,20,'*')

------------------------------------ ----------------------------------------

PURVIS **************PURVIS

TAYLOR **************TAYLOR

CHRISTINE ***********CHRISTINE

ADAMS ***************ADAMS

COSTALES ************COSTALES

KONG ****************KONG

6 rows selected

SQL> select lastname,rpad(lastname,20,'*') from characters;

LASTNAME RPAD(LASTNAME,20,'*')

------------------------------------ ----------------------------------------

PURVIS PURVIS**************

TAYLOR TAYLOR**************

CHRISTINE CHRISTINE***********

ADAMS ADAMS***************

COSTALES COSTALES************

5. ltrim,rtrim 截取字符串，至少一个参数

SQL> select lastname,rtrim(lastname) from characters;

LASTNAME RTRIM(LASTNAME)

------------------------------------ ------------------------------------

PURVIS PURVIS

TAYLOR TAYLOR

CHRISTINE CHRISTINE

ADAMS ADAMS

COSTALES COSTALES

KONG KONG

6 rows selected

6. replace : 替换

SQL> select lastname,replace(lastname,'ST','') replacement from characters;

LASTNAME REPLACEMENT

------------------------------------ ------------------------------------

PURVIS PURVIS

TAYLOR TAYLOR

CHRISTINE CHRIINE

ADAMS ADAMS

COSTALES COALES

KONG KONG

6 rows selected

SQL> select lastname,replace(lastname,'ST',null) replacement from characters;

LASTNAME REPLACEMENT

------------------------------------ ------------------------------------

PURVIS PURVIS

TAYLOR TAYLOR

CHRISTINE CHRIINE

ADAMS ADAMS

COSTALES COALES

KONG KONG

6 rows selected

SQL> select lastname,replace(lastname,'ST','*') replacement from characters;

LASTNAME REPLACEMENT

------------------------------------ ------------------------------------

PURVIS PURVIS

TAYLOR TAYLOR

CHRISTINE CHRI*INE

ADAMS ADAMS

COSTALES CO*ALES

KONG KONG

6 rows selected

7. substr ：截取字串

SQL> select firstname,substr(firstname,2,3) from characters;

FIRSTNAME SUBSTR(FIRSTNAME,2,3)

------------------------------------ ---------------------

kelly ell

CHUCK HUC

LAURA AUR

FESTER EST

ARMANDO RMA

MAJOR AJO

6 rows selected

SQL> select firstname,substr(firstname,3) from characters;

FIRSTNAME SUBSTR(FIRSTNAME,3)

------------------------------------ --------------------------------------------------------------------

kelly lly

CHUCK UCK

LAURA URA

FESTER STER

ARMANDO MANDO

MAJOR JOR

6 rows selected

8. translate : 翻译函数，三个参数，对大小写敏感

select firstname,translate(firstname,'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ','NNNNNNNNNNAAAAAAAAAAAAAAAAAAAAAAAAAA')

2 from characters;

FIRSTNAME TRANSLATE(FIRSTNAME,'012345678

------------------------------------ ------------------------------------------------------------------------

kelly kelly

CHUCK AAAAA

LAURA AAAAA

FESTER AAAAAA

ARMANDO AAAAAAA

MAJOR AAAAA

6 rows selected

9. instr 搜索函数

SQL> select lastname, instr(lastname,'O',2,1)from characters;

LASTNAME INSTR(LASTNAME,'O',2,1)

------------------------------------ -----------------------

PURVIS 0

TAYLOR 5

CHRISTINE 0

ADAMS 0

COSTALES 2

KONG 2

6 rows selected

10 lenght : 返回字符串的长度

SQL> select firstname,length(rtrim(firstname)) from characters;

FIRSTNAME LENGTH(RTRIM(FIRSTNAME))

------------------------------------ ------------------------

kelly 5

CHUCK 5

LAURA 5

FESTER 6

ARMANDO 7

MAJOR 5

6 rows selected

转换函数：

1. to_char: 转换成字符串；

select testnum,length(to_char(testnum)) from conversions;

TESTNUM LENGTH(TO_CHAR(TESTNUM))

------- ------------------------

95 2

23 2

68 2

2. to_number: 转换成数字；

select name,testnum,testnum*to_number(name) from conversions;

NAME TESTNUM TESTNUM*TO_NUMBER(NAME)

--------------- ------- -----------------------

40 95 3800

13 23 299

74 68 5032

3. greatest , least

SQL> select greatest('ALPHA','BRAVO','FOXTROT','DELTA') FROM CONVERSIONS;

GREATEST('ALPHA','BRAVO','FOXT

------------------------------

FOXTROT

SQL> select least(34,567,3,45,1090) from conversions;

LEAST(34,567,3,45,1090)

-----------------------

4. user 查询表所属的用户；

SQL> select user from characters;

USER

------------------------------

oracle

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