Scope of GOTO with GO

The GOTO statement is used to break the normal flow of execution to a particular label specified with GOTO statement. We will see this with examples, but the question of matter is whether GOTO statement goes/switch beyond the block defined with GO statement.  

Lets checkout with an example, here we are checking a condition in “if statement”, if the condition evaluates to true then we are instructing normal flow to break and go to a particular point i.e. VKM_POINT, but in this example we define the label VKM_POINT outside the GO block, now let’s see whether the GOTO has scope beyond the block where it is used.      

declare @tempVar int

set @tempVar = 10

if @tempVar =10

      goto VKM_POINT

go

VKM_POINT:

      print 'Honey I was waiting for you'

Msg 133, Level 15, State 1, Line 5

A GOTO statement references the label 'VKM_POINT' but the label has not been declared.

So with the output we saw that GOTO is unable to switch the flow beyond the scope of batch. Lets modify the same example to have label point (VKM_POINT) inside the batch.

declare @tempVar int

set @tempVar = 10

if @tempVar =10

      goto VKM_POINT

VKM_POINT:

      print 'Honey I was waiting for you'

go

Honey I was waiting for you

Here with the output we can see that GOTO works properly when it has to jump to point which is inside the block where GOTO is used.

Conclusion: GOTO has scope only within a block

When programmer carry out rules, the ordinary human race slight.. J

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Variable Scope and CONTEXT_INFO

In SQL Server the variable which we declare in the block has scope to that block only, when you try to access that variable outside that scope, you won’t be able to access it. Let see with an example

Here we are creating two blocks, in first block we are declaring a variable @tempInt of INT type and initializing it with 5. And in second block, we are just trying to print the value of that variable.

declare @tempInt int

set @tempInt = 5

print @tempInt

go --Here we finished our first block

print @tempInt

go --Here we finished our Second block

5

Msg 137, Level 15, State 2, Line 1

Must declare the scalar variable "@tempInt".

From the output we can see the first Print which is present in first block where the variable was declared and initialized display its value but which we try to display the value of variable in second block it fires error saying, declare variable “@tempInt.

Conclusion: The scope of variable exists only to the block where it gets declared.

This problem can be solved using CONTEXT_INFO, context_info is a variable specific to a session of type varbinary(128), to access the value of context_info we have a function context_info(). You can also set your own value in context_info variable.

Session variable storing Varchar value

declare @strSource varbinary(50)

select @strSource = convert(varbinary(50),'My testing')

set context_info @strSource

declare @strDesti varchar(50)

select @strDesti =  cast(cast(context_info() as binary(50)) as varchar)

print @strDesti       

My testing

Session variable storing int value

declare @strSourceInt varbinary(50)

select @strSourceInt = convert(varbinary(max),387)

set context_info @strSourceInt

declare @strDestiInt int

select @strDestiInt = cast(cast(context_info() as binary(4)) as int)

print @strDestiInt

387

Session Variable scope

declare @strDesti varchar(50)

select @strDesti =  cast(cast(context_info() as binary(50)) as varchar)

print @strDesti       

declare @strSourceInt varbinary(50)

select @strSourceInt = convert(varbinary(max),300)

set context_info @strSourceInt

declare @strDestiInt int

select @strDestiInt = cast(cast(context_info() as binary(4)) as int)

print cast(@strDestiInt as varchar) + ' from Ist Batch'

go      --Here we finished first block

print cast(cast(cast(context_info() as binary(4)) as int) as varchar) + ' from IInd Batch'

declare @strSourceInt varbinary(50)

select @strSourceInt = convert(varbinary(max),400)

set context_info @strSourceInt

declare @strDestiInt int

select @strDestiInt = cast(cast(context_info() as binary(4)) as int)

print cast(@strDestiInt as varchar) + ' New value from IIst Batch'

go    --Here we finished second block

print cast(cast(cast(context_info() as binary(4)) as int) as varchar) + ' from IIIrd Batch'

go    --Here we finished third block

300 from Ist Batch

300 from IInd Batch

400 New value from IIst Batch

400 from IIIrd Batch

So from the output we can see that the first value which gets assigned to context_info variable was 300 and it is also accessable in second block too as we saw in second line of output then we modified the value of context_info variable in third block to 400, and again in third block we can access the modified value of context_info.

