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Case statements advice - query case field?


Case statements advice - query case field?

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learning_sql
learning_sql
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Hi,


So basically I have three tables with three types of "things". Each of these tables have a column called "name". My fourth table contains references to these tables through an id field, only one of these tables will be related to the fourth table - I have produced the following SQL so the query has a name column which is populated by the related tables name.


SELECT
CASE
WHEN thing1.name IS NOT NULL THEN thing1.name
WHEN thing2.name IS NOT NULL THEN thing2.name
WHEN thing3.name IS NOT NULL THEN thing3.name
END AS name,
base.ls_id,
base.date_lease_start,
base.date_lease_end,
base.lease_term,
base.amount_current_rent
FROM base_table AS base
LEFT OUTER JOIN thing1_table AS thing1 ON base.as_id = thing1.as_id
LEFT OUTER JOIN thing2_table AS thing2 ON base.bl_id = thing2.bl_id
LEFT OUTER JOIN thing3_table AS thing3 ON base.ld_id = thing3.ld_id



That query works, my problem is the following, I hope to use the query in a SSRS report with a parameter enabling a search against the name column (which the case statement populates).

I would like to query the returned "name" column from that query - I could populate a temporary table however I would like to know what the "proper" way is for this?
Sean Lange
Sean Lange
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No need for a temp table here. Just add a where clause.


where thing1.name = @SearchVal
OR thing2.name = @SearchVal
OR thing3.name = @SearchVal



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learning_sql
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thanks, I was hoping for an easy answer and got it.

So there is no way to query the case's result itself, make sense but I wanted to be sure.
Sean Lange
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learning_sql (8/12/2013)
thanks, I was hoping for an easy answer and got it.

So there is no way to query the case's result itself, make sense but I wanted to be sure.


Of course there is a way. You could do something like this.


select * from
(
SELECT
CASE
WHEN thing1.name IS NOT NULL THEN thing1.name
WHEN thing2.name IS NOT NULL THEN thing2.name
WHEN thing3.name IS NOT NULL THEN thing3.name
END AS name,
base.ls_id,
base.date_lease_start,
base.date_lease_end,
base.lease_term,
base.amount_current_rent
FROM base_table AS base
LEFT OUTER JOIN thing1_table AS thing1 ON base.as_id = thing1.as_id
LEFT OUTER JOIN thing2_table AS thing2 ON base.bl_id = thing2.bl_id
LEFT OUTER JOIN thing3_table AS thing3 ON base.ld_id = thing3.ld_id
) x
where x.name = @SearchVal



_______________________________________________________________

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Read the article at http://www.sqlservercentral.com/articles/Best+Practices/61537/ for best practices on asking questions.

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Cross Tabs and Pivots, Part 1 – Converting Rows to Columns
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs
Understanding and Using APPLY (Part 1)
Understanding and Using APPLY (Part 2)
learning_sql
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SSRS doesn't like that method, never mind at least I have it working. Many thanks Sean.
Alan Burstein
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Instead of the case statement you can also do this:

SELECT ISNULL(thing1.name,(ISNULL(thing2.name,thing3.name))) AS name



-- Alan Burstein


Helpful links:

Best practices for getting help on SQLServerCentral -- Jeff Moden
How to Post Performance Problems -- Gail Shaw

Nasty fast set-based string manipulation functions:
For splitting strings try DelimitedSplit8K or DelimitedSplit8K_LEAD (SQL Server 2012+)
To split strings based on patterns try PatternSplitCM
Need to clean or transform a string? try NGrams, PatExclude8K, PatReplace8K, DigitsOnlyEE, or Translate8K

I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code. -- Itzik Ben-Gan 2001

dwain.c
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Alan.B (8/12/2013)
Instead of the case statement you can also do this:

SELECT ISNULL(thing1.name,(ISNULL(thing2.name,thing3.name))) AS name



And why not:


SELECT COALESCE(thing1.name,thing2.name,thing3.name) AS name




?


My mantra: No loops! No CURSORs! No RBAR! Hoo-uh!

My thought question: Have you ever been told that your query runs too fast?

My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.


Need to UNPIVOT? Why not CROSS APPLY VALUES instead?
Since random numbers are too important to be left to chance, let's generate some!
Learn to understand recursive CTEs by example.
Splitting strings based on patterns can be fast!
My temporal SQL musings: Calendar Tables, an Easter SQL, Time Slots and Self-maintaining, Contiguous Effective Dates in Temporal Tables
Alan Burstein
Alan Burstein
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Group: General Forum Members
Points: 32183 Visits: 8571
dwain.c (8/12/2013)
Alan.B (8/12/2013)
Instead of the case statement you can also do this:

SELECT ISNULL(thing1.name,(ISNULL(thing2.name,thing3.name))) AS name



And why not:


SELECT COALESCE(thing1.name,thing2.name,thing3.name) AS name




?


Nice. That is cleaner and easier to read.
+1

-- Alan Burstein


Helpful links:

Best practices for getting help on SQLServerCentral -- Jeff Moden
How to Post Performance Problems -- Gail Shaw

Nasty fast set-based string manipulation functions:
For splitting strings try DelimitedSplit8K or DelimitedSplit8K_LEAD (SQL Server 2012+)
To split strings based on patterns try PatternSplitCM
Need to clean or transform a string? try NGrams, PatExclude8K, PatReplace8K, DigitsOnlyEE, or Translate8K

I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code. -- Itzik Ben-Gan 2001

dwain.c
dwain.c
SSC-Forever
SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)

Group: General Forum Members
Points: 43731 Visits: 6431
Alan.B (8/12/2013)
dwain.c (8/12/2013)
Alan.B (8/12/2013)
Instead of the case statement you can also do this:

SELECT ISNULL(thing1.name,(ISNULL(thing2.name,thing3.name))) AS name



And why not:


SELECT COALESCE(thing1.name,thing2.name,thing3.name) AS name




?


Nice. That is cleaner and easier to read.
+1


I confess I don't use COALESCE myself very much but it is nice to know it is there for cases like this.


My mantra: No loops! No CURSORs! No RBAR! Hoo-uh!

My thought question: Have you ever been told that your query runs too fast?

My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.


Need to UNPIVOT? Why not CROSS APPLY VALUES instead?
Since random numbers are too important to be left to chance, let's generate some!
Learn to understand recursive CTEs by example.
Splitting strings based on patterns can be fast!
My temporal SQL musings: Calendar Tables, an Easter SQL, Time Slots and Self-maintaining, Contiguous Effective Dates in Temporal Tables
learning_sql
learning_sql
SSC Veteran
SSC Veteran (267 reputation)SSC Veteran (267 reputation)SSC Veteran (267 reputation)SSC Veteran (267 reputation)SSC Veteran (267 reputation)SSC Veteran (267 reputation)SSC Veteran (267 reputation)SSC Veteran (267 reputation)

Group: General Forum Members
Points: 267 Visits: 183
Thanks, those are much easier to read.

I have tested against SSRS, I will be using the coalesce query alongside the usual where clauses.

Thanks again.
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