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sql server programming
group:When do functions get applied?
sql server programming:
Given a statement such as this:
SELECT myUDF(ColumnA), ColumnB FROM tableQ WHERE ColumnB = 'SomeValue' Does the myUDF function still get executed against every record in the table, even though the WHERE clause contains enough information to allow the myUDF function to execute against only the filtered subset of records that would be returned? I could understand that a slightly modified version of it... SELECT ColumnA, ColumnB FROM tableQ WHERE myUDF(ColumnB) = 'SomeTransformedValue' ....would actually require that the function is executed against every record to evaluate the condition. But what would the behavior be on the former example? To beat the dead horse, I would expect SQL to be smart enough to only execute that function once if given the following syntax: SELECT TOP 1 myUDF(ColumnA) FROM tableQ The answer will help me determine whether I want to take a user defined function approach to manipulating some values or if I'll push this manupulation back to my business layer... Thanks in advance!
A UDF that converts the stored UTC datetime to the localtime of a specific
time zone. It returns a single nvarchar. [quoted text, click to view] "Uri Dimant" wrote:
> Matt > What kind of UDF do you have ? > http://www.sql-server-performance.com/user_defined_functions.asp > > > > > > "Matt" <Matt@discussions.microsoft.com> wrote in message > news:C2A75BF7-8D42-4EEF-98E4-73083A23EB74@microsoft.com... > > Given a statement such as this: > > > > SELECT myUDF(ColumnA), ColumnB > > FROM tableQ > > WHERE ColumnB = 'SomeValue' > > > > Does the myUDF function still get executed against every record in the > > table, even though the WHERE clause contains enough information to allow > > the > > myUDF function to execute against only the filtered subset of records that > > would be returned? > > > > I could understand that a slightly modified version of it... > > > > SELECT ColumnA, ColumnB > > FROM tableQ > > WHERE myUDF(ColumnB) = 'SomeTransformedValue' > > > > ...would actually require that the function is executed against every > > record > > to evaluate the condition. But what would the behavior be on the former > > example? > > > > To beat the dead horse, I would expect SQL to be smart enough to only > > execute that function once if given the following syntax: > > > > SELECT TOP 1 myUDF(ColumnA) > > FROM tableQ > > > > > > The answer will help me determine whether I want to take a user defined > > function approach to manipulating some values or if I'll push this > > manupulation back to my business layer... > > > > Thanks in advance! > > Matt > >
I did read the article, yes. I am aware of the potential for performance
hits. Thank you for your reply. [quoted text, click to view] "Uri Dimant" wrote:
> Matt > I hope you read the article I have posted here > > SELECT myUDF(ColumnA), ColumnB > FROM tableQ > WHERE ColumnB = 'SomeValue' > > In that case an UDF will be executed for each rows in the table that > matching to the WHERE condition > > > > > "Matt" <Matt@discussions.microsoft.com> wrote in message > news:7A6BC4E0-2770-4788-8ED7-6EA712C4393B@microsoft.com... > >A UDF that converts the stored UTC datetime to the localtime of a specific > > time zone. It returns a single nvarchar. > > > > "Uri Dimant" wrote: > > > >> Matt > >> What kind of UDF do you have ? > >> http://www.sql-server-performance.com/user_defined_functions.asp > >> > >> > >> > >> > >> > >> "Matt" <Matt@discussions.microsoft.com> wrote in message > >> news:C2A75BF7-8D42-4EEF-98E4-73083A23EB74@microsoft.com... > >> > Given a statement such as this: > >> > > >> > SELECT myUDF(ColumnA), ColumnB > >> > FROM tableQ > >> > WHERE ColumnB = 'SomeValue' > >> > > >> > Does the myUDF function still get executed against every record in the > >> > table, even though the WHERE clause contains enough information to > >> > allow > >> > the > >> > myUDF function to execute against only the filtered subset of records > >> > that > >> > would be returned? > >> > > >> > I could understand that a slightly modified version of it... > >> > > >> > SELECT ColumnA, ColumnB > >> > FROM tableQ > >> > WHERE myUDF(ColumnB) = 'SomeTransformedValue' > >> > > >> > ...would actually require that the function is executed against every > >> > record > >> > to evaluate the condition. But what would the behavior be on the > >> > former > >> > example? > >> > > >> > To beat the dead horse, I would expect SQL to be smart enough to only > >> > execute that function once if given the following syntax: > >> > > >> > SELECT TOP 1 myUDF(ColumnA) > >> > FROM tableQ > >> > > >> > > >> > The answer will help me determine whether I want to take a user defined > >> > function approach to manipulating some values or if I'll push this > >> > manupulation back to my business layer... > >> > > >> > Thanks in advance! > >> > Matt > >> > >> > >> > >
Matt
