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what is the difference between where clause and having clause
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WHERE clause is used to impose condition on SELECT
statement as well as single row function and is used before
GROUP BY clause where as HAVING clause is used to impose
condition on GROUP Function and is used after GROUP BY
clause in the query
WHERE applies to rows HAVING applies to summarized rows
(summarized with GROUP BY) if you wanted to find the
average salary in each department GREATER than 333 you
would code:
SELECT DEPARTMENT AVG(SALARY)
FROM EMP
WHERE DEPARTMENT > 333
GROUP BY DEPARTMENT
IF you then wanted to filter the intermediate result to
contain departments where the average salary was greater
that 50 000 you would code:
SELECT DEPARTMENT AVG(SALARY)
FROM EMP
WHERE DEPARTMENT > 333
GROUP BY DEPARTMENT
HAVING AVG(SALARY) > 50000.
Where executes first
GROUP BY next
and finally HAVING
| Is This Answer Correct ? | 9 Yes | 0 No |
Answer / selvam a
HAVING clause can only compare a built in function but WHERE
clause can compare column name.
| Is This Answer Correct ? | 0 Yes | 0 No |
If I have a view which is a join of two or more tables, can this view be updatable?
in my table i will update only 100 record among 1000 records i need to display recently updated record'.....can u tell me where those records are stored how can i display those records...?if there is any sql query pls let me know....?
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SET is the ANSI standard for variable assignment, SELECT is not. SET can only assign one variable at a time, SELECT can make multiple assignments at once. If assigning from a query, SET can only assign a scalar value. If the query returns multiple values/rows then SET will raise an error. SELECT will assign one of the values to the variable and hide the fact that multiple values were returned (so you'd likely never know why something was going wrong elsewhere - have fun troubleshooting that one) When assigning from a query if there is no value returned then SET will assign NULL, where SELECT will not make the assignment at all (so the variable will not be changed from it's previous value) As far as speed differences - there are no direct differences between SET and SELECT. However SELECT's ability to make multiple assignments in one shot does give it a slight speed advantage over SET.
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