What is the main difference between a UNION statement and a UNION ALL statement? 1. A UNION statement eliminates duplicate rows; a UNION ALL statement includes duplicate rows. 2. A UNION statement can be used to combine any number of queries; a UNION ALL statement can be used to combine a maximum of two queries. 3. A UNION statement can only combine queries that have parallel fields in the SELECT list; a UNION ALL statement can combine queries with differing SELECT list structures. 4. A UNION statement cannot be used with aggregate functions; a UNION ALL statement can be used with aggregate functions. 5. There is no difference between the two statements; they are interchangeable.

2 Answers   Saman Bank, Sonata,

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Can a procedure in a package be overloaded?

0 Answers   EXL,

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how to check the 3rd max salary from an employee table? One of the queries used is as follows: select sal from emp a where 3=(select count(distinct(sal)) from emp b where a.sal<=b.sal). Here in the sub query "select count(distinct(sal)) from emp b where a.sal<=b.sal" or "select count(distinct(sal)) from emp b where a.sal=b.sal" should reveal the same number of rows is in't it? Can any one here please explain me how is this query working perfectly. However, there is another query to get the 3rd highest of salaries of employees that logic I can understand. Pls find the query below. "select min(salary) from emp where salary in(select distinct top 3 salary from emp order by salary desc)" Please explain me how "select sal from emp a where 3=(select count(distinct(sal)) from emp b where a.sal<=b.sal)" works source:http://www.allinterview.com/showanswers/33264.html. Thanks in advance Regards, Karthik.

4 Answers  

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State some properties of relational databases?

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