How to use BEGIN TRANSACTION with while loop in SQL Server? - sql-server

Question

How to use BEGIN TRANSACTION with while loop in SQL Server?
This query never finishes perhaps because it stops and look for COMMIT TRANSACTION after inserting one row (when #cnt = 1) but I don't want to COMMIT TRANSACTION because I want to see results before committing.
BEGIN TRANSACTION
DECLARE #cnt INT = 0;
WHILE #cnt <= 100
BEGIN
DECLARE #offset INT = 1
INSERT INTO totalSales (col1, col2)
SELECT
'Col1', ROW_NUMBER() OVER (ORDER BY col2) + #offset
FROM
sales
SET #cnt = #cnt + 1;
END;
So how I can check result before commit in while loop?

Answer 1

You should create a BEGIN TRAN outer (general), and inside loop while create a BEGIN TRAN inner (with a trans name).
Inside loop, if are conditions to rollbacks only for this iteration i use SAVE TRAN savepoint for not lose previous trans.
I 've created an example tests in loop while with conditional inserts and rollback savepoint:
declare #num int
set #num = 0
--drop table #test
create table #test (
valor Varchar(100)
)
begin tran
while #num <= 5
begin
begin transaction tran_inner
insert into #test (valor) values ('INSERT 1 INNER -> ' + convert(varchar(10),#num))
save transaction sv_inner
insert into #test (valor) values ('INSERT 2 EVEN - SAVEPOINT -> ' + convert(varchar(10),#num))
if #num % 2 = 0 begin
commit transaction sv_inner
end else begin
rollback transaction sv_inner
end
insert into #test (valor) values ('INSERT 3 INNER -> ' + convert(varchar(10),#num))
set #num = #num + 1
if ##trancount > 0 begin
commit transaction tran_inner
end
end
select valor from #test;
if ##trancount > 0 begin
commit tran
end
Return rows: 1, 2 if iteration even, and 3.

Answer 2

In the same batch (within the same transaction) you can simply issue a SELECT command to see the updated content of the table. Changes will be persisted when the COMMIT TRANSACTION statement is executed or reverted on ROLLBACK.
CREATE TABLE test (id INT IDENTITY(1,1), x VARCHAR(32));
GO
BEGIN TRANSACTION;
INSERT INTO test (x) VALUES ('a');
INSERT INTO test (x) VALUES ('b');
SELECT * FROM test;
ROLLBACK TRANSACTION;
Example: http://sqlfiddle.com/#!6/e4910/2
Alternatively you can use the INSERT INTO .. OUTPUT construct to output the result of the INSERT statement.
Docs: https://learn.microsoft.com/en-us/sql/t-sql/queries/output-clause-transact-sql
Outside the batch (using a second connection), you can use READ UNCOMMITTED isolation level to be able to read records not committed yet.
Docs: https://technet.microsoft.com/en-us/library/ms189122(v=sql.105).aspx

Answer 3

If you are saying it never finishes it sounds to me like you are getting some blocking going on because that loop runs just fine.
https://www.mssqltips.com/sqlservertip/2429/how-to-identify-blocking-in-sql-server/
I HIGHLY recommend using Adam Machanic's sp_WhoIsActive for this as well: http://whoisactive.com