Článek
10/01/2010

Table Value Constructor (Transact-SQL)

Specifies a set of row value expressions to be constructed into a table. The Transact-SQL table value constructor allows multiple rows of data to be specified in a single DML statement. The table value constructor can be specified in the VALUES clause of the INSERT statement, in the USING <source table> clause of the MERGE statement, and in the definition of a derived table in the FROM clause.

Topic link icon Transact-SQL Syntax Conventions

Syntax

VALUES ( <row value expression list> ) [ ,...n ] 

<row value expression list> ::=
    {<row value expression> } [ ,...n ]

<row value expression> ::=
    { DEFAULT | NULL | expression }

Arguments

VALUES
Introduces the row value expression lists. Each list must be enclosed in parentheses and separated by a comma.

The number of values specified in each list must be the same and the values must be in the same order as the columns in the table. A value for each column in the table must be specified or the column list must explicitly specify the columns for each incoming value.
DEFAULT
Forces the Database Engine to insert the default value defined for a column. If a default does not exist for the column and the column allows null values, NULL is inserted. DEFAULT is not valid for an identity column. When specified in a table value constructor, DEFAULT is allowed only in an INSERT statement.
expression
Is a constant, a variable, or an expression. The expression cannot contain an EXECUTE statement.

Limitations and Restrictions

The maximum number of rows that can be constructed using the table value constructor is 1000. To insert more than 1000 rows, create multiple INSERT statements, or bulk import the data by using the bcp utility or the BULK INSERT statement.

Only single scalar values are allowed as a row value expression. A subquery that involves multiple columns is not allowed as a row value expression. For example, the following code results in a syntax error because the third row value expression list contains a subquery with multiple columns.

USE AdventureWorks;
GO
CREATE TABLE dbo.MyProducts (Name varchar(50), ListPrice money);
GO
-- This statement fails because the third values list contains multiple columns in the subquery.
INSERT INTO dbo.MyProducts (Name, ListPrice)
VALUES ('Helmet', 25.50),
       ('Wheel', 30.00),
       (SELECT Name, ListPrice FROM Production.Product WHERE ProductID = 720);
GO

However, the statement can be rewritten by specifying each column in the subquery separately. The following example successfully inserts three rows into the MyProducts table.

INSERT INTO dbo.MyProducts (Name, ListPrice)
VALUES ('Helmet', 25.50),
       ('Wheel', 30.00),
       ((SELECT Name FROM Production.Product WHERE ProductID = 720),
        (SELECT ListPrice FROM Production.Product WHERE ProductID = 720));
GO

Data Types

The values specified in a multi-row INSERT statement follow the data type conversion properties of the UNION ALL syntax. This results in the implicit conversion of unmatched types to the type of higher precedence. If the conversion is not a supported implicit conversion, an error is returned. For example, the following statement inserts an integer value and a character value into a column of type char.

CREATE TABLE dbo.t (a int, b char);
GO
INSERT INTO dbo.t VALUES (1,'a'), (2, 1);
GO

When the INSERT statement is run, SQL Server tries to convert 'a' to an integer because the data type precedence indicates that an integer is of a higher type than a character. The conversion fails and an error is returned. You can avoid the error by explicitly converting values as appropriate. For example, the previous statement can be written as follows.

INSERT INTO dbo.t VALUES (1,'a'), (2, CONVERT(CHAR,1));

Examples

A. Inserting multiple rows of data

The following example creates the table dbo.Departments and then uses the table value constructor to insert five rows into the table. Because values for all columns are supplied and are listed in the same order as the columns in the table, the column names do not have to be specified in the column list.

USE AdventureWorks;
GO
INSERT INTO Production.UnitMeasure
VALUES (N'FT2', N'Square Feet ', '20080923'), (N'Y', N'Yards', '20080923'), (N'Y3', N'Cubic Yards', '20080923');
GO

B. Inserting multiple rows with DEFAULT and NULL values

The following example demonstrates specifying DEFAULT and NULL when using the table value constructor to insert rows into a table.

USE AdventureWorks;
GO
CREATE TABLE Sales.MySalesReason(
    SalesReasonID int IDENTITY(1,1) NOT NULL,
    Name dbo.Name NULL ,
    ReasonType dbo.Name NOT NULL DEFAULT 'Not Applicable' );
GO
INSERT INTO Sales.MySalesReason 
VALUES ('Recommendation','Other'), ('Advertisement', DEFAULT), (NULL, 'Promotion');

SELECT * FROM Sales.MySalesReason;

C. Specifying multiple values as a derived table in a FROM clause

The following example uses the table value constructor to specify multiple values in the FROM clause of a SELECT statement.

SELECT a, b FROM (VALUES (1, 2), (3, 4), (5, 6), (7, 8), (9, 10) ) AS MyTable(a, b);
GO

D. Specifying multiple values as a derived source table in a MERGE statement

The following example uses MERGE to modify the SalesReason table by either updating or inserting rows. When the value of NewName in the source table matches a value in the Name column of the target table, (SalesReason), the ReasonType column is updated in the target table. When the value of NewName does not match, the source row is inserted into the target table. The source table is a derived table that uses the Transact-SQL table value constructor to specify multiple rows for the source table.

USE AdventureWorks;
GO
-- Create a temporary table variable to hold the output actions.
DECLARE @SummaryOfChanges TABLE(Change VARCHAR(20));

MERGE INTO Sales.SalesReason AS Target
USING (VALUES ('Recommendation','Other'), ('Review', 'Marketing'), ('Internet', 'Promotion'))
       AS Source (NewName, NewReasonType)
ON Target.Name = Source.NewName
WHEN MATCHED THEN
    UPDATE SET ReasonType = Source.NewReasonType
WHEN NOT MATCHED BY TARGET THEN
    INSERT (Name, ReasonType) VALUES (NewName, NewReasonType)
OUTPUT $action INTO @SummaryOfChanges;

-- Query the results of the table variable.
SELECT Change, COUNT(*) AS CountPerChange
FROM @SummaryOfChanges
GROUP BY Change;

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