Conclusion: CONTEXT_INFO retains its value across blocks and u can also set new value to context info in any block.

When programmer do code, nothing annoys them so much.. J

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GO, you can also specify your own word as a batch terminator

GO is a batch terminator, you can however change it to whatever you want.

Also read previous articles on GO

GO and the Stored Procedure

GO, is it a SQL command, a jump to pointer or what exactly?

GO and the Scope of variable.

Go to Tool-> Option -> Query Execution

And then change the Batch Separator to word of your choice, here in this example, I changed it to BATCH.

Now if I try to write code with batch separators GO, SSMS will not recognize.

alter table tab2

add  d_manager varchar(10)

GO

select d_id,d_name,d_manager from tab2

Msg 102, Level 15, State 1, Line 4

Incorrect syntax near 'GO'.

Now if we replace GO with BATCH, it should work properly. Lets see

alter table tab2

add  d_manager varchar(10)

BATCH

select d_id,d_name,d_manager from tab2 

So this is how you can specify your own word as a batch terminator

Your code, sound the horn 

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GO and batch execution multiple times.

Go is a useful command especially when you want to execute a batch multiple times. For time being we can take an example of inserting multiple dummy records in a table, with just ONE insert statement. Also read previous articles on GO

GO and the Stored Procedure

GO, is it a SQL command, a jump to pointer or what exactly?

GO and the Scope of variable.

Let’s create a temporary table for this purpose.

use testDemo

go --First Batch

create table #tempTable

(tempID uniqueidentifier,

tempMonth int,

tempDateTime datetime )

GO -- Second Batch

Command(s) completed successfully.

These batches will just execute these separate batches for once as default value for GO is one. Lets insert 100 records in our temporary table with just one insert statement

insert into #tempTable (tempID, tempMonth, tempDateTime)

select NEWID(),(CAST(100000*RAND() AS INT) % 12) + 1 ,GETDATE()

GO 10

Batch execution completed 10 times.

“Go 100” will execute this insertion batch for ten times, and exultantly 10 records will be inserted. That’s what I call it “Power of GO”. Check this.

select * from #tempTable

tempID                               tempMonth   tempDateTime

------------------------------------ ----------- -----------------------

C2055F4A-0FF9-4A2C-BB9F-9CC665EEC009 3           2013-03-25 14:30:37.830

4322FE78-4494-45B3-8923-5D9CD5F030CA 3           2013-03-25 14:30:37.933

86D89223-530B-423E-AAB1-8E65601D821B 8           2013-03-25 14:30:37.933

7E1A8812-9A8E-412D-8EE4-4FBE02FB4CBB 8           2013-03-25 14:30:37.937

917C89A6-1DFB-4375-A6E3-5C15F556AFCB 6           2013-03-25 14:30:37.940

7DEBDD5D-E2B9-45BB-9D65-D911DA32F431 7           2013-03-25 14:30:37.940

CC124777-7AE4-47A8-B7CA-0EE566D01465 5           2013-03-25 14:30:37.940

6A0E6F7C-47A6-4F2A-A8C0-58E4A0B498E2 4           2013-03-25 14:30:37.947

CB22E285-689A-466A-A7EB-E0734ED1435B 3           2013-03-25 14:30:37.950

7102D516-03AC-4EE9-93C8-820477E645D6 5           2013-03-25 14:30:37.953

(10 row(s) affected)

Now drop the temporary table

drop table #tempTable

Conclusion: GO can be used for multiple times batch execution.

Honk if you hate coding

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GO and the Stored Procedure

In this article, we will see how GO can have an effect on writing stored procedure, before that go through my previous post 

GO, is it a SQL command, a jump to pointer or what exactly?

GO and the Scope of variable.

We will directly jump into the example to see the effect of go in stored procedure, Now we are creating the stored procedure MyManager, and if you notice after end block of stored procedure, there is a select statement and a GO statement proceed with it.

Create procedure MyManager

as

begin

     select 'My Manager is the best one.'

end

select 'Oh come on! This is absolutly lie'

go

Command(s) completed successfully.

Now if we try to execute the procedure..

exec MyManager

---------------------------

My Manager is the best one.

(1 row(s) affected)

---------------------------------

Oh come on! This is absolutly lie

(1 row(s) affected)

Say, if you show this stored procedure’s output to your Manager, you better have a new job lined up.

