Module 10Merging Data and

Passing Tables

Module Overview• Using the MERGE Statement• Implementing Table Types• Using Table Types As Parameters

Lesson 1: Using the MERGE Statement• MERGE Statement• WHEN MATCHED• WHEN NOT MATCHED BY TARGET• WHEN NOT MATCHED BY SOURCE• OUTPUT Clause and $action• MERGE Determinism and Performance• Demonstration 1A: MERGE Statement

MERGE Statement

MERGE INTO dbo.Employee AS eUSING dbo.EmployeeUpdate AS euON e.EmployeeID = eu.EmployeeID…

• Modifies data in a target table (or updatable view or CTE) based on the results of a join with a source table

• Commonly used to populate data warehouses INSERT data if not already present UPDATE data if already present

• Target table plus a source rowset• Must specify how the source and target are joined

WHEN MATCHED

MERGE INTO dbo.Employee AS eUSING dbo.EmployeeUpdate AS euON e.EmployeeID = eu.EmployeeIDWHEN MATCHED THEN UPDATE SET e.FullName = eu.FullName, e.EmploymentStatus = eu.EmploymentStatus

• Clause that defines the action to be taken when the row in the source is found in the target

• Specifies the data modifications to take place – can be INSERT, UPDATE or DELETE

• Two WHEN MATCHED clauses can be included – needs an extra predicate on the first WHEN MATCHED AND s.Quantity > 0 One must be an UPDATE, the other a DELETE

WHEN NOT MATCHED BY TARGET

MERGE INTO dbo.Employee AS eUSING dbo.EmployeeUpdate AS euON e.EmployeeID = eu.EmployeeIDWHEN MATCHED THEN UPDATE SET e.FullName = eu.FullName, e.EmploymentStatus = eu.EmploymentStatusWHEN NOT MATCHED THEN INSERT (EmployeeID,FullName,EmploymentStatus) VALUES (eu.EmployeeID,eu.FullName,eu.EmploymentStatus);

• Clause that defines the action to be taken when the row in the source cannot be found in the target

• The words BY TARGET are optional and often omitted

WHEN NOT MATCHED BY SOURCE

MERGE INTO dbo.Employee AS eUSING dbo.EmployeeUpdate AS euON e.EmployeeID = eu.EmployeeIDWHEN MATCHED THEN UPDATE SET e.FullName = eu.FullName, e.EmploymentStatus = eu.EmploymentStatusWHEN NOT MATCHED THEN INSERT (EmployeeID,FullName,EmploymentStatus) VALUES (eu.EmployeeID,eu.FullName,eu.EmploymentStatus)WHEN NOT MATCHED BY SOURCE THEN DELETE;

• Clause that defines the action to be taken for rows in the target that were not supplied in the source

• Not commonly used but typically involve a DELETE

OUTPUT Clause and $action

MERGE INTO dbo.Employee AS eUSING dbo.EmployeeUpdate AS euON e.EmployeeID = eu.EmployeeIDWHEN MATCHED THEN UPDATE SET e.FullName = eu.FullName, e.EmploymentStatus = eu.EmploymentStatusWHEN NOT MATCHED THEN INSERT (EmployeeID,FullName,EmploymentStatus) VALUES (eu.EmployeeID,eu.FullName,eu.EmploymentStatus)OUTPUT $action,inserted.EmployeeID,deleted.EmployeeID;

• OUTPUT clause can also be used with MERGE• $action used to determine the action taken for each row

MERGE Determinism and Performance• Matching source and destination rows using MERGE is not

the same as matching with UPDATE• UPDATE can allow a source row to update multiple target

rows• MERGE joins must be deterministic – an incoming row

must only match a single target row • MERGE performs well as it makes only a single pass

through the data Often better performance than separate INSERT, UPDATE and

DELETE statements

Demonstration 1A: MERGE StatementIn this demonstration you will see:• How to use the MERGE statement• How to use the OUTPUT clause with the MERGE statement• How to perform optional updates with MERGE• How to use MERGE as a composable query• How to use the VALUES clause as a MERGE source

Lesson 2: Implementing Table Types• Reducing Round-Trip Overhead• Options for Passing Lists as Parameters• Demonstration 2A: Passing Delimited Lists• Introduction to the TABLE Type• Populating TABLE Types with Row Constructors• Demonstration 2B: TABLE Types and Row Constructors

