To start, take this snippet as an example:
SELECT *
FROM StatsVehicle
WHERE ((ReferenceMakeId = #referenceMakeId)
OR #referenceMakeId IS NULL)
This will fetch and filter the records if the variable #referenceMakeId is not null, and if it is null, will fetch all the records. In other words, it is taking the first one into consideration if #referenceMakeId is not null.
I would like to add a further restriction to this, how can I achieve this?
For instance
(ReferenceModelId = #referenceModeleId) OR
(
(ReferenceMakeId = #referenceMakeId) OR
(#referenceMakeId IS NULL)
)
If #referenceModelId is not null, it will only need to filter by ReferenceModelId, and ignore the other statements inside it. If I actually do this as such, it returns all the records. Is there anything that can be done to achieve such a thing?
Maybe something like this?
SELECT * FROM StatsVehicle WHERE
(
-- Removed the following, as it's not clear if this is beneficial
-- (#referenceModeleId IS NOT NULL) AND
(ReferenceModelId = #referenceModeleId)
) OR
(#referenceModeleId IS NULL AND
(
(ReferenceMakeId = #referenceMakeId) OR
(#referenceMakeId IS NULL)
)
)
This should do the trick.
SELECT * FROM StatsVehicle
WHERE ReferenceModelId = #referenceModeleId OR
(
#referenceModeleId IS NULL AND
(
#referenceMakeId IS NULL OR
ReferenceMakeId = #referenceMakeId
)
)
However, you should note that this types of queries (known as catch-all queries) tend to be less efficient then writing a single query for every case.
This is due to the fact that SQL Server will cache the first query plan that might not be optimal for other parameters.
You might want to consider using the OPTION (RECOMPILE) query hint, or braking down the stored procedure to pieces that will each handle the specific conditions (i.e one select for null variables, one select for non-null).
For more information, read this article.
If #referenceModelId is not null, it will only need to filter by
ReferenceModelId, and ignore the other statements inside it. If I
actually do this as such, it returns all the records. Is there
anything that can be done to achieve such a thing?
You can think of using a CASE for good short circuit mechanism
WHERE
CASE
WHEN #referenceModelId is not null AND ReferenceModelId = #referenceModeleId THEN 1
WHEN #referenceMakeId is not null AND ReferenceMakeId = #referenceMakeId THEN 1
WHEN #referenceModelId is null AND #referenceMakeId is null THEN 1
ELSE 0
END = 1
Related
So I'm creating a query for a report that could have several optional filters. I've only included client and station here to keep it simple. Each of these options could be an include or an exclude and could contain NULL, 1, or multiple values. So I split the varchar into a table before joining it to the query.
This test takes about 15 minutes to execute, which... just won't do :p Is there a better way? We have similar queries written with dynamic sql, and I was trying to avoid that, but maybe there's no way around it for this?
DECLARE
#ClientsInc VARCHAR(10) = 'ABCD, EFGH',
#ClientsExc VARCHAR(10) = NULL,
#StationsInc VARCHAR(10) = NULL,
#StationsExc VARCHAR(10) = 'SomeStation'
SELECT *
INTO #ClientsInc
FROM dbo.StringSplit(#ClientsInc, ',')
SELECT *
INTO #ClientsExc
FROM dbo.StringSplit(#ClientsExc, ',')
SELECT *
INTO #StationsInc
FROM dbo.StringSplit(#StationsInc, ',')
SELECT *
INTO #StationsExc
FROM dbo.StringSplit(#StationsExc, ',')
SELECT [some stuff]
FROM media_order mo
LEFT JOIN #ClientsInc cInc WITH(NOLOCK) ON cInc.Value = mo.client_code
LEFT JOIN #ClientsExc cExc WITH(NOLOCK) ON cExc.Value = mo.client_code
LEFT JOIN #StationsInc sInc WITH(NOLOCK) ON sInc.Value = mo.station_name
LEFT JOIN #StationsExc sExc WITH(NOLOCK) ON sExc.Value = mo.station_name
WHERE ((#ClientsInc IS NOT NULL AND cInc.Value IS NOT NULL)
OR (#ClientsExc IS NOT NULL AND cExc.Value IS NULL)
)
AND ((#StationsInc IS NOT NULL AND sInc.Value IS NOT NULL)
OR (#StationsExc IS NOT NULL AND sExc.Value IS NULL)
)
First of all, I always tend to mention Erland Sommarskog's Dynamic Search Conditions in such cases.
However, you already seem to be aware of the two options: one is dynamic SQL. The other is usually the old trick and (#var is null or #var=respective_column). This trick, however, works only for one value per variable.
Your solution indeed seems to work for multiple values. But in my opinion, you are trying too hard to avoid dynamic sql. Your requirements are complex enough to guarantee it. And remember, usually, dynamic sql is harder for you to code, but easier for the server in complex cases - and this one certainly is. Making a performance guess is always risky, but I would guess an improvement in this case.
