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How to check the performance of SQL queries.

Posted By :Ashutosh Jha     Posted Date :August 31, 2014    Points :40   Category :Sql Server 
Sql Queries performance can be checked by using the Query optimization. we can check the query execution plan that how much time the query is taking to execute and then we can find-out that which part of the query is taking more time. The issue could e incorrect joins which is leading for more time to get the results. or in-proper sub-queries. By query execution plan, we can track the execution of the queries and then optimize it if required.

You can also find related Interview Question to How to check the performance of SQL queries.  below: 

How can we check that some changes have been made to dataset since it was loaded?


The changes made to the dataset can be tracked using the GetChanges and HasChanges methods.
The GetChanges returns dataset which are changed since it was loaded or since Acceptchanges was executed.

The HasChanges property indicates if any changes were made to the dataset since it was loaded or if acceptchanges method was executed.

The RejectChanges can be used to revert thee changes made to the dataset since it was loaded


What is Check Constraint?

Check constraint specifies a condition that is enforced for each row of the table on which the constraint is defined. Once constraint is defined, insert or update to the data within the tables is checked against the defined constraint

What is the difference between RULE and Check Constraint?

The major difference between rule and Check is reusability. Check constraint is associated with columns in a Table. So these can't be re-used. Rules are defined with in a database and can be applied to any number of columns. (More...)

What are the factors that affect the performance of NIC?

The following factors affect the performance of NIC,

Bus Speed :- It depends on ISA or PCI slot. PCI has higher speed.

Memory :- More the memory, better the performance.

Memory Access Method :- DMA is faster than I/O method. (More...)

ATM - Performance ?

1. Throughput - Rate at which ATM cells depart from the ATM switch.

2.Connection Blocking Probability - Defines the probability of Non-availability of enough resources for generating physical
connections between inlet and outlet .

3. Cell Loss Probability - Defines a no. of data cell that can be handled by a switch queue.

4. Switching Delay - Time required for cell to pass through the ATM switch.

5. Cell Delay Variation - Probability that the switching delay of the ATM switch exceeds the certain value . (More...)

How do you improve the performance of a server?

First check the processor and memory usage to see that processor is not above 80% utilization and memory not above 40-45% utilization then check the disk utilization using Performance Monitor, Secondly, use SQL Profiler to check for the users and current SQL activities and jobs running which might be a problem. Third would be to run UPDATE_STATISTICS command to update the indexes (More...)

Performance wise which one is the best? IN,EXISTS or INNER JOIN

It depends.

Generally speaking JOINs are much better than EXISTS & EXISTS is better than IN, performance wise.

If your result set is small then you can use IN or EXISTS.

But if result set contains a large set of records, then use JOINS.


How can check the Oracle version information from the command prompt?

Version information is stored in a table called v$version. In this table we can find version information on Oracle, PL/SQL, etc.

To retrieve the version information for Oracle, we can execute the following SQL statement:

select * from v$version
where banner like 'Oracle%'; (More...)

What are check constraint

? A CHECK constraint is used to limit the values that can be placed in a column.
? The check constraints are used to enforce domain integrity.

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