Does it make a difference to performance if you join tables in a chain VS joining to a central table?
0
In a real scenario, there may be more tables, each having many columns.
Here is a greatly simplified example. If I join my tables like this:
Would there be any difference if I joined the tables like this:
I could test it for one particular case, but that wouldn't tell me if there is NEVER a difference, or if it depends on the exact query/data in each table.
My instinct tells me that it shouldn't make a difference, and the execution plan would be identical either way, but I would like someone to confirm that if possible.
sql-server join asked Nov 28 '18 at 15:02
GravitateGravitate
1,3921326
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show 1 more comment
0
In a real scenario, there may be more tables, each having many columns.
Here is a greatly simplified example. If I join my tables like this:
Would there be any difference if I joined the tables like this:
I could test it for one particular case, but that wouldn't tell me if there is NEVER a difference, or if it depends on the exact query/data in each table.
My instinct tells me that it shouldn't make a difference, and the execution plan would be identical either way, but I would like someone to confirm that if possible.
sql-server join asked Nov 28 '18 at 15:02
GravitateGravitate
1,3921326
1
There's really no way to answer this without examples of real schema and data. These are completely different queries, though. As it is in your example, it won't be long / take a ton of data in each table before each yields very different results.
– squillman
Nov 28 '18 at 15:07
2
DO NOT make design decisions for performance. You make design decisions to best model the data. Those two designs you posted are vastly different. You are going down the path of premature optimization which is the root of all evil.
– Sean Lange
Nov 28 '18 at 15:08
@SeanLange I'm sorry, I should have made it clear that the layout is only a view. The tables already exist. The design is already in place. The same ID's happen to exist in the tables and can be linked in the views in either configuration. So it's not really designing for performance. I am merely curious as to which approach would be preferred, or if it would make no actual difference.
– Gravitate
Nov 28 '18 at 15:34
Then why not create both queries and look at the execution plan. I would strongly advise you to NOT use the view designer. It does some really interesting things.
– Sean Lange
Nov 28 '18 at 15:35
@SeanLange Yes, as I say in the question, I could do that, however, that wouldn't tell me if it ALWAYS resulted in the same execution plan. Just because it happened to result in the same execution plan in my one test case, it doesn't mean that there aren't many cases where it would be different. I understand what you mean about the query designer, however, I thought it would be useful as an illustration.
– Gravitate
Nov 28 '18 at 15:40
|
show 1 more comment
0
0
0
In a real scenario, there may be more tables, each having many columns.
Here is a greatly simplified example. If I join my tables like this:
Would there be any difference if I joined the tables like this:
I could test it for one particular case, but that wouldn't tell me if there is NEVER a difference, or if it depends on the exact query/data in each table.
My instinct tells me that it shouldn't make a difference, and the execution plan would be identical either way, but I would like someone to confirm that if possible.
sql-server join asked Nov 28 '18 at 15:02
GravitateGravitate
1,3921326
In a real scenario, there may be more tables, each having many columns.
Here is a greatly simplified example. If I join my tables like this:
Would there be any difference if I joined the tables like this:
I could test it for one particular case, but that wouldn't tell me if there is NEVER a difference, or if it depends on the exact query/data in each table.
My instinct tells me that it shouldn't make a difference, and the execution plan would be identical either way, but I would like someone to confirm that if possible.
sql-server join sql-server join asked Nov 28 '18 at 15:02
GravitateGravitate
1,3921326
asked Nov 28 '18 at 15:02
GravitateGravitate
1,3921326
asked Nov 28 '18 at 15:02
GravitateGravitate
1,3921326
asked Nov 28 '18 at 15:02
GravitateGravitate
1,3921326
asked Nov 28 '18 at 15:02
GravitateGravitate
1,3921326
1,3921326
1
There's really no way to answer this without examples of real schema and data. These are completely different queries, though. As it is in your example, it won't be long / take a ton of data in each table before each yields very different results.
– squillman
Nov 28 '18 at 15:07
2
DO NOT make design decisions for performance. You make design decisions to best model the data. Those two designs you posted are vastly different. You are going down the path of premature optimization which is the root of all evil.
– Sean Lange
Nov 28 '18 at 15:08
@SeanLange I'm sorry, I should have made it clear that the layout is only a view. The tables already exist. The design is already in place. The same ID's happen to exist in the tables and can be linked in the views in either configuration. So it's not really designing for performance. I am merely curious as to which approach would be preferred, or if it would make no actual difference.
– Gravitate
Nov 28 '18 at 15:34
Then why not create both queries and look at the execution plan. I would strongly advise you to NOT use the view designer. It does some really interesting things.
– Sean Lange
Nov 28 '18 at 15:35
@SeanLange Yes, as I say in the question, I could do that, however, that wouldn't tell me if it ALWAYS resulted in the same execution plan. Just because it happened to result in the same execution plan in my one test case, it doesn't mean that there aren't many cases where it would be different. I understand what you mean about the query designer, however, I thought it would be useful as an illustration.
– Gravitate
Nov 28 '18 at 15:40
|
show 1 more comment
1
There's really no way to answer this without examples of real schema and data. These are completely different queries, though. As it is in your example, it won't be long / take a ton of data in each table before each yields very different results.
