MERGE
Introduction#
Starting with SQL Server 2008, it is possible to perform insert, update, or delete operations in a single statement using the MERGE statement.
The MERGE statement allows you to join a data source with a target table or view, and then perform multiple actions against the target based on the results of that join.
Syntax#
- As per MSDN - https://msdn.microsoft.com/en-us/library/bb510625.aspx
[ WITH <common_table_expression> [,…n] ] MERGE [ TOP ( expression )
[ PERCENT ] ] [ INTO ] <target_table> [ WITH ( <merge_hint> ) ] [ [
AS ] table_alias ] USING <table_source> ON <merge_search_condition> [
WHEN MATCHED [ AND <clause_search_condition> ] THEN <merge_matched> ]
[ …n ] [ WHEN NOT MATCHED [ BY TARGET ] [ AND
<clause_search_condition> ] THEN <merge_not_matched> ] [ WHEN NOT
MATCHED BY SOURCE [ AND <clause_search_condition> ] THEN
<merge_matched> ] [ …n ] [ <output_clause> ] [ OPTION (
<query_hint> [ ,…n ] ) ] ; <target_table> ::= { [ database_name .
schema_name . | schema_name . ] target_table } <merge_hint>::= { { [
<table_hint_limited> [ ,…n ] ] [ [ , ] INDEX ( index_val [ ,…n ]
) ] } } <table_source> ::= { table_or_view_name [ [ AS ] table_alias
] [ <tablesample_clause> ] [ WITH ( table_hint [ [ , ]…n ] ) ] |
rowset_function [ [ AS ] table_alias ] [ ( bulk_column_alias [ ,…n
] ) ] | user_defined_function [ [ AS ] table_alias ] | OPENXML
<openxml_clause> | derived_table [ AS ] table_alias [ ( column_alias
[ ,…n ] ) ] | <joined_table> | <pivoted_table> | <unpivoted_table>
} <merge_search_condition> ::= <search_condition> <merge_matched>::=
{ UPDATE SET <set_clause> | DELETE } <set_clause>::= SET {
column_name = { expression | DEFAULT | NULL } | { udt_column_name.{ {
property_name = expression | field_name = expression } | method_name
( argument [ ,…n ] ) } } | column_name { .WRITE ( expression ,
@Offset , @Length ) } | @variable = expression | @variable = column =
expression | column_name { += | -= | *= | /= | %= | &= | ^= | |= }
expression | @variable { += | -= | *= | /= | %= | &= | ^= | |= }
expression | @variable = column { += | -= | *= | /= | %= | &= | ^= |
|= } expression } [ ,…n ] <merge_not_matched>::= { INSERT [ (
column_list ) ] { VALUES ( values_list ) | DEFAULT VALUES } }
<clause_search_condition> ::= <search_condition> ::= { [ NOT ] | (
<search_condition> ) } [ { AND | OR } [ NOT ] { | (
<search_condition> ) } ] [ ,…n ] ::= { expression { = | < > | ! = |
| > = | ! > | < | < = | ! < } expression | string_expression [ NOT ] LIKE string_expression [ ESCAPE ‘escape_character’ ] | expression [
| > = | ! > | < | < = | ! < } { ALL | SOME | ANY} ( subquery ) | EXISTS ( subquery ) } <output_clause>::= { [ OUTPUT <dml_select_list>
Remarks#
Performs insert, update, or delete operations on a target table based on the results of a join with a source table. For example, you can synchronize two tables by inserting, updating, or deleting rows in one table based on differences found in the other table.
MERGE to Insert / Update / Delete
MERGE INTO targetTable
USING sourceTable
ON (targetTable.PKID = sourceTable.PKID)
WHEN MATCHED AND (targetTable.PKID > 100) THEN
DELETE
WHEN MATCHED AND (targetTable.PKID <= 100) THEN
UPDATE SET
targetTable.ColumnA = sourceTable.ColumnA,
targetTable.ColumnB = sourceTable.ColumnB
WHEN NOT MATCHED THEN
INSERT (ColumnA, ColumnB) VALUES (sourceTable.ColumnA, sourceTable.ColumnB);
WHEN NOT MATCHED BY SOURCE THEN
DELETE
; --< Required
Description:
MERGE INTO targetTable
- table to be modifiedUSING sourceTable
- source of data (can be table or view or table valued function)ON ...
- join condition betweentargetTable
andsourceTable
.WHEN MATCHED
- actions to take when a match is found-
AND (targetTable.PKID > 100)
- additional condition(s) that must be satisfied in order for the action to be taken
THEN DELETE
- delete matched record from thetargetTable
THEN UPDATE
- update columns of matched record specified bySET ....
