CREATE DEFAULT (Transact-SQL)

Artigo
12/03/2008

Creates an object called a default. When bound to a column or an alias data type, a default specifies a value to be inserted into the column to which the object is bound (or into all columns, in the case of an alias data type), when no value is explicitly supplied during an insert.

Important

CREATE DEFAULT will be removed in a future version of Microsoft SQL Server. Avoid using CREATE DEFAULT in new development work, and plan to modify applications that currently use it. Instead, use default definitions created using the DEFAULT keyword of ALTER TABLE or CREATE TABLE. For more information, see Creating and Modifying DEFAULT Definitions.

Topic link icon Transact-SQL Syntax Conventions

Syntax

CREATE DEFAULT [ schema_name . ] default_name 
AS constant_expression [ ; ]

Arguments

schema_name
Is the name of the schema to which the default belongs.

default_name
Is the name of the default. Default names must conform to the rules for identifiers. Specifying the default owner name is optional.

constant_expression
Is an expression that contains only constant values (it cannot include the names of any columns or other database objects). Any constant, built-in function, or mathematical expression can be used, except those that contain alias data types. User-defined functions cannot be used.. Enclose character and date constants in single quotation marks ('); monetary, integer, and floating-point constants do not require quotation marks. Binary data must be preceded by 0x, and monetary data must be preceded by a dollar sign ($). The default value must be compatible with the column data type.

Remarks

A default name can be created only in the current database. Within a database, default names must be unique by schema. When a default is created, use sp_bindefault to bind it to a column or to an alias data type.

If the default is not compatible with the column to which it is bound, SQL Server generates an error message when trying to insert the default value. For example, N/A cannot be used as a default for a numeric column.

If the default value is too long for the column to which it is bound, the value is truncated.

CREATE DEFAULT statements cannot be combined with other Transact-SQL statements in a single batch.

A default must be dropped before creating a new one of the same name, and the default must be unbound by executing sp_unbindefault before it is dropped.

If a column has both a default and a rule associated with it, the default value must not violate the rule. A default that conflicts with a rule is never inserted, and SQL Server generates an error message each time it attempts to insert the default.

When bound to a column, a default value is inserted when:

A value is not explicitly inserted.
Either the DEFAULT VALUES or DEFAULT keywords are used with INSERT to insert default values.

If NOT NULL is specified when creating a column and a default is not created for it, an error message is generated when a user fails to make an entry in that column. The following table illustrates the relationship between the existence of a default and the definition of a column as NULL or NOT NULL. The entries in the table show the result.

Column definition	No entry, no default	No entry, default	Enter NULL, no default	Enter NULL, default
NULL	NULL	default	NULL	NULL
NOT NULL	Error	default	error	error

Note

Whether SQL Server interprets an empty string as a single space or as a true empty string is controlled by the sp_dbcmptlevel setting. If the compatibility level is less than or equal to 65, SQL Server interprets empty strings as single spaces. If the compatibility level is equal to 70, SQL Server interprets empty strings as empty strings. For more information, see sp_dbcmptlevel (Transact-SQL).

To rename a default, use sp_rename. For a report on a default, use sp_help.

Permissions

To execute CREATE DEFAULT, at a minimum, a user must have CREATE DEFAULT permission in the current database and ALTER permission on the schema in which the default is being created.

Examples

A. Creating a simple character default

The following example creates a character default called unknown.

USE AdventureWorks;
GO
CREATE DEFAULT phonedflt AS 'unknown';

B. Binding a default

The following example binds the default created in example A. The default takes effect only if no entry is specified for the Phone column of the Contact table. Note that omitting any entry is different from explicitly stating NULL in an INSERT statement.

Because a default named phonedflt does not exist, the following Transact-SQL statement fails. This example is for illustration only.

USE AdventureWorks;
GO
sp_bindefault 'phonedflt', 'Person.Contact.Phone';

Partilhar via

CREATE DEFAULT (Transact-SQL)

Syntax

Arguments

Remarks

Permissions

Examples

A. Creating a simple character default

B. Binding a default

See Also

Reference

Other Resources

Help and Information

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