– squillman
Nov 28 '18 at 15:07
2
DO NOT make design decisions for performance. You make design decisions to best model the data. Those two designs you posted are vastly different. You are going down the path of premature optimization which is the root of all evil.
– Sean Lange
Nov 28 '18 at 15:08
@SeanLange I'm sorry, I should have made it clear that the layout is only a view. The tables already exist. The design is already in place. The same ID's happen to exist in the tables and can be linked in the views in either configuration. So it's not really designing for performance. I am merely curious as to which approach would be preferred, or if it would make no actual difference.
– Gravitate
Nov 28 '18 at 15:34
Then why not create both queries and look at the execution plan. I would strongly advise you to NOT use the view designer. It does some really interesting things.
– Sean Lange
Nov 28 '18 at 15:35
@SeanLange Yes, as I say in the question, I could do that, however, that wouldn't tell me if it ALWAYS resulted in the same execution plan. Just because it happened to result in the same execution plan in my one test case, it doesn't mean that there aren't many cases where it would be different. I understand what you mean about the query designer, however, I thought it would be useful as an illustration.
– Gravitate
Nov 28 '18 at 15:40
1
1
There's really no way to answer this without examples of real schema and data. These are completely different queries, though. As it is in your example, it won't be long / take a ton of data in each table before each yields very different results.
– squillman
Nov 28 '18 at 15:07
There's really no way to answer this without examples of real schema and data. These are completely different queries, though. As it is in your example, it won't be long / take a ton of data in each table before each yields very different results.
– squillman
Nov 28 '18 at 15:07
2
2
DO NOT make design decisions for performance. You make design decisions to best model the data. Those two designs you posted are vastly different. You are going down the path of premature optimization which is the root of all evil.
– Sean Lange
Nov 28 '18 at 15:08
DO NOT make design decisions for performance. You make design decisions to best model the data. Those two designs you posted are vastly different. You are going down the path of premature optimization which is the root of all evil.
– Sean Lange
Nov 28 '18 at 15:08
@SeanLange I'm sorry, I should have made it clear that the layout is only a view. The tables already exist. The design is already in place. The same ID's happen to exist in the tables and can be linked in the views in either configuration. So it's not really designing for performance. I am merely curious as to which approach would be preferred, or if it would make no actual difference.
– Gravitate
Nov 28 '18 at 15:34
@SeanLange I'm sorry, I should have made it clear that the layout is only a view. The tables already exist. The design is already in place. The same ID's happen to exist in the tables and can be linked in the views in either configuration. So it's not really designing for performance. I am merely curious as to which approach would be preferred, or if it would make no actual difference.
– Gravitate
Nov 28 '18 at 15:34
Then why not create both queries and look at the execution plan. I would strongly advise you to NOT use the view designer. It does some really interesting things.
– Sean Lange
Nov 28 '18 at 15:35
Then why not create both queries and look at the execution plan. I would strongly advise you to NOT use the view designer. It does some really interesting things.
– Sean Lange
Nov 28 '18 at 15:35
@SeanLange Yes, as I say in the question, I could do that, however, that wouldn't tell me if it ALWAYS resulted in the same execution plan. Just because it happened to result in the same execution plan in my one test case, it doesn't mean that there aren't many cases where it would be different. I understand what you mean about the query designer, however, I thought it would be useful as an illustration.
– Gravitate
Nov 28 '18 at 15:40
@SeanLange Yes, as I say in the question, I could do that, however, that wouldn't tell me if it ALWAYS resulted in the same execution plan. Just because it happened to result in the same execution plan in my one test case, it doesn't mean that there aren't many cases where it would be different. I understand what you mean about the query designer, however, I thought it would be useful as an illustration.
– Gravitate
Nov 28 '18 at 15:40
|
show 1 more comment
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1
There's really no way to answer this without examples of real schema and data. These are completely different queries, though. As it is in your example, it won't be long / take a ton of data in each table before each yields very different results.
– squillman
Nov 28 '18 at 15:07
2
DO NOT make design decisions for performance. You make design decisions to best model the data. Those two designs you posted are vastly different. You are going down the path of premature optimization which is the root of all evil.
– Sean Lange
Nov 28 '18 at 15:08
@SeanLange I'm sorry, I should have made it clear that the layout is only a view. The tables already exist. The design is already in place. The same ID's happen to exist in the tables and can be linked in the views in either configuration. So it's not really designing for performance. I am merely curious as to which approach would be preferred, or if it would make no actual difference.
– Gravitate
Nov 28 '18 at 15:34
Then why not create both queries and look at the execution plan. I would strongly advise you to NOT use the view designer. It does some really interesting things.
– Sean Lange
Nov 28 '18 at 15:35
@SeanLange Yes, as I say in the question, I could do that, however, that wouldn't tell me if it ALWAYS resulted in the same execution plan. Just because it happened to result in the same execution plan in my one test case, it doesn't mean that there aren't many cases where it would be different. I understand what you mean about the query designer, however, I thought it would be useful as an illustration.
– Gravitate
Nov 28 '18 at 15:40