What happened? You intended to show him only the first line, but the output of the second select also is displayed.

Why? Because the whole code is scripted into the syscomments table until a GO command is found.

Now lets drop the procedure and recreate the same

drop proc MyManager

Command(s) completed successfully.

Procedure lets recreate the same procedure, where select statement appears after the GO statement.

Create procedure MyManager

as

begin

     select 'My Manager is the best one.'

end

go

select 'Oh come on! This is absolutly lie'

Now if we execute the procedure, we gets our desired result.

exec MyManager

---------------------------

My Manager is the best one.

(1 row(s) affected)

Conclusion: If the stored procedure isn’t immediately followed by a GO command, an executable statement that appears after the stored procedure will be executed together with the stored procedure, which as we have seen can have unintended consequences.

I just like to code and be happy.

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GO and the Scope of variable.

We  will be see the scope of a local variable and it affect with the GO statement, before that go through my previous post  GO, is it a SQL command, a jump to pointer or what exactly?

At the present let’s discuss about the scope of a local variable, by execute the following set of t-SQL statements

declare @strMsg varchar(25)

set @strMsg = 'Testing scope with go'

select @strMsg as GoMessage

GoMessage

-------------------------

Testing scope with go

(1 row(s) affected)

We can see, it executed properly and the value of the local variable @strMsg which was set, displays accurately with select statement.  

Now let’s add GO statement in between set and select statement and see the result. Will it make any difference let’s see

declare @strMsg varchar(25)

set @strMsg = 'Testing scope with go'

go

select @strMsg as GoMessage

Msg 137, Level 15, State 2, Line 1

Must declare the scalar variable "@strMsg".

Here to our shock we found error saying @strMsg not declared… :-O, How come, we have already declare and set @strMsg before displaying it, then what is the problem?

Reason: Encounter of GO statement  send signal to to Sql Server instance so to send the current batch  (T-SQL statements between  GO commands)  and execute Independently.

This means, the satement before go will form a batch and execute independently and the statement after go to the next encounter go will form the next batch and executes seperatly.

In our example, 2 batches gets created and executes seperately

First batch is this, which executes independently

declare @strMsg varchar(25)

set @strMsg = 'Testing scope with go'

where as, Second batch is this, which ssms sent as a independent execution.

select @strMsg as GoMessage

So due to independent execution of second batch, it throws error, because we are querying a string value, without declaring it.

Wrapping up : GO is not a Transact-SQL statement; it’s just a command to send signal so to send the current batch  (T-SQL statements between two GO commands) of T-SQL statements to Sql Server instance.

A fair code ought to be pursued by the deed in silence.

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GO, is it a SQL command, a jump to pointer or what exactly?

Yesterday it happened one of my very good friend asked me, why it is necessary to write go statement in an arrangement like this

alter table tblPopulation

add street varchar(10) 

go

select country,state,street,population from tblPopulation

Let’s find out what the picture behind GO statement.

To understated this lets first execute the same statement without having GO in between the alter and select statement.

alter table tblPopulation

add street varchar(10)

select country,state,street,population from tblPopulation

Msg 207, Level 16, State 1, Line 4

Invalid column name 'street'.

Msg 207, Level 16, State 1, Line 4

Invalid column name 'population'.

From the error message it is clear that the new field which we are adding to the existing table tblPopulation has not been added yet and the SQL parser parse the select command, due to which it didn’t find the new coloum population and throws a error.

Where as if we add go in between select and alter statement, we will be able to execute the statement with all ease.  

alter table tblPopulation

add street varchar(10)

go

select country,state,street from tblPopulation

country state     street

----------------------------

India   Delhi     NULL

India   Delhi     NULL

India   Delhi     NULL

India   Karnataka NULL

(4 row(s) affected)

This shows, If you put a GO between the two statements, it'll work, because SSMS won't parse and verify the whole statement ahead of time - it will do the first part, and then only parse the second (after the GO).

LEARNING: They're not strictly required - they're just instructions for the SQL Server Management Studio to execute the statements up to this point now and then keep on going. GO is not a T-SQL keyword or anything - it's just an instruction that works in SSMS.

Conclusion: Sometimes, you need a GO - e.g. if you add a column to a table, and then want to select it again, you need to have a GO between the adding of the column, and the query of it.

Code it and live the moment to the utmost satisfaction

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