How to set 1 database name containing a specific table to variable? - sql

Question

So, a little backstory on this one:
I have a lengthy query that I use frequently for my jobs that utilizes the sp_MSForEachDB stored proc. The query creates a temporary table, and then goes through and searches sys.tables, and if a database has a table called T_Study, it will run the query and pull these results into the temporary table.
What I am now trying to do is join in another table from another database, and this database is of a different type. These database are all distinguished by the existence T_BatchStores. All databases that have a T_BatchStores table will also have a table dbo.T_TSyntax, and this is the table on which I will need to join.
Essentially, I am trying to build a universal query that I can run on any server containing this software, and I have these few universal tables, but the names of the databases themselves will vary.
So what I want to do is, in my query that populates my temporary table, add the following:
JOIN '+#MEDDB+'.dbo.T_TSyntax and then my ON clause, etc. Keep in mind that this join occurs within my begin and end clauses and that sp_MSforEachDb will be run on this.
I want #MEDDB to be just a randomly selected name of ANY database on their SQL instance that contains a T_BatchStores table - it does not matter what the name is - I just don't want to modify the query every time I run it.
How can I use my DECLARE #MEDDB and SET/SELECT #MEDDB to work with these requirements?
Also, in some reading, I read that I should use SYSNAME as the data type, but I also know NVARCHAR would work - but I'd just like a tip on which would be ideal.
I have tried the following:
DECLARE #MEDDB SYSNAME
SET #MEDDB = (SELECT TOP 1 name FROM sys.databases WHERE EXISTS (SELECT name FROM sys.tables WHERE name = '''T_BATCHSTORES'''))
SELECT #MEDDB
But this returns 1 row with a NULL value. I'm very much a beginner to SQL, so any assistance would be greatly appreciated!
Note: I am only using Microsoft SQL Server 2008 and 2012 at the present time.
Thanks!
Okay, after heavily modifying the query so that the names aren't actually exactly the same as our actual table structure, here is a slimmed-down version of the query I'm using so that you'll see what I'm going for:
/* Add or change variables as needed and comment back in WHERE statements in Insert section as needed.
You do not need to delete any variables in this section, even if you do not need them.
Simply comment in or out relevant data in the WHERE clause in Section 4. */
/* Section 1: Declaring variables. */
DECLARE #STUID NVARCHAR (65)
DECLARE #IMUID NVARCHAR (200)
DECLARE #ACCN NVARCHAR (100)
DECLARE #MEDDB NVARCHAR (255)
/* Section 2: Assigning values to variables such as an Image file's UID. */
SET #STUID = 'enterSTUID'
SET #IMUID = 'enterIMUIDhere'
SET #ACCN = 'enterACCNhere'
SET #MEDDB = (SELECT TOP 1 name FROM sys.databases WHERE [name] LIKE '%med%'
AND [name] NOT LIKE '%audit%')
/* Section 3: Creating our temporary table to dump our results. */
IF OBJECT_ID('tempdb.dbo.#tempBatchResultsD6') IS NULL
BEGIN
CREATE TABLE #tempBatchResultsD6
(
Database_Name VARCHAR (200),
THING1 VARCHAR(100) NOT NULL,
THING2 VARCHAR(200) NOT NULL,
THING3 DATETIME NOT NULL,
TSyntaxUID VARCHAR (66) NOT NULL,
TSyntaxDesc VARCHAR (128) NOT NULL
)
END
TRUNCATE TABLE #tempBatchResultsD6
/* Section 4: Query that will be used to populate the contents of the temporary table created above.
Utilizing the stored procedure "sp_MSForEachDb," this will search every database on the SQL instance.
Here, we are limiting our results to only searching specific databases by only returning results from databases that have a "T_Studies" table. */
DECLARE #Command NVARCHAR(MAX)
SET #Command = N'USE [?];
IF EXISTS (SELECT * FROM sys.tables WHERE [name] = ''T_Studies'')
BEGIN
INSERT #tempBatchResultsD6
SELECT
DB_Name () as Database_Name,
THING1,
THING2,
THING3,
TS.TSyntaxUID,
TS.TSyntaxDesc
FROM T_Studies ST WITH (nolock)
JOIN T_Patients PT WITH (nolock) ON ST.ST_PT_FOLDERID = PT.PT_FOLDERID
JOIN T_Series SE WITH (nolock) ON ST.ST_FOLDERID = SE.SE_ST_FOLDERID
JOIN T_Images IM WITH (nolock) ON SE.SE_FOLDERID = IM.IM_SE_FOLDERID
JOIN '+#MEDDB+'.dbo.T_TSyntaxes TS WITH (nolock) on IM.IM_TSyntaxID = TS.TSyntaxUID
WHERE ST.STUID = '''+#STUID+'''
--WHERE IM.IM_UID = '''+#IMUID+'''
--WHERE ST.ST_ACCNNO = '''+#ACCN+'''
END'
EXEC sp_MSForEachDb #Command
/* Section 5: Querying our temporary table to get our results. */
SELECT
Database_Name,
THING1,
THING2,
THING3,
TSyntaxUID,
TSyntaxDesc
FROM #tempBatchResultsD6
ORDER BY Database_Name
So as you can see, this is a massive temp table that will pull from all databases that have a T_Studies table in them. It's huge in its actual form, but this is trimmed down significantly.
The problem comes in section 2, where I am using #MEDDB to choose a random database name if the name contains the word "Med" but not the word "audit." This is problematic because it assumes consistent naming across all sites - and while these names are suggested, they are never a guarantee.
To guarantee consistency, I am trying to populate the #MEDDB variable with the name of ANY database on their system that contains a T_BatchStores table instead of the WHERE [name] like portion.
Any advice with this new info would be greatly appreciated!

