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what is the difference between trigger and constraint?
 Question Submitted By :: SQL-PLSQL
I also faced this Question!!     Answer Posted By  
# 1
Constraints implements specific conduct or rules on table column like it determines whether field data should be unique,not null ..
But triiger implements rules on systems or application event.
whenever dml occurs that implemented rules been fired.
Is This Answer Correct ?    3 Yes 0 No
Kumar Jabu
# 2
Triggers not apply for existing rows but constraints can
apply for existing rows.
Is This Answer Correct ?    1 Yes 0 No
Naga Sindhuri

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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: Thanks in advance Regards, Karthik.   4
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