I would use exists and not exists:
select ...
from media_order mo
where
(
#ClientsInc is null
or exists (
select 1
from string_split(#ClientsInc, ',')
where value = mo.client_code
)
)
and not exist (
select 1
from string_split(#ClientsExc, ',')
where value = mo.client_code
)
and (
#StationsInc is null
or exists (
select 1
from string_split(#StationsInc, ',')
where value = mo.station_name
)
)
and not exist (
select 1
from string_split(#StationsExc, ',')
where value = mo.station_name
)
Notes:
I used buil-in function string_split() rather than the custom splitter that you seem to be using. It is available in SQL Server 2016 and higher, and returns a single column called value. You can change that back to your customer function if you are running an earlier version
as I understand the logic you want, "include" parameters need to be checked for nullness before using exists, while it is unnecessary for "exclude" variables
I would like to pass in a parameter #CompanyID into a where clause to filter results. But sometimes this value may be null so I want all records to be returned. I have found two ways of doing this, but am not sure which one is the safest.
Version 1
SELECT ProductName, CompanyID
FROM Products
WHERE (#CompanyID IS NULL OR CompanyID = #CompanyID)
Version 2
SELECT ProductName, CompanyID
FROM Products
WHERE CompanyID = COALESCE(#CompanyID, CompanyID)
I have found that the first version is the quickest, but I have also found in other tables using a similar method that I get different result sets back. I don't quite understand the different between the two.
Can anyone please explain?
Well, both queries are handling the same two scenarios -
In one scenario #CompanyID contains a value,
and in the second #CompanyID contains NULL.
For both queries, the first scenario will return the same result set - since
if #CompanyId contains a value, both will return all rows where companyId = #CompanyId, however the first query might return it faster (more on that at the end of my answer).
The second scenario, however, is where the queries starts to behave differently.
First, this is why you get different result sets:
Difference in result sets
Version 1
WHERE (#CompanyID IS NULL OR CompanyID = #CompanyID)
When #CompanyID is null, the where clause will not filter out any rows whatsoever, and all the records in the table will be returned.
Version 2
WHERE CompanyID = COALESCE(#CompanyID, CompanyID)
When #CompanyID is null, the where clause will filter out all the rows where CompanyID is null, since the result of null = null is actually unknown - and any query with null = null as it's where clause will return no results, unless ANSI_NULLS is set to OFF (which you really should not do since it's deprecated).
Index usage
You might get faster results from the first version, since the use of any function on a column in the where clause will prevent SQL Server from using any index that you might have on this column.
You can read more about it on this article in MSSql Tips.
Conclusion
Version 1 is better than version 2.
Even if you do not want to return records where companyId is null it's still better to write as WHERE (#CompanyID IS NULL OR CompanyID = #CompanyID) AND CompanyID IS NOT NULL than to use the second version.
It's worth noting that using the syntax ([Column] = #Value OR [Column] IS NULL) is a much better idea than using ISNULL([Column],#Value) = #Value (or using COALESCE).
This is because using the function causes the query to become un-SARGable; so indexes won't be used. The first expression is SARGable, and thus, will perform better.
Just adding this, as the OP states "I have found that the first version is the quickest", and wanted to elaborate why (even though, currently the statement is incomplete, I am guessing this was more due to user error and ignorance).
The second version is not correct SQL (for SQL Server). It needs an operator. Presumably:
SELECT ProductName, CompanyID
FROM Products
WHERE COALESCE(#CompanyID, CompanyID) = CompanyID;
The first version is correct as written. If you have an index on CompanyID, you might find this faster:
SELECT *
FROM Products
WHERE CompanyID = #CompanyID
UNION ALL
SELECT *
FROM Products
WHERE #CompanyID IS NULL;
I have a bit of SQL that queries a table that has one column that can take NULL.
In the code below the #term_type_id could be NULL, and the column term_type_id could have NULL values.
So the code below works if #term_type_id has a value, but does not work if #term_type_id is NULL.
Setting SET ANSI_NULLS OFF is a way around the problem, but I do know that this will be depreciated at some stage.
SELECT [date],value FROM history
WHERE id=#id
AND data_type_id=#data_type_id
AND quote_type_id=#quote_type_id
AND update_type_id=#update_type_id
AND term_type_id=#term_type_id
AND source_id=#source_id
AND ([date]>=#temp_from_date and [date]<=#temp_to_date)
ORDER BY [date]
What I have done in the past is to have something like this
if #term_type_id is NULL
BEGIN
SELECT ......
WHERE .....
AND term_type_id IS NULL
END
BEGIN
SELECT ......
WHERE .....
AND term_type_id = #term_type_id
END
While this works, it is very verbose and makes the code hard to read and maintain.