What kind of UDF do you have ? http://www.sql-server-performance.com/user_defined_functions.asp [quoted text, click to view] "Matt" <Matt@discussions.microsoft.com> wrote in message news:C2A75BF7-8D42-4EEF-98E4-73083A23EB74@microsoft.com... > Given a statement such as this: > > SELECT myUDF(ColumnA), ColumnB > FROM tableQ > WHERE ColumnB = 'SomeValue' > > Does the myUDF function still get executed against every record in the > table, even though the WHERE clause contains enough information to allow > the > myUDF function to execute against only the filtered subset of records that > would be returned? > > I could understand that a slightly modified version of it... > > SELECT ColumnA, ColumnB > FROM tableQ > WHERE myUDF(ColumnB) = 'SomeTransformedValue' > > ...would actually require that the function is executed against every > record > to evaluate the condition. But what would the behavior be on the former > example? > > To beat the dead horse, I would expect SQL to be smart enough to only > execute that function once if given the following syntax: > > SELECT TOP 1 myUDF(ColumnA) > FROM tableQ > > > The answer will help me determine whether I want to take a user defined > function approach to manipulating some values or if I'll push this > manupulation back to my business layer... > > Thanks in advance! > Matt
Matt
I hope you read the article I have posted here SELECT myUDF(ColumnA), ColumnB FROM tableQ WHERE ColumnB = 'SomeValue' In that case an UDF will be executed for each rows in the table that matching to the WHERE condition [quoted text, click to view] "Matt" <Matt@discussions.microsoft.com> wrote in message news:7A6BC4E0-2770-4788-8ED7-6EA712C4393B@microsoft.com... >A UDF that converts the stored UTC datetime to the localtime of a specific > time zone. It returns a single nvarchar. > > "Uri Dimant" wrote: > >> Matt >> What kind of UDF do you have ? >> http://www.sql-server-performance.com/user_defined_functions.asp >> >> >> >> >> >> "Matt" <Matt@discussions.microsoft.com> wrote in message >> news:C2A75BF7-8D42-4EEF-98E4-73083A23EB74@microsoft.com... >> > Given a statement such as this: >> > >> > SELECT myUDF(ColumnA), ColumnB >> > FROM tableQ >> > WHERE ColumnB = 'SomeValue' >> > >> > Does the myUDF function still get executed against every record in the >> > table, even though the WHERE clause contains enough information to >> > allow >> > the >> > myUDF function to execute against only the filtered subset of records >> > that >> > would be returned? >> > >> > I could understand that a slightly modified version of it... >> > >> > SELECT ColumnA, ColumnB >> > FROM tableQ >> > WHERE myUDF(ColumnB) = 'SomeTransformedValue' >> > >> > ...would actually require that the function is executed against every >> > record >> > to evaluate the condition. But what would the behavior be on the >> > former >> > example? >> > >> > To beat the dead horse, I would expect SQL to be smart enough to only >> > execute that function once if given the following syntax: >> > >> > SELECT TOP 1 myUDF(ColumnA) >> > FROM tableQ >> > >> > >> > The answer will help me determine whether I want to take a user defined >> > function approach to manipulating some values or if I'll push this >> > manupulation back to my business layer... >> > >> > Thanks in advance! >> > Matt >> >> >>
[quoted text, click to view]
> SELECT myUDF(ColumnA), ColumnB > FROM tableQ > WHERE ColumnB = 'SomeValue' > > Does the myUDF function still get executed against every record in the > table, even though the WHERE clause contains enough information to allow the > myUDF function to execute against only the filtered subset of records that > would be returned? It will be evaluated for only the rows that matches your condition. -- Tibor Karaszi, SQL Server MVP http://www.karaszi.com/sqlserver/default.asp http://www.solidqualitylearning.com/ [quoted text, click to view] "Matt" <Matt@discussions.microsoft.com> wrote in message news:C2A75BF7-8D42-4EEF-98E4-73083A23EB74@microsoft.com... > Given a statement such as this: > > SELECT myUDF(ColumnA), ColumnB > FROM tableQ > WHERE ColumnB = 'SomeValue' > > Does the myUDF function still get executed against every record in the > table, even though the WHERE clause contains enough information to allow the > myUDF function to execute against only the filtered subset of records that > would be returned? > > I could understand that a slightly modified version of it... > > SELECT ColumnA, ColumnB > FROM tableQ > WHERE myUDF(ColumnB) = 'SomeTransformedValue' > > ...would actually require that the function is executed against every record > to evaluate the condition. But what would the behavior be on the former > example? > > To beat the dead horse, I would expect SQL to be smart enough to only > execute that function once if given the following syntax: > > SELECT TOP 1 myUDF(ColumnA) > FROM tableQ > > > The answer will help me determine whether I want to take a user defined > function approach to manipulating some values or if I'll push this > manupulation back to my business layer... > > Thanks in advance! > Matt
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