To do multiple DML operations in SQL SERVER we use MERGE, that a strong feature of SQL SERVER, In earlier versions of SQL SERVER we had to write separate
statement for INSERT, UPDATE, DELETE, now by using MERGE we can perform INSERT, UPDATE, DELETE in one statement
by checking data, if data matched then update otherwise insert or in particular condition we can
also delete.
Note-Merge statement read entire data and processed only
one.
The Merge query is given below:
Suppose there are two tables, Table1 and table2, table1
contains data about books like ISBN, Title, quantity, price, etc.. and table2
contains updated data of book so here we need to update Table1 from Table2,
Table may have new records or updated records(like quantity, price etc ) or it may
be some records should be delete from Table1.
CREATE TABLE TABLE1
(
biBookId BIGINT IDENTITY(1,1),
vIsbn VARCHAR(20),
iQty INT,
dcPrice DECIMAL(18,2)
)
CREATE TABLE TABLE2
(
biBookId BIGINT IDENTITY(1,1),
vIsbn VARCHAR(20),
iQty INT,
dcPrice DECIMAL(18,2)
)
/*insert some
data in table1*/
INSERT INTO TABLE1(vIsbn,iQty,dcPrice) VALUES('9987876543343',10,0.00)
INSERT INTO TABLE1(vIsbn,iQty,dcPrice) VALUES('8898576476532',1,21.30)
INSERT INTO TABLE1(vIsbn,iQty,dcPrice) VALUES('9898765456763',50,4.00)
INSERT INTO TABLE1(vIsbn,iQty,dcPrice) VALUES('8987655663452',0,5.00)
/*insert some
data in table2*/
INSERT INTO TABLE2(vIsbn,iQty,dcPrice) VALUES('9987876543343',20,0.00)
INSERT INTO TABLE2(vIsbn,iQty,dcPrice) VALUES('8898576476532',1,31.30)
INSERT INTO TABLE2(vIsbn,iQty,dcPrice) VALUES('9898765456763',5,4.00)
INSERT INTO TABLE2(vIsbn,iQty,dcPrice) VALUES('8987655663452',0,15.00)
INSERT INTO TABLE2(vIsbn,iQty,dcPrice) VALUES('8987655663451',11,25.00)
/*data in table1
before merge*/
select * from TABLE1
/*MERGE
statement*/
MERGE TABLE1 AS tbl1
USING (SELECT vIsbn,iQty,dcPrice FROM TABLE2) as tbl2
ON tbl1.vIsbn=tbl2.vIsbn
WHEN MATCHED AND tbl2.iQty=0 THEN DELETE
WHEN MATCHED THEN UPDATE
SET tbl1.iQty=tbl2.iQty,
tbl1.dcPrice=tbl2.dcPrice
WHEN NOT MATCHED THEN
INSERT(vIsbn,iQty,dcPrice)
VALUES(tbl2.vIsbn, tbl2.iQty, tbl2.dcPrice);
GO
SELECT * FROM TABLE1
DROP TABLE TABLE1
DROP TABLE TABLE2
Hi Dilip,
ReplyDeleteOn duplicate records Merge is failed, any idea to prevent it.