有没有一种方法来持久化一个变量通过一个去？

有没有一种方法来持久化一个变量通过一个去？

Declare @bob as varchar(50);
Set @bob = 'SweetDB';
GO
USE @bob  --- see note below
GO
INSERT INTO @bob.[dbo].[ProjectVersion] ([DB_Name], [Script]) VALUES (@bob,'1.2')

请参阅“ USE@bob”行的 那么问题。

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最佳答案

The go command is used to split code into separate batches. If that is exactly what you want to do, then you should use it, but it means that the batches are actually separate, and you can't share variables between them.

In your case the solution is simple; you can just remove the go statements, they are not needed in that code.

Side note: You can't use a variable in a use statement, it has to be the name of a database.

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Use a temporary table:

CREATE TABLE #variables
(
VarName VARCHAR(20) PRIMARY KEY,
Value VARCHAR(255)
)
GO


Insert into #variables Select 'Bob', 'SweetDB'
GO


Select Value From #variables Where VarName = 'Bob'
GO


DROP TABLE #variables
go
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I prefer the this answer from this question Global Variables with GO

Which has the added benefit of being able to do what you originally wanted to do as well.

The caveat is that you need to turn on SQLCMD mode (under Query->SQLCMD) or turn it on by default for all query windows (Tools->Options then Query Results->By Default, open new queries in SQLCMD mode)

Then you can use the following type of code (completely ripped off from that same answer by Oscar E. Fraxedas Tormo)

--Declare the variable
:setvar MYDATABASE master
--Use the variable
USE $(MYDATABASE);
SELECT * FROM [dbo].[refresh_indexes]
GO
--Use again after a GO
SELECT * from $(MYDATABASE).[dbo].[refresh_indexes];
GO
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If you are using SQL Server you can setup global variables for entire scripts like:

:setvar sourceDB "lalalallalal"

and use later in script as: 

$(sourceDB)

Make sure SQLCMD mode is on in Server Managment Studi, you can do that via top menu Click Query and toggle SQLCMD Mode on.

More on topic can be found here: MS Documentation

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Temp tables are retained over GO statements, so...

SELECT 'value1' as variable1, 'mydatabasename' as DbName INTO #TMP


-- get a variable from the temp table
DECLARE @dbName VARCHAR(10) = (select top 1 #TMP.DbName from #TMP)
EXEC ('USE ' + @dbName)
GO


-- get another variable from the temp table
DECLARE @value1 VARCHAR(10) = (select top 1 #TMP.variable1 from #TMP)


DROP TABLE #TMP

It's not pretty, but it works

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Create your own stored procedures which save/load to a temporary table.

MyVariableSave   -- Saves variable to temporary table.
MyVariableLoad   -- Loads variable from temporary table.

Then you can use this:

print('Test stored procedures for load/save of variables across GO statements:')


declare @MyVariable int = 42
exec dbo.MyVariableSave @Name = 'test', @Value=@MyVariable
print('  - Set @MyVariable = ' + CAST(@MyVariable AS VARCHAR(100)))


print('  - GO statement resets all variables')
GO -- This resets all variables including @MyVariable


declare @MyVariable int
exec dbo.MyVariableLoad 'test', @MyVariable output
print('  - Get @MyVariable = ' + CAST(@MyVariable AS VARCHAR(100)))

Output:

Test stored procedures for load/save of variables across GO statements:
- Set @MyVariable = 42
- GO statement resets all variables
- Get @MyVariable = 42

You can also use these:

exec dbo.MyVariableList       -- Lists all variables in the temporary table.
exec dbo.MyVariableDeleteAll  -- Deletes all variables in the temporary table.

Output of exec dbo.MyVariableList:

Name    Value
test    42

It turns out that being able to list all of the variables in a table is actually quite useful. So even if you do not load a variable later, its great for debugging purposes to see everything in one place.

This uses a temporary table with a ## prefix, so it's just enough to survive a GO statement. It is intended to be used within a single script.

