很久以前看某本书整理的，忘了哪本了，现在贡献出来。

1)在select语句中使用条件逻辑

1

select ename,sal,2casewhen sal<=2000then 'UNDERPAID'3            when sal>=4000then 'OVERPAID'4else'OK'5       end as status6from emp

ENAME SAL STATUS

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

SMITH 800 UNDERPAID

ALLEN 1600 UNDERPAID

WARD 1250 UNDERPAID

JONES 2975 OK

MARTIN 1250 UNDERPAID

BLAKE 2850 OK

CLARK 2450 OK

SCOTT 3000 OK

KING 5000 OVERPAID

TURNER 1500 UNDERPAID

ADAMS 1100 UNDERPAID

JAMES 950 UNDERPAID

FORD 3000 OK

MILLER 1300 UNDERPAID

2)从表中随机返回n条记录

1

select*2  from (3    select ename, job4    from emp5    order by dbms_random.value()6  )7  where rownum<=5

3)按照子串排序

比如要从EMP表中返回员工名字和职位，并且按照职位字段最后2个字符排序

1

select ename,job2  from emp3order by substr(job,length(job)-2)

ENAME JOB

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

KING PRESIDENT

SMITH CLERK

ADAMS CLERK

JAMES CLERK

MILLER CLERK

JONES MANAGER

CLARK MANAGER

BLAKE MANAGER

ALLEN SALESMAN

MARTIN SALESMAN

WARD SALESMAN

TURNER SALESMAN

SCOTT ANALYST

FORD ANALYST

4)处理空值排序

当被排序的列存在空值，如果希望空值不影响现有排序

1

select ename,sal,comm2   from emp3order by comm nulls last

ENAME SAL COMM

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

TURNER 1500 0

ALLEN 1600 300

WARD 1250 500

MARTIN 1250 1400

SMITH 800

JONES 2975

JAMES 950

MILLER 1300

FORD 3000

ADAMS 1100

BLAKE 2850

CLARK 2450

SCOTT 3000

KING 5000

1

select ename,sal,comm2  from emp3order by comm desc nulls first

ENAME SAL COMM

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

SMITH 800

JONES 2975

CLARK 2450

BLAKE 2850

SCOTT 3000

KING 5000

JAMES 950

MILLER 1300

FORD 3000

ADAMS 1100

MARTIN 1250 1400

WARD 1250 500

ALLEN 1600 300

TURNER 1500 0

5)根据数据项的键排序

比如如果job是“SALESMAN”，根据COMM排序，否则根据SAL排序

1

select ename,sal,job,comm2  from emp3 order bycasewhen job='SALESMAN' then commelsesal end

ENAME SAL JOB COMM

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

TURNER 1500 SALESMAN 0

ALLEN 1600 SALESMAN 300

WARD 1250 SALESMAN 500

SMITH 800 CLERK

JAMES 950 CLERK

ADAMS 1100 CLERK

MARTIN 1250 SALESMAN 1300

MILLER 1300 CLERK

CLARK 2450 MANAGER

BLAKE 2850 MANAGER

JONES 2975 MANAGER

SCOTT 3000 ANALYST

FORD 3000 ANALYST

6)从一个表中查找另一个表中没有的值

比如要从DEPT中查找在表EMP中不存在数据的所有部门(数据中，DEPTNO值为40的记录在表EMP中不存在)

1

select deptno from dept2minus3select deptno from emp

7)在运算和比较时使用null值

null不会等于和不等于任何值，null和自己都不等于。以下例子是当comm有null的情况下列出比“WARD”提成低的员工。 (coalesce函数将null转换为其他值)

1

select ename,comm,coalesce(comm,0)2  from emp3where coalesce(comm,0)                                     from emp5                                    where ename='WARD' )

ENAME COMM COALESCE(COMM,0)

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

SMITH 0

ALLEN 300 300

JONES 0

BLAKE 0

CLARK 0

SCOTT 0

KING 0

TURNER 0 0

ADAMS 0

JAMES 0

FORD 0

MILLER 0

8)删除重复记录

对于名字重复的记录，保留一个

1

deletefrom dupes2 where id notin( select min(id)3                      from dupes4                     group by name )

