Using multiple statements in WHEN MATCHED

问题

I am using MERGE statement in order to insert XML input to SQL Server database table. How to execute multiple conditions in WHEN MATCHED block. Please refer the below code.

USING TableRelationship AS new
  ON (new.TableRelationshipTypeID = old.TableRelationshipTypeID) AND old.ToRoleID = @RoleID

WHEN MATCHED THEN 
   UPDATE 
       SET old.FromRoleID = new.FromRoleID
   -- Condition 2
   -- Condition 3

Currently WHEN MATCHED it only executes this old.FromRoleID = new.FromRoleID line. How can I execute all 3 lines (-- Condition 2 and 3) inside WHEN NOT MATCHED condition.

Ex :

This is what I expect. WHEN MATCHED I just want to update the old field (old.ThruDate = GETDATE()) and insert a record to the same table. I cant separate those statements by a comma. SQL emits

Incorrect Syntax

MERGE INTO Party.TableRelationship AS old
USING TableRelationship AS new ON (new.TableRelationshipTypeID = old.TableRelationshipTypeID) AND old.ToRoleID = @RoleID

WHEN MATCHED THEN 
   UPDATE 
       SET old.ThruDate = GETDATE(),
   INSERT (FromRoleID, ToRoleID, TableRelationshipTypeID)
   VALUES (new.FromRoleID, new.ToRoleID, new.TableRelationshipTypeID);

Thank you.

回答1:

You could use INSERT over DML to achieve it:

INSERT INTO tab_name(FromRoleID, ToRoleID, TableRelationshipTypeID)
SELECT FromRoleID, ToRoleID, TableRelationshipTypeID
FROM (
  MERGE INTO Party.TableRelationship AS old
  USING TableRelationship AS new 
     ON new.TableRelationshipTypeID = old.TableRelationshipTypeID 
    AND old.ToRoleID = @RoleID
  WHEN MATCHED THEN 
    UPDATE SET old.ThruDate = GETDATE()
    OUTPUT $action, FromRoleID, ToRoleID, TableRelationshipTypeID
) sub(action, FromRoleID, ToRoleID, TableRelationshipTypeID)
WHERE action = 'UPDATE';

Keep in mind that this method has some limitations more info: MS Connect

回答2:

This isn't what a merge statement is for. A merge statement either updates records if they already exist (WHEN MATCHED THEN), or it inserts records if they don't exist (WHEN NOT MATCHED THEN). It's not designed to insert records upon finding a match

(Side note: sqlserver merge statements can specify WHEN MATCHED twice, perhaps you'd use this with the aim that one of the matchings deletes records from the target that match some additional criteria, and the other specifies a list of columns to update if the additional logical test is false)

If you want to mix and match your inserting and updating when a record is matched, you'll need to use something else like a stored procedure or trigger that reacts to the update

Alternatively if you're just asking about how syntax of a merge statement, your insert directives need to be preceded by WHEN NOT MATCHED THEN INSERT ...

回答3:

You cannot do that - it is just plain not supported by SQL Server's MERGE statement.

In the WHEN MATCHED case, you can only do one UPDATE (or DELETE) statement - you cannot have multiple different statements after one another.

Check the official MSDN documentation for MERGE - it spells out what's possible and what's not supported in great detail:

Syntax:

MERGE   
    USING <table_source> ON <merge_search_condition>  
    [ WHEN MATCHED [ AND <clause_search_condition> ]  
        THEN <merge_matched> ] [ ...n ]  
;  

<merge_matched>::=  
    { UPDATE SET <set_clause> | DELETE }  

The MERGE statement can have at most two WHEN MATCHED clauses. If two clauses are specified, then the first clause must be accompanied by an AND clause. For any given row, the second WHEN MATCHED clause is only applied if the first is not. If there are two WHEN MATCHED clauses, then one must specify an UPDATE action and one must specify a DELETE action

回答4:

Those are not conditions, they are assignment clauses. You separate them by commas, as in update:

USING TableRelationship AS new
  ON (new.TableRelationshipTypeID = old.TableRelationshipTypeID) AND 
     old.ToRoleID = @RoleID
  WHEN MATCHED THEN UPDATE
      SET old.FromRoleID = new.FromRoleID,
          <assignment 2>,
          <assignment 3>;

来源：https://stackoverflow.com/questions/46141142/using-multiple-statements-in-when-matched