MERGE Transact SQL Microsoft Docs.THIS TOPIC APPLIES TO SQL Server starting with 2.Azure SQL Database.Azure SQL Data Warehouse Parallel Data Warehouse 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.Performance Tip The conditional behavior described for the MERGE statement works best when the two tables have a complex mixture of matching characteristics.For example, inserting a row if it does not exist, or updating the row if it does match.Query result cache in oracle 11g.Caching has been a feature of Oracle for as long as most of us can remember.Over the many years and versions, Oracle has.Screen-Shot-2012-08-22-at-2.02.11-PM.png' alt='Invalid Update Invalid Number Of Rows In Section 08' title='Invalid Update Invalid Number Of Rows In Section 08' />When simply updating one table based on the rows of another table, improved performance and scalability can be achieved with basic INSERT, UPDATE, and DELETE statements.For example INSERT tblA col, col.SELECT col, col. 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WHERE NOT EXISTS SELECT col FROM tblA A2 WHERE A2.B.Transact SQL Syntax Conventions.Syntax WITH lt commontableexpression.TOP expression PERCENT.INTO lt targettable WITH lt mergehint AS tablealias.USING lt tablesource.ON lt mergesearchcondition.WHEN MATCHED AND lt clausesearchcondition.THEN lt mergematched.WHEN NOT MATCHED BY TARGET AND lt clausesearchcondition.THEN lt mergenotmatched.WHEN NOT MATCHED BY SOURCE AND lt clausesearchcondition.THEN lt mergematched.OPTION lt queryhint.INDEX indexval.AS tablealias lt tablesampleclause.WITH tablehint ,.AS tablealias.AS tablealias.OPENXML lt openxmlclause.AS tablealias columnalias.UPDATE SET lt setclause DELETE.DEFAULT NULL.WRITE expression, Offset, Length.INSERT columnlist.VALUES valueslist.DEFAULT VALUES.NOT lt predicate lt searchcondition.AND OR NOT lt predicate lt searchcondition.NOT LIKE stringexpression.ESCAPE escapecharacter.NOT BETWEEN expression AND expression.IS NOT NULL.CONTAINS.FREETEXT column, freetextstring.NOT IN subquery expression.ALL SOME ANY subquery.EXISTS subquery.OUTPUT lt dmlselectlist INTO tablevariable outputtable.OUTPUT lt dmlselectlist.AS columnaliasidentifier.DELETED INSERTED fromtablename.Arguments WITH lt commontableexpression Specifies the temporary named result set or view, also known as common table expression, defined within the scope of the MERGE statement.The result set is derived from a simple query and is referenced by the MERGE statement.For more information, see WITH commontableexpression Transact SQL.TOP expression PERCENT Specifies the number or percentage of rows that are affected.The rows referenced in the TOP expression are not arranged in any order.For more information, see TOP Transact SQL.The TOP clause is applied after the entire source table and the entire target table are joined and the joined rows that do not qualify for an insert, update, or delete action are removed.The TOP clause further reduces the number of joined rows to the specified value and the insert, update, or delete actions are applied to the remaining joined rows in an unordered fashion.That is, there is no order in which the rows are distributed among the actions defined in the WHEN clauses.For example, specifying TOP 1.Because the MERGE statement performs a full table scan of both the source and target tables, IO performance can be affected when using the TOP clause to modify a large table by creating multiple batches.In this scenario, it is important to ensure that all successive batches target new rows.Is the name of the database in which targettable is located.Is the name of the schema to which targettable belongs.Is the table or view against which the data rows from lt tablesource are matched based on lt clausesearchcondition.Agile Software Development Life Cycle Ppt Slides '>Agile Software Development Life Cycle Ppt Slides .WHEN clauses of the MERGE statement.If targettable is a view, any actions against it must satisfy the conditions for updating views.For more information, see Modify Data Through a View.AS tablealias.Is an alternative name used to reference a table.USING lt tablesource Specifies the data source that is matched with the data rows in targettable based on lt mergesearch condition.The result of this match dictates the actions to take by the WHEN clauses of the MERGE statement.Transact SQL table value constructor to construct a table by specifying multiple rows.For more information about the syntax and arguments of this clause, see FROM Transact SQL.ON lt mergesearchcondition Specifies the conditions on which lt tablesource is joined with targettable to determine where they match.Caution It is important to specify only the columns from the target table that are used for matching purposes.That is, specify columns from the target table that are compared to the corresponding column of the source table.Do not attempt to improve query performance by filtering out rows in the target table in the ON clause, such as by specifying AND NOT targettable.Doing so may return unexpected and incorrect results.WHEN MATCHED THEN lt mergematched Specifies that all rows of targettable that match the rows returned by lt tablesource ON lt mergesearchcondition, and satisfy any additional search condition, are either updated or deleted according to the lt mergematched clause.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 lt searchcondition 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.If UPDATE is specified in the lt mergematched clause, and more than one row of lt tablesource matches a row in targettable based on lt mergesearchcondition, SQL Server returns an error.The MERGE statement cannot update the same row more than once, or update and delete the same row.WHEN NOT MATCHED BY TARGET THEN lt mergenotmatched Specifies that a row is inserted into targettable for every row returned by lt tablesource ON lt mergesearchcondition that does not match a row in targettable, but does satisfy an additional search condition, if present.The values to insert are specified by the lt mergenotmatched clause.The MERGE statement can have only one WHEN NOT MATCHED clause.WHEN NOT MATCHED BY SOURCE THEN lt mergematched Specifies that all rows of targettable that do not match the rows returned by lt tablesource ON lt mergesearchcondition, and that satisfy any additional search condition, are either updated or deleted according to the lt mergematched clause.The MERGE statement can have at most two WHEN NOT MATCHED BY SOURCE clauses.If two clauses are specified, then the first clause must be accompanied by an AND lt clausesearchcondition clause.For any given row, the second WHEN NOT MATCHED BY SOURCE clause is only applied if the first is not.If there are two WHEN NOT MATCHED BY SOURCE clauses, then one must specify an UPDATE action and one must specify a DELETE action.Only columns from the target table can be referenced in lt clausesearchcondition.When no rows are returned by lt tablesource, columns in the source table cannot be accessed.If the update or delete action specified in the lt mergematched clause references columns in the source table, error 2.Invalid column name is returned.For example, the clause WHEN NOT MATCHED BY SOURCE THEN UPDATE SET Target.Table.Col. 1 Source.Table.
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