MSSQL merge with distributed transaction alternative - sql

Question

I have a distributed transaction where I need to merge into the target remote table.
Now MERGE INTO isn't allowed according to MSDN: “target_table cannot be a remote table”.
So my workaround goes as follows: 0. begin distributed transaction 1. define a cursor 2. open it 3. if cursor has at least one record (CURSOR_STATUS()=1) fetch next 4. if exists (select top 1 * from target_remote_table where id = #myCurrentCursorId) -> when true update target_remote_table when false insert into target_remote_table 5. commit/rollback distributed transaction depending on trancount and xact_state
It works but I know that cursors are evil and you shouldn't use them. So I want to ask if there is any other way I could solve this by not using cursors?
USE [My_DB]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE PROCEDURE [dbo].[my_proc_merge_into_remote_table]
#ID_A INT,
#ID_B INT
AS
BEGIN
SET NOCOUNT ON;
-- CURSOR VALUES
DECLARE #field_A INT
DECLARE #field_B INT
DECLARE #field_C INT
DECLARE #field_D BIT
DECLARE #field_E INT
DECLARE #field_F DATETIME
DECLARE #field_G VARCHAR(20)
DECLARE #field_H DATETIME
DECLARE #field_I VARCHAR(20)
BEGIN TRY
BEGIN DISTRIBUTED TRANSACTION
-- CURSOR !!
DECLARE my_cursor CURSOR FOR
SELECT b.field_A ,
b.field_B,
c.field_C,
a.field_D,
a.field_E,
GETDATE() AS field_F,
a.field_G,
GETDATE() AS field_H,
a.field_I
FROM dbo.source_tbl a
LEFT JOIN dbo.base_element_tbl l
ON a.obj_id = l.obj_id AND a.element_id = l.element_id
INNER JOIN dbo.base_obj_tbl b
ON a.obj_id = b.obj_id
INNER JOIN dbo.element_tbl c
ON a.element_id = c.element_id
WHERE a.ID_B = #ID_B
AND a.ID_A = #ID_A;
OPEN my_cursor;
-- check if cursor result set has at least one row
IF CURSOR_STATUS('global', 'my_cursor') = 1 BEGIN
FETCH NEXT FROM my_cursor
INTO #field_A,
#field_B,
#field_C,
#field_D,
#field_E,
#field_F,
#field_G,
#field_H,
#field_I;
WHILE ##FETCH_STATUS = 0 BEGIN
-- HINT: MY_REMOTE_TARGET_TABLE is a Synonym which already points to the correct database and table
IF EXISTS(SELECT TOP 1 * FROM MY_REMOTE_TARGET_TABLE WHERE field_A = #field_A AND field_B = #field_B AND field_C = #field_C AND field_E = #field_E)
UPDATE MY_REMOTE_TARGET_TABLE SET field_D = #field_D, field_H = #field_H, field_I = #field_I;
ELSE
INSERT INTO MY_REMOTE_TARGET_TABLE (field_A, field_B, field_C, field_D, field_E, field_F, field_G, field_H, field_I) VALUES (#field_A, #field_B, #field_C, #field_D, #field_E, #field_F, #field_G, #field_H, #field_I);
FETCH NEXT FROM my_cursor
INTO #field_A,
#field_B,
#field_C,
#field_D,
#field_E,
#field_F,
#field_G,
#field_H,
#field_I;
END;
END;
CLOSE my_cursor;
DEALLOCATE my_cursor;
IF (##TRANCOUNT > 0 AND XACT_STATE() = 1)
BEGIN
COMMIT TRANSACTION
END
END TRY
BEGIN CATCH
IF (##TRANCOUNT > 0 AND XACT_STATE() = -1)
ROLLBACK TRANSACTION
END CATCH;
END

Answer 1

Here you go, first inner join target and source to update, then left join to insert missing.
;WITH CTE_Source AS
(
SELECT b.field_A ,
b.field_B,
c.field_C,
a.field_D,
a.field_E,
GETDATE() AS field_F,
a.field_G,
GETDATE() AS field_H,
a.field_I
FROM dbo.source_tbl a
LEFT JOIN dbo.base_element_tbl l
ON a.obj_id = l.obj_id AND a.element_id = l.element_id
INNER JOIN dbo.base_obj_tbl b
ON a.obj_id = b.obj_id
INNER JOIN dbo.element_tbl c
ON a.element_id = c.element_id
WHERE a.ID_B = #ID_B
AND a.ID_A = #ID_A;
)
UPDATE trgt
SET trgt.field_D = src.field_D, trgt.field_H = src.field_H, trgt.field_I = src.field_I
FROM MY_REMOTE_TARGET_TABLE trgt
INNER JOIN CTE_Source src ON src.field_A = trgt.field_A AND src.field_B = trgt.field_B AND src.field_C = trgt.field_C AND src.field_E = trgt.field_E
;WITH CTE_Source AS
(
SELECT b.field_A ,
b.field_B,
c.field_C,
a.field_D,
a.field_E,
GETDATE() AS field_F,
a.field_G,
GETDATE() AS field_H,
a.field_I
FROM dbo.source_tbl a
LEFT JOIN dbo.base_element_tbl l
ON a.obj_id = l.obj_id AND a.element_id = l.element_id
INNER JOIN dbo.base_obj_tbl b
ON a.obj_id = b.obj_id
INNER JOIN dbo.element_tbl c
ON a.element_id = c.element_id
WHERE a.ID_B = #ID_B
AND a.ID_A = #ID_A;
)
INSERT INTO MY_REMOTE_TARGET_TABLE (field_A, field_B, field_C, field_D, field_E, field_F, field_G, field_H, field_I)
SELECT field_A, field_B, field_C, field_D, field_E, field_F, field_G, field_H, field_I
FROM CTE_Soure src
LEFT JOIN MY_REMOTE_TARGET_TABLE trgt ON src.field_A = trgt.field_A AND src.field_B = trgt.field_B AND src.field_C = trgt.field_C AND src.field_E = trgt.field_E
WHERE trgt.field_A IS NULL