Using USE does not set DB context

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Using USE does not set DB context

belal360

SSC Veteran

Points: 268
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June 10, 2024 at 9:25 pm

#4427557

Hi Experts,
I have a Sql file with a bunch of DDL statements (Create Tables/Views). I start with a DB then change DB context to another DB followed by 2nd set of DDLs.
In Sql file, I have:
DECLARE
@DB1 NVARCHAR(MAX) = 'DevDB',
@DB2 NVARCHAR(MAX) = 'TestDB',
@ENV NVARCHAR(MAX)
SELECT @ENV = 'USE ' + @DB1
EXEC (@ENV)
Issue is next line is CREATE TABLE does not get created in desired DB; as if DB context wasn't set.
Is there a way to have USE DevDB issued and followed statements are run in correct DB and same for the 2nd set of DDLs present in same Sql file??

Thanks in advance.

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Jeff Moden SSC Guru Points: 1004412 More actions · Answer 1

The Dynamic SQL is executed in a different context.

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

Jonathan AC Roberts SSCoach Points: 18363 More actions · Answer 2

Does your dynamic SQL get executed as one string?

e.g.:

SELECT @ENV = 'USE ' + @DB1
SET @ENV = @ENV + CHAR(13) + CHAR(10) + 'SELECT * FROM myTable;'
EXEC (@ENV)

belal360 SSC Veteran Points: 268 More actions · Answer 3

Thanks for the feedback.

Jon,

This is a code deploy script file, I'm trying to create. Hence, need to set DB context first then run a few DDLs (see below)

Example snippet:

SELECT @ENV = 'USE ' + @DB1

SET @ENV = @ENV + CHAR(13) + CHAR(10)

EXEC (@ENV)

CREATE TABLE T1;

CREATE TABLE T2;

CREATE VIEW V1; (cannot wrap all DDLs in a dynamic Sql as list is large)

Objects are not created as context does not persist. I cannot hardcode USE DBName due to ENV changes from Dev to test to Prod, Etc.

An alternate or workaround is appreciated.

Jonathan AC Roberts SSCoach Points: 18363 More actions · Answer 4

IF @DB1 = 'TestDB' USE TestDB
ELSE IF @DB1 = 'ProdDB'  USE ProdDB

frederico_fonseca SSCoach Points: 16167 More actions · Answer 5

belal360 wrote:

Thanks for the feedback.
Jon,
This is a code deploy script file, I'm trying to create. Hence, need to set DB context first then run a few DDLs (see below)
Example snippet:
SELECT @ENV = 'USE ' + @DB1 SET @ENV = @ENV + CHAR(13) + CHAR(10) EXEC (@ENV)
CREATE TABLE T1; CREATE TABLE T2; CREATE VIEW V1; (cannot wrap all DDLs in a dynamic Sql as list is large)
Objects are not created as context does not persist. I cannot hardcode USE DBName due to ENV changes from Dev to test to Prod, Etc.
An alternate or workaround is appreciated.

HOW exactly are you executing the scripts?

a rather standard way to do this is using sqlcmd - and on this particular case you can pass variables to sqlcmd which you can then use to replace text within the scripts.

frederico_fonseca SSCoach Points: 16167 More actions · Answer 6

Jonathan AC Roberts wrote:

IF @DB1 = 'TestDB' USE TestDB
ELSE IF @DB1 = 'ProdDB'  USE ProdDB

don't know what tool you are using to execute the above - but on SSMS it fails - and likely will fail as well with sqlcmd.

Jonathan AC Roberts SSCoach Points: 18363 More actions · Answer 7

frederico_fonseca wrote:

Jonathan AC Roberts wrote:
IF @DB1 = 'TestDB' USE TestDB
ELSE IF @DB1 = 'ProdDB'  USE ProdDB
don't know what tool you are using to execute the above - but on SSMS it fails - and likely will fail as well with sqlcmd.

You have to declare the variable and USE a database that actually exists.

DECLARE @DB1 varchar(20)
SET @DB1 = 'Test' -- Or set to 'Prod'
IF @DB1 = 'Test' USE TestDB
ELSE IF @DB1 = 'Prod'  USE ProdDB

What error do you get?

frederico_fonseca SSCoach Points: 16167 More actions · Answer 8

Jonathan AC Roberts wrote:

frederico_fonseca wrote:
Jonathan AC Roberts wrote:
IF @DB1 = 'TestDB' USE TestDB
ELSE IF @DB1 = 'ProdDB'  USE ProdDB
don't know what tool you are using to execute the above - but on SSMS it fails - and likely will fail as well with sqlcmd.
You have to declare the variable and USE a database that actually exists.
DECLARE @DB1 varchar(20)
SET @DB1 = 'Test' -- Or set to 'Prod'
IF @DB1 = 'Test' USE TestDB
ELSE IF @DB1 = 'Prod'  USE ProdDB
What error do you get?

well... you yourself clarified the point I was trying to make - that construct will never work for a deployment against different servers - a TEST db would not exist in the prod server - and reverse is true.

Jonathan AC Roberts SSCoach Points: 18363 More actions · Answer 9

frederico_fonseca wrote:

Jonathan AC Roberts wrote:
frederico_fonseca wrote:
Jonathan AC Roberts wrote:
IF @DB1 = 'TestDB' USE TestDB
ELSE IF @DB1 = 'ProdDB'  USE ProdDB
don't know what tool you are using to execute the above - but on SSMS it fails - and likely will fail as well with sqlcmd.
You have to declare the variable and USE a database that actually exists.
DECLARE @DB1 varchar(20)
SET @DB1 = 'Test' -- Or set to 'Prod'
IF @DB1 = 'Test' USE TestDB
ELSE IF @DB1 = 'Prod'  USE ProdDB
What error do you get?
well... you yourself clarified the point I was trying to make - that construct will never work for a deployment against different servers - a TEST db would not exist in the prod server - and reverse is true.

well... me myself, I just employ the time-honoured technique of chaining multiple USE statements with a healthy dose of 'GO' commands. It goes something like this:

GO
USE DevDb
GO
USE TestDb
GO
USE UatDb
GO
USE ProdDb
GO

Who needs database existence checks when you can just use brute force and persistence, right? It's the 'if-at-first-you-don't-succeed, USE, USE again' methodology!