9)合并记录

比如如下需求：

如果表EMP_COMMISSION中的某员工也存在于EMP表，那么更新comm为1000

如果以上员工已经更新到1000的员工，如果他们SAL少于2000，删除他们

否则，从表中提取该员工插入表EMP_COMMISSION

1

merge into emp_commission ec2using (select*from emp) emp3    on (ec.empno=emp.empno)4 when matched then5       update set ec.comm=10006deletewhere (sal<2000)7 when not matched then8        insert (ec.empno,ec.ename,ec.deptno,ec.comm)9       values (emp.empno,emp.ename,emp.deptno,emp.comm)

10)用sql生成sql

1

select 'select count(*) from '||table_name||';' cnts2  from user_tables;

(user_tables是oracle的元数据表之一)

CNTS

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

select count(*) from ANT;

select count(*) from BONUS;

select count(*) from DEMO1;

select count(*) from DEMO2;

select count(*) from DEPT;

select count(*) from DUMMY;

select count(*) from EMP;

select count(*) from EMP_SALES;

select count(*) from EMP_SCORE;

select count(*) from PROFESSOR;

select count(*) from T;

select count(*) from T1;

select count(*) from T2;

select count(*) from T3;

select count(*) from TEACH;

select count(*) from TEST;

select count(*) from TRX_LOG;

select count(*) from X;

11)计算字符在字符串里的出现次数

判断字符串里有多少个‘ , ’

1

select (length('10,CLARK,MANAGER')-2  length(replace('10,CLARK,MANAGER',',','')))/length(',')3  as cnt4from t1

先计算原字符串长度，再减去去掉逗号的长度，这个差再除以‘，’的长度

12)将数字和字母分离

原数据是：

DATA

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

SMITH800

ALLEN1600

WARD1250

JONES2975

MARTIN1250

BLAKE2850

CLARK2450

SCOTT3000

KING5000

TURNER1500

ADAMS1100

JAMES950

FORD3000

MILLER1300

1

select replace(2  translate(data,'0123456789','0000000000'),'0') ename,3  to_number(4    replace(5    translate(lower(data),6      'abcdefghijklmnopqrstuvwxyz',7      rpad('z',26,'z')),'z')) sal8  from (9    select ename||sal data from emp10 )

ENAME SAL

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

SMITH 800

ALLEN 1600

WARD 1250

JONES 2975

MARTIN 1250

BLAKE 2850

CLARK 2450

SCOTT 3000

KING 5000

TURNER 1500

ADAMS 1100

JAMES 950

FORD 3000

MILLER 1300

思路是很复杂的，比如先去除数字，是先把所有数字翻译为0，然后用replace去掉0.

13)根据表中的行创建分割列表

表中数据：

DEPTNO EMPS

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

10 CLARK

10 KING

10 MILLER

20 SMITH

20 ADAMS

20 FORD

20 SCOTT

20 JONES

30 ALLEN

30 BLAKE

30 MARTIN

30 JAMES

30 TURNER

30 WARD

1

select deptno,2    ltrim(sys_connect_by_path(ename,','),',') emps3  from (4  select deptno,5    ename,6    row_number() over7       (partition by deptno order by empno) rn,8    count(*) over9      (partition by deptno) cnt10  from emp11  )12  where level=cnt13  startwithrn=114    connect by prior deptno=deptno and prior rn=rn-1

查询结果

DEPTNO EMPS

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

10 CLARK,KING,MILLER

20 SMITH,JONES,SCOTT,ADAMS,FORD

30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES

14)按字母顺序排序

1

select old_name, new_name2  from (select old_name, replace(sys_connect_by_path(c, ' '), ' ') new_name3          from (select e.ename old_name,4                       row_number() over(partition by e.ename order by substr(e.ename, iter.pos,1)) rn,5                       substr(e.ename, iter.pos,1) c6                  from emp e, (select rownum pos from emp) iter7                 where iter.pos<=length(e.ename)8                 order by1) x9         startwithrn=110        connect by prior rn=rn-111               and prior old_name=old_name)12 where length(old_name)=length(new_name)

You would like the result to be:

OLD_NAME NEW_NAME

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

ADAMS AADMS

ALLEN AELLN

BLAKE ABEKL

CLARK ACKLR

FORD DFOR

JAMES AEJMS

JONES EJNOS

KING GIKN

MARTIN AIMNRT

MILLER EILLMR

SCOTT COSTT

SMITH HIMST

TURNER ENRRTU

WARD ADRW