June 28, 2012 at 3:38 am
I’m trying to insert data from 1 table to another in a specific order.
Lets say in table1, I have data saying 4,2,3,1
Now I need to insert data from table1 to table2 in a specific order say 1,2,3,4
So I’m writing query: insert table2(id) select id from table1 order by id.
I’m assuming data should go like 1,2,3,4 but its not the case always. Everytime it goes in different order say 1,3,2,4 or 1,2,3,4 or 4,3,2,1 or 1,3,4,2
Could you please suggest on that,
June 28, 2012 at 4:40 am
Hi
SQL does not store data as an ordered set, there is no way to guarantee the order of an INSERT even using an ORDER BY
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June 28, 2012 at 5:36 am
Doesn't make much sense what you're trying to do here.
If you want to display your data in a specific order just use order by in yor select. As simple as that.
Or create a clustered index on your destination table.
June 28, 2012 at 5:41 am
Mahesh Gupta-325917 (6/28/2012)
I’m trying to insert data from 1 table to another in a specific order.Lets say in table1, I have data saying 4,2,3,1
Now I need to insert data from table1 to table2 in a specific order say 1,2,3,4
So I’m writing query: insert table2(id) select id from table1 order by id.
I’m assuming data should go like 1,2,3,4 but its not the case always. Everytime it goes in different order say 1,3,2,4 or 1,2,3,4 or 4,3,2,1 or 1,3,4,2
Could you please suggest on that,
Create a Clustered Index in table2 on column id
--rhythmk
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June 28, 2012 at 7:43 am
rhythmk (6/28/2012)
Mahesh Gupta-325917 (6/28/2012)
I’m trying to insert data from 1 table to another in a specific order.Lets say in table1, I have data saying 4,2,3,1
Now I need to insert data from table1 to table2 in a specific order say 1,2,3,4
So I’m writing query: insert table2(id) select id from table1 order by id.
I’m assuming data should go like 1,2,3,4 but its not the case always. Everytime it goes in different order say 1,3,2,4 or 1,2,3,4 or 4,3,2,1 or 1,3,4,2
Could you please suggest on that,
Create a Clustered Index in table2 on column id
Be careful here. If I read what it sounds like you are saying, you are suggesting to create this clustered index so the rows in table2 will be "ordered" correctly? There are times when you really do want an order by for an insert (if there is an identity on the target). However sql will still store this data in what it finds the most convenient. If you want your data from table2 to be returned in a certain order there is 1 and only 1 way to achieve this...use an order by when you pull the data out.
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June 29, 2012 at 12:05 am
Sean Lange (6/28/2012)
rhythmk (6/28/2012)
Mahesh Gupta-325917 (6/28/2012)
I’m trying to insert data from 1 table to another in a specific order.Lets say in table1, I have data saying 4,2,3,1
Now I need to insert data from table1 to table2 in a specific order say 1,2,3,4
So I’m writing query: insert table2(id) select id from table1 order by id.
I’m assuming data should go like 1,2,3,4 but its not the case always. Everytime it goes in different order say 1,3,2,4 or 1,2,3,4 or 4,3,2,1 or 1,3,4,2
Could you please suggest on that,
Create a Clustered Index in table2 on column id
Be careful here. If I read what it sounds like you are saying, you are suggesting to create this clustered index so the rows in table2 will be "ordered" correctly? There are times when you really do want an order by for an insert (if there is an identity on the target). However sql will still store this data in what it finds the most convenient. If you want your data from table2 to be returned in a certain order there is 1 and only 1 way to achieve this...use an order by when you pull the data out.
We got very good point here to discuss.I agree with Sean in case there are lot of DML operations on the table but if it is not the case like the table is basically used for Reporting purpose (it may be the case as Mahesh is getting the data from one table to another) then order by clause may cost him a lot to fetch many records.While a clustered index will certainly reduce the execution time for report query.
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June 29, 2012 at 12:17 am
The clustered index will still not guarantee the order of the data when output via a select statement.
The only way to guarantee the order of the data is to use an ORDER BY clause.
June 29, 2012 at 4:07 am
Lynn Pettis (6/29/2012)
The clustered index will still not guarantee the order of the data when output via a select statement.The only way to guarantee the order of the data is to use an ORDER BY clause.
I appreciate your and Sean's response.
The below article helped me to understand how things work in such a case.
"SQL Server will make effort to create it in a contiguous manner ... but there are no guarantees..."
http://www.sqlmag.com/article/sql-server/quaere-verum-clustered-index-scans-part-i
June 29, 2012 at 4:06 pm
I am not sure that I understand why you would want to control the order of insert. If there were a column in table 1 that you wanted to control the table 2 order you could do that with an index. I would agree that the best way to control the order of a result set is to use and order by on the select from table 2.
SQL is going to attempt to accomplish the insert into the b table as set of rows. If you must subvert this you could write a cursor that steps thru table 1 and to single inserts into table 2. While this may be the worst possible way from a performance perspective it would guarantee the insert order.
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