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SQL: Subqueries

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zahiruddin said…
Hi sir this is zahiruddin from QSPIDER,i have interview on saturday but am not getting the answer with these questions can u tel me the answer ...
1. Two tables emp (empid, name, deptid, sal) and dept(deptid, deptname) are there. Write a query which displays empname, corresponding deptname also display those employee names who do not belong to any dept.

2. Display the employees whose salary is less than average salary.

this is my mail id please froward it sir..
sayzaheer@gmail.com
Mithun Ashok said…
Hi Zahiruddin,

1. SELECT e.ename, e.deptno, d.dname
FROM emp e, dept d
WHERE e.deptno (+) = d.deptno;

2. select * from emp where sal < (select avg(sal) from emp);

Have also sent this to your mail id.

Regards,
Mithun
baba said…
hello mithun u r a good looking and i want this answer can u explain plz explain how this query works
pradeep said…
can u plz explain how this query works

select a.sal from emp a
where 0=(select count(*) from emp b
where b.sal>a.sal)
/
Mithun Ashok said…
Hi Pradeep,

This is a co-related sub query. Please go through my presentation on Subqueries below.

SUBQUERIES

Regards,
Mithun
Anonymous said…
can u tel me how this query works

SELECT REPLACE(TRANSLATE(LTRIM(RTRIM('!! ATHEN !!','!'), '!'), 'AN', '**'),'*','TROUBLE') FROM DUAL;

we get this answer plz tel sir
TROUBLETHETROUBLE
Mithun Ashok said…
Hi Anonymous,

Always innermost function gets executed first,

check below,

SQL> select RTRIM('!! ATHEN !!','!') from dual;

RTRIM('!!
---------
!! ATHEN


You are first doing RTRIM and removing all ! from right side.

Next,

SQL> select LTRIM('!! ATHEN','!') from dual;

LTRIM(
------
ATHEN

You have used LTRIM to remove ! from left.

SQL> select TRANSLATE(' ATHEN', 'AN','**') from dual;

TRANSL
------
*THE*


Now you are using TRANSLATE function to replace A with * and N with *.

SQL> select REPLACE(' *THE*','*','TROUBLE') from dual;

REPLACE('*THE*','*
------------------
TROUBLETHETROUBLE

Finally you are replacing * with TROUBLE.


Hope this is clear.

Regards,
Mithun
Ravi Verma said…
Hello sir,
this is ravi here.
Would you please explain the following questions...
1>What is the advantage of JOINS over correlations??
2>Give some specific condition
when we should use joins and
when we should use correlation??
Pramodnkul90 said…
sir when we go for subqueries?i mean can u explain me wit 1 scenario?pls
veda said…
Two tables emp(empid,name,deptid,sal) and dept(deptid,deptname) are there.write a query which displays empname,corresponding deptname also display those employee names who donot belong to any dept.
Unknown said…
hai sir,how to display second row in the table??

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