Table-Valued Parameters (Database Engine)
Table-valued parameters are declared by using user-defined table types. You can use table-valued parameters to send multiple rows of data to a Transact-SQL statement or a routine, such as a stored procedure or function, without creating a temporary table or many parameters.
Table-valued parameters are like parameter arrays in OLE DB and ODBC, but offer more flexibility and closer integration with Transact-SQL. Table-valued parameters also have the benefit of being able to participate in set-based operations.
Transact-SQL passes table-valued parameters to routines by reference to avoid making a copy of the input data. You can create and execute Transact-SQL routines with table-valued parameters, and call them from Transact-SQL code, managed and native clients in any managed language.
A table-valued parameter is scoped to the stored procedure, function, or dynamic Transact-SQL text, exactly like other parameters. Similarly, a variable of table type has a scope like any other local variable that is created by using a DECLARE statement. You can declare table-valued variables within dynamic Transact-SQL statements and pass these variables as table-valued parameters to stored procedures and functions.
Table-valued parameters offer more flexibility and in some cases better performance than temporary tables or other ways to pass a list of parameters. Table-valued parameters offer the following benefits:
- Do not acquire locks for the initial population of data from a client.
- Provide a simple programming model.
- Enable you to include complex business logic in a single routine.
- Reduce round trips to the server.
- Can have a table structure of different cardinality.
- Are strongly typed.
- Enable the client to specify sort order and unique keys.
- Are cached like a temp table when used in a stored procedure. Starting with SQL Server 2012 (11.x), table-valued parameters are also cached for parameterized queries.
Table-valued parameters have the following restrictions:
- SQL Server does not maintain statistics on columns of table-valued parameters.
- Table-valued parameters must be passed as input READONLY parameters to Transact-SQL routines. You cannot perform DML operations such as UPDATE, DELETE, or INSERT on a table-valued parameter in the body of a routine.
- You cannot use a table-valued parameter as the target of a SELECT INTO or INSERT EXEC statement. A table-valued parameter can be in the FROM clause of SELECT INTO or in the INSERT EXEC string or stored procedure.
Table-Valued Parameters vs. BULK INSERT Operations
Using table-valued parameters is comparable to other ways of using set-based variables; however, using table-valued parameters frequently can be faster for large data sets. Compared to bulk operations that have a greater startup cost than table-valued parameters, table-valued parameters perform well for inserting less than 1000 rows.
Table-valued parameters that are reused benefit from temporary table caching. This table caching enables better scalability than equivalent BULK INSERT operations. By using small row-insert operations a small performance benefit might be gained by using parameter lists or batched statements instead of BULK INSERT operations or table-valued parameters. However, these methods are less convenient to the program, and performance decreases quickly as rows increase.
Table-valued parameters perform equally well or better than an equivalent parameter array implementation.