Answer 1

I am not sure whether I understand your question completely.
But if you wanna loop through all databases, you can use something like the following code. "SELECT XXX" would then be your query, by using "use ' + #DB_Name + ';" you switch to the desired database to execute the your query.
DECLARE #DB_Name varchar(100)
DECLARE #Command nvarchar(max)
DECLARE database_cursor CURSOR FOR
SELECT name
FROM MASTER.sys.sysdatabases
OPEN database_cursor
FETCH NEXT FROM database_cursor INTO #DB_Name
WHILE ##FETCH_STATUS = 0
BEGIN
set #Command =
'
use ' + #DB_Name + ';
SELECT XXX
'
EXEC sp_executesql #Command
FETCH NEXT FROM database_cursor INTO #DB_Name
END
CLOSE database_cursor
DEALLOCATE database_cursor

Answer 2

DECLARE #MEDDB NVARCHAR(500)
SET #MEDDB = 'SELECT TOP 1 name FROM sys.databases WHERE EXISTS (SELECT name FROM sys.tables WHERE name = ''T_BATCHSTORES'')'
EXEC (#MEDDB)
This is Dynamic SQL. Of course, I'm not getting any results, either, but I'm not in your database. Still, this allows you to be 'dynamic', and use a variable to modify things:
DECLARE #MEDDB NVARCHAR(500)
DECLARE #MEDDB2 NVARCHAR(100) = 'T_BATCHSTORES'
SET #MEDDB = 'SELECT TOP 1 name FROM sys.databases WHERE EXISTS (SELECT name FROM sys.tables WHERE name = ''' + #MEDDB2 + ''')'
EXEC (#MEDDB)
My recommendation is that you run simpler queries that show what you want, and then you build them into the dynamic method.
For instance, I'm in AdventureWorks right now, so I can do:
SELECT * FROM sys.databases
This gives me a list of all the databases that are available in here.
So maybe I expand that to
SELECT * FROM sys.databases WHERE name = 'AdventureWorks'
This gives me just one line of results. So if that's what I want, I build it into the dynamic portion:
DECLARE #MEDDB NVARCHAR(500)
DECLARE #MEDDB2 NVARCHAR(100) = 'AdventureWorks'
SET #MEDDB = 'SELECT * FROM sys.databases WHERE name =''' + #MEDDB2 + ''''
EXEC (#MEDDB)
It just all depends what you're looking for. I always find the data I want first, and then figure out how to make my query look for it.