And the stored procedures:

-- Stored procedure to save a variable to a temp table.
CREATE OR ALTER PROCEDURE MyVariableSave
@Name varchar(255),
@Value varchar(MAX)
WITH EXECUTE AS CALLER
AS
BEGIN
SET NOCOUNT ON
IF NOT EXISTS (select TOP 1 * from tempdb.sys.objects where name = '##VariableLoadSave')
BEGIN
DROP TABLE IF EXISTS ##VariableLoadSave
CREATE TABLE ##VariableLoadSave
(
Name varchar(255),
Value varchar(MAX)
)
END
UPDATE ##VariableLoadSave SET Value=@Value WHERE Name=@Name
IF @@ROWCOUNT = 0
INSERT INTO ##VariableLoadSave SELECT @Name, @Value
END
GO
-- Stored procedure to load a variable from a temp table.
CREATE OR ALTER PROCEDURE MyVariableLoad
@Name varchar(255),
@Value varchar(MAX) OUT
WITH EXECUTE AS CALLER
AS
BEGIN
IF EXISTS (select TOP 1 * from tempdb.sys.objects where name = '##VariableLoadSave')
BEGIN
IF NOT EXISTS(SELECT TOP 1 * FROM ##VariableLoadSave WHERE Name=@Name)
BEGIN
declare @ErrorMessage1 as varchar(200) = 'Error: cannot find saved variable to load: ' + @Name
raiserror(@ErrorMessage1, 20, -1) with log
END


SELECT @Value=CAST(Value AS varchar(MAX)) FROM ##VariableLoadSave
WHERE Name=@Name
END
ELSE
BEGIN
declare @ErrorMessage2 as varchar(200) = 'Error: cannot find saved variable to load: ' + @Name
raiserror(@ErrorMessage2, 20, -1) with log
END
END
GO
-- Stored procedure to list all saved variables.
CREATE OR ALTER PROCEDURE MyVariableList
WITH EXECUTE AS CALLER
AS
BEGIN
IF EXISTS (select TOP 1 * from tempdb.sys.objects where name = '##VariableLoadSave')
BEGIN
SELECT * FROM ##VariableLoadSave
ORDER BY Name
END
END
GO
-- Stored procedure to delete all saved variables.
CREATE OR ALTER PROCEDURE MyVariableDeleteAll
WITH EXECUTE AS CALLER
AS
BEGIN
DROP TABLE IF EXISTS ##VariableLoadSave
CREATE TABLE ##VariableLoadSave
(
Name varchar(255),
Value varchar(MAX)
)
END
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If you just need a binary yes/no (like if a column exists) then you can use SET NOEXEC ON to disable execution of statements. SET NOEXEC ON works across GO (across batches). But remember to turn EXEC back on with SET NOEXEC OFF at the end of the script.

IF COL_LENGTH('StuffTable', 'EnableGA') IS NOT NULL
SET NOEXEC ON -- script will not do anything when column already exists


ALTER TABLE dbo.StuffTable ADD EnableGA BIT NOT NULL CONSTRAINT DF_StuffTable_EnableGA DEFAULT(0)
ALTER TABLE dbo.StuffTable SET (LOCK_ESCALATION = TABLE)
GO
UPDATE dbo.StuffTable SET EnableGA = 1 WHERE StuffUrl IS NOT NULL
GO
SET NOEXEC OFF

This compiles statements but does not execute them. So you'll still get "compile errors" if you reference schema that doesn't exist. So it works to "turn off" the script 2nd run (what I'm doing), but does not work to turn off parts of the script on 1st run, because you'll still get compile errors if referencing columns or tables that don't exist yet.

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You can make use of NOEXEC follow he steps below:

Create table

#temp_procedure_version(procedure_version varchar(5),pointer varchar(20))

insert procedure versions and pointer to the version into a temp table #temp_procedure_version

--example procedure_version pointer

insert into temp_procedure_version values(1.0,'first version')

insert into temp_procedure_version values(2.0,'final version')

then retrieve the procedure version, you can use where condition as in the following statement

Select @ProcedureVersion=ProcedureVersion from #temp_procedure_version where pointer='first version'

IF (@ProcedureVersion='1.0')
BEGIN
SET NOEXEC OFF  --code execution on
END
ELSE
BEGIN
SET NOEXEC ON  --code execution off
END

--insert procedure version 1.0 here

Create procedure version 1.0 as.....

SET NOEXEC OFF -- execution is ON

Select @ProcedureVersion=ProcedureVersion from #temp_procedure_version where pointer='final version'

IF (@ProcedureVersion='2.0')
BEGIN
SET NOEXEC OFF  --code execution on
END
ELSE
BEGIN
SET NOEXEC ON  --code execution off
END

Create procedure version 2.0 as.....

SET NOEXEC OFF -- execution is ON

--drop the temp table

Drop table #temp_procedure_version


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