Comments on: SQL SERVER – Performance Comparison – INSERT TOP (N) INTO Table – Using Top with INSERT

By: SQL SERVER – Weekly Series – Memory Lane – #019 | SQL Server Journey with SQL Authority

Sat, 09 Mar 2013 01:31:43 +0000

[...] Performance Comparison – INSERT TOP (N) INTO Table – Using Top with INSERT This has been one of the most fun blog posts ever. Initially I had no clue that TOP (N) even works with INSERT but later I learned the same and found it very interesting. In this blog post I have compared the performance between TOP N with INSERT and INSERT with SELECT N. [...]

By: SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 13 of 31 Journey to SQLAuthority

Wed, 13 Jul 2011 01:30:53 +0000

[...] INSERT TOP (N) INTO Table is faster than Using Top with INSERT but when we use INSERT TOP (N) INTO Table, the ORDER BY clause is totally ignored. (Read more here) [...]

By: Mohammed Mubarak

Mohammed Mubarak — Mon, 14 Feb 2011 12:53:33 +0000

Hi,

I want clear picture of Execution Plan. plz do the needful.

Regards,
Mubarak

By: Krishna

Krishna — Fri, 09 Jul 2010 10:15:28 +0000

/* Preserve the Order by enclosing SELECT code in EXEC without effecting performance. Query cost is for Option1 is 65% and for Option2 is 35% */

– Option 1: Top with Select
INSERT INTO InsertTestValue (ID)
SELECT TOP (2) ID
FROM TestValue
ORDER BY ID DESC;
GO

– Option 2: Top with Insert
INSERT TOP (2) INTO InsertTestValue1 (ID)
EXEC (‘SELECT ID
FROM TestValue
ORDER BY ID DESC’);

By: Madhivanan

Madhivanan — Thu, 04 Mar 2010 11:20:28 +0000

Yes. It has the same effect for temp tables and table variables

By: Madhivanan

Madhivanan — Thu, 04 Mar 2010 11:17:20 +0000

This is the expected behaviour

As per BOL

TOP ( expression ) [ PERCENT ]
Specifies the number or percent of random rows that will be inserted. expression can be either a number or a percent of the rows. The rows referenced in the TOP expression that are used with INSERT, UPDATE, or DELETE are not arranged in any order.

By: Sushil

Sushil — Wed, 03 Mar 2010 17:26:29 +0000

It is understood how the SQL Server deals with Insert Top (N) into..Select …. and Insert into…Select Top (N) and their performance as well… I dont think comparison here is needed since the results are different.

I wanted to know why in the backgroud SQL Server is unable to Order By when Top is issued with Insert. I would really appreciate if you could clarify. Thanks much.

By: Ramdas

Ramdas — Wed, 03 Mar 2010 14:16:41 +0000

Interesting to see how the results are diferent with the diferent placement of the TOP clause. Thanks for the examples.

By: Zuberkhan

Zuberkhan — Wed, 03 Mar 2010 08:29:34 +0000

Performance of 2nd query is better because SORT operation is not used to retrieve the records (pls see the execution plan). Both of these queries performance should be evaluated by removing order by clause.

By: pinaldave

pinaldave — Wed, 03 Mar 2010 07:37:10 +0000

Table variable OR Temp tables are totally different things. We will talk some other time on them.

Kind Regards,
Pinal

By: Tejas Shah

Tejas Shah — Wed, 03 Mar 2010 06:52:34 +0000

Excellent comparison.

Need to check this in detail…you give a new way to consider this thing too.

One question in my mind is:

Is it same for Table variable OR Temp tables?

Tejas
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