Reducing Round-Trip Overhead• Round-trip to from an application to SQL Server and back

can be substantial Common aim to minimize the impact of round trips

• Many operations include many round-trips and cause transactions to last longer than desirable

• Add an order Start Transaction Save Order Header Save Order Detail Line 1 Save Order Detail Line 2 Save Order Detail Line 3 Commit Transaction

Options for Passing Lists as Parameters• Prior to SQL Server 2008, options for passing lists of values

in a single call were limited• Delimited Lists (often comma-delimited)

Required writing custom parsing logic Loose structure Loose data typing

• XML Also requires some complex parsing logic Semi-structured Loose data typing without schemas

Demonstration 2A: Passing Delimited ListsIn this demonstration, you will see• How to query a table-valued function that performs list

parsing• How the function allows for different delimiters• How to use the function in a join• How common errors can occur with delimited lists

Introduction to the TABLE Type

CREATE TYPE dbo.CustomerBalanceAS TABLE ( CustomerID int, CurrentBalance decimal(18,2));GO

• Earlier versions of SQL Server allowed variables to be of type TABLE and to allow definition of the structure of the table

• SQL Server allows the creation of table data type definitions Can be used for variables Can be used for parameters

Populating TABLE Types with Row Constructors

DECLARE @Balance dbo.CustomerBalance;

INSERT INTO @Balance VALUES (12,14.50),(15,13.75),(22,19.50);

• SQL Server allows the population of multiple rows of data into a table variable via row constructors Can be used with both INSERT and MERGE statements

• Multi-row inserts are atomic operations All inserts occur or none occur

Demonstration 2B: TABLE Types and Row ConstructorsIn this demonstration you will see:• How to work with row constructors• How to declare a table data type• How to work with variables with user-defined table data

types

Lesson 3: Using TABLE Types As Parameters• TABLE Input Parameters for Stored Procedures• Using Row Constructors to Populate Parameters• Demonstration 3A: Passing Tables to Stored Procedures

TABLE Input Parameters for Stored Procedures

CREATE TYPE dbo.SalesDetails AS TABLE( Description varchar(50), Price decimal(18,2));GOCREATE PROCEDURE dbo.SalesInsert @CustomerID int, @PurchaseOrderNumber varchar(20), @SalesDetails dbo.SalesDetails READONLY, @SaleID int OUTPUTAS BEGIN

• User-defined table data types can be used as input parameters for stored procedures

• Not able to be used for output parameters• Must include READONLY in the definition

Using Row Constructors to Populate Parameters

DECLARE @SaleID int;DECLARE @SalesDetails dbo.SalesDetails;

INSERT INTO @SalesDetails VALUES('Product 1',12.3), ('Product 2',14.66), ('Product 3',122.35);EXEC dbo.SalesInsert 12,'BigOrder',@SalesDetails,@SaleID OUTPUT;

• Table variables are created to provide the parameters to pass to stored procedures with table-valued parameters

• Row constructors are ideal for populating the table variables prior to making the stored procedure call

Demonstration 3A: Passing Tables to Stored ProceduresIn this demonstration you will see:• How traditional stored procedure calls often involve

multiple round trips to the server• How to declare a table data type• How to use the table data type to avoid round trips• How to view catalog information about the table data

types by querying the sys.types and sys.table_types system views

Lab 10: Passing Tables and Merging Data• Exercise 1: Create a Table Type • Exercise 2: Use a Table Type Parameter• Challenge Exercise 3: Use a Table Type with MERGE (Only if

time permits)

Logon information

Estimated time: 45 minutes

Virtual machine 623XB-MIA-SQLUser name AdventureWorks\AdministratorPassword Pa$$w0rd

Lab ScenarioIn earlier versions of SQL Server, passing lists of values to stored procedures was a challenge. SQL Server 2008 introduced the table type and table-valued parameters. In this lab, you will create a replacement stored procedure Reports.GetProductsByColorList_Test that uses a table-valued parameter to replace an existing stored procedure Reports.GetProductsByColorList that was based on passing a comma-delimited list of values. You will then create a new procedure that processes complete rows of data and performs updates using the MERGE statement.

Lab Review• What is the purpose of the OUTPUT clause?• In the values returned by an OUTPUT clause, how can we

tell if an INSERT, UPDATE or DELETE occurred?

Module Review and Takeaways• Review Questions• Best Practices