Does anyone have a better solution than using SET ANSI_NULLS OFF or having to write conditional code just to manage the case when something could be a value or NULL?
BTW - When I use SET ANSI_NULLS OFF, I only do it for the specific query then turn it back on afterwards. I do understand the reasons why this is frowned upon, but it is at the expense of writing pointless code to get around a 'pure' view of NULL.
Ben
Since both the column and the parameter can be null, you should treat both cases:
SELECT [date],value FROM history
WHERE id=#id
AND data_type_id=#data_type_id
AND quote_type_id=#quote_type_id
AND update_type_id=#update_type_id
AND ((term_type_id IS NULL AND #term_type_id IS NULL) OR term_type_id = #term_type_id)
AND source_id=#source_id
AND ([date]>=#temp_from_date and [date]<=#temp_to_date)
ORDER BY [date]
Note that this will only return results when both column and parameter are null, or none of them is null.
Ben, a better solution to if #term_type_id is NULL SELECT #term_type_id=-1
would be to use isnull(#term_type_id,-1)
Ahh - yes - thank you for the prompt responses. I think I have just come up with a better solution (well in this case)...
if #term_type_id is NULL SELECT #term_type_id=-1
SELECT [date],value FROM history
WHERE id=#id
AND data_type_id=#data_type_id
AND quote_type_id=#quote_type_id
AND update_type_id=#update_type_id
AND ISNULL(term_type_id,-1)=#term_type_id
AND source_id=#source_id
AND ([date]>=#temp_from_date and [date]<=#temp_to_date)
ORDER BY [date]
This works in this case as term_type_id is the result of an identity (1,1) and thus can not be -1.
Try this, this will work on both case.
SELECT ......
WHERE .....
AND ISNULL(term_type_id,-1) = ISNULL(#term_type_id,-1)
You can use any static value instead of -1
Or you can use something like below
SELECT ......
WHERE .....
AND ( (#term_type_id IS NULL AND term_type_id IS NULL)
OR term_type_id = #term_type_id
)
If it's the only nullable column among your search criteria, the best way would be to split conditions within a single UNION statement:
select date, value from dbo.History
where term_type_id is null
-- Remaining search criteria
and ...
union all
select date, value from dbo.History
where term_type_id = #term_type_id
-- Remaining search criteria
and ...
This is the fastest code possible in your case, basically because SQL Server doesn't have a particular knack for OR-ed conditions. However, another nullable column will turn this into a rather unpleasant mess.
If you think you can sacrifice performance, there is a useful function in T-SQL that does exactly that - NULLIF():
select date, value from dbo.History
where nullif(#term_type_id, term_type_id) is null
-- Remaining search criteria
and ...
However, this type of condition will be non-SARGable, most likely. Also, note that the order of arguments does matter in NULLIF(). Alternatively, you can devise CASE constructs of various complexity that might be semantically more suitable to your exact requirements.
I use this pattern for optional filter paramaters in my SQL Stored Procedures
AND (
#OptionalParam IS NULL OR
(
Id = #OptionalParam
)
)
However the OR is not a friend of the query optimizer. Is there a more efficient way to do this without using dynamic SQL
You can try using COALESCE. Not sure if it will be more efficient.
AND Id = Coalesce(#OptionalParam, Id)
This will not work if Id itself is null and you are using ANSI nulls.
AND ID = ISNULL(#OptionalParam, ID)
or you if you had multiple optional parameters can use
AND ID = COALESCE(#OptionalParam1, #OptionalParam2, ID)
This is definitely faster than using an OR statement.
Like the other answerer mentioned, this will not work if the ID column is null (but then again, the original statement wouldn't either).
You could try:
AND Id = CASE WHEN #OptionalParam IS NULL THEN Id ELSE NULL END
I doubt this will optimize much better, but there's no OR in it.
Alternatively, you could break your query apart into two components -- one with just an #OptionalParam IS NULL test and another with an Id = #OptionalParam test, then UNION them together. Depending on your data topology this might yield better results. It could also be significantly worse.
I have a stored procedure that will query and return records based on if items are available or not. That part is easy, Im simply passing in a variable to check where available is yes or no.
But what I want to know is how do I throw a everything clause in there (i.e available, not available, or everything)?
The where clause right now is
where availability = #availability
The values of availabitility are either 1 or 0, nothing else.
You can use NULL to represent everything.
WHERE (#availability IS NULL OR availability = #availability)
SELECT *
FROM mytable
WHERE #availability IS NULL
UNION ALL
SELECT *
FROM mytable
WHERE availability = #availability
Passing a NULL value will select everything.
This query will use an index on availability if any.
Don't know the type of #availability, but assuming -1 = everything then you could simply do a
where #availability = -1 OR availability = #availability
multiple ways of doing it. Simpliest way is is to set the default value of the #availability to null and then your where clause would look like this
WHERE (#availability IS NULL OR availability = #availability)