WHEN NOT MATCHED
- actions to take when match is not found intargetTable
WHEN NOT MATCHED BY SOURCE
- actions to take when match is not found insourceTable
Comments:
If a specific action is not needed then omit the condition e.g. removing WHEN NOT MATCHED THEN INSERT
will prevent records from being inserted
Merge statement requires a terminating semicolon.
Restrictions:
WHEN MATCHED
does not allowINSERT
actionUPDATE
action can update a row only once. This implies that the join condition must produce unique matches.
Merge Using CTE Source
WITH SourceTableCTE AS
(
SELECT * FROM SourceTable
)
MERGE
TargetTable AS target
USING SourceTableCTE AS source
ON (target.PKID = source.PKID)
WHEN MATCHED THEN
UPDATE SET target.ColumnA = source.ColumnA
WHEN NOT MATCHED THEN
INSERT (ColumnA) VALUES (Source.ColumnA);
MERGE using Derived Source Table
MERGE INTO TargetTable AS Target
USING (VALUES (1,'Value1'), (2, 'Value2'), (3,'Value3'))
AS Source (PKID, ColumnA)
ON Target.PKID = Source.PKID
WHEN MATCHED THEN
UPDATE SET target.ColumnA= source.ColumnA
WHEN NOT MATCHED THEN
INSERT (PKID, ColumnA) VALUES (Source.PKID, Source.ColumnA);
Merge Example - Synchronize Source And Target Table
To Illustrate the MERGE Statement, consider the following two tables -
-
dbo.Product : This table contains information about the product that company is currently selling
-
dbo.ProductNew: This table contains information about the product that the company will sell in the future.
The following T-SQL will create and populate these two tables
IF OBJECT_id(N'dbo.Product',N'U') IS NOT NULL
DROP TABLE dbo.Product
GO
CREATE TABLE dbo.Product (
ProductID INT PRIMARY KEY,
ProductName NVARCHAR(64),
PRICE MONEY
)
IF OBJECT_id(N'dbo.ProductNew',N'U') IS NOT NULL
DROP TABLE dbo.ProductNew
GO
CREATE TABLE dbo.ProductNew (
ProductID INT PRIMARY KEY,
ProductName NVARCHAR(64),
PRICE MONEY
)
INSERT INTO dbo.Product VALUES(1,'IPod',300)
,(2,'IPhone',400)
,(3,'ChromeCast',100)
,(4,'raspberry pi',50)
INSERT INTO dbo.ProductNew VALUES(1,'Asus Notebook',300)
,(2,'Hp Notebook',400)
,(3,'Dell Notebook',100)
,(4,'raspberry pi',50)
Now, Suppose we want to synchoronize the dbo.Product Target Table with the dbo.ProductNew table. Here is the criterion for this task:
-
Product that exist in both the dbo.ProductNew source table and the dbo.Product target table are updated in the dbo.Product target table with new new Products.
-
Any product in the dbo.ProductNew source table that do not exist in the dob.Product target table are inserted into the dbo.Product target table.
-
Any Product in the dbo.Product target table that do not exist in the dbo.ProductNew source table must be deleted from the dbo.Product target table.
Here is the MERGE statement to perform this task.
MERGE dbo.Product AS SourceTbl
USING dbo.ProductNew AS TargetTbl ON (SourceTbl.ProductID = TargetTbl.ProductID)
WHEN MATCHED
AND SourceTbl.ProductName <> TargetTbl.ProductName
OR SourceTbl.Price <> TargetTbl.Price
THEN UPDATE SET SourceTbl.ProductName = TargetTbl.ProductName,
SourceTbl.Price = TargetTbl.Price
WHEN NOT MATCHED
THEN INSERT (ProductID, ProductName, Price)
VALUES (TargetTbl.ProductID, TargetTbl.ProductName, TargetTbl.Price)
WHEN NOT MATCHED BY SOURCE
THEN DELETE
OUTPUT $action, INSERTED.*, DELETED.*;
Note:Semicolon must be present in the end of MERGE statement.
Merge using EXCEPT
Use EXCEPT to prevent updates to unchanged records
MERGE TargetTable targ
USING SourceTable AS src
ON src.id = targ.id
WHEN MATCHED
AND EXISTS (
SELECT src.field
EXCEPT
SELECT targ.field
)
THEN
UPDATE
SET field = src.field
WHEN NOT MATCHED BY TARGET
THEN
INSERT (
id
,field
)
VALUES (
src.id
,src.field
)
WHEN NOT MATCHED BY SOURCE
THEN
DELETE;