Changing the Data Type Assigned to a Column

A column’s data type determines what kind of data can be stored in the column. A list of system-defined data types appears in the Data type property column in Column Properties view.

You can choose the appropriate data type for the information you want to store in the column. If user-defined data types exist for your database, they appear at the end of the Datatype list. The system-defined data type that corresponds to the user-defined data type appears in parentheses at the end of the user-defined data type name. For example: “id (varchar).”

Special Considerations for Assigning a User-defined Data Type to a Column

• Selecting a data type automatically sets the length, precision, and scale for the column based on the data type’s definition.

  You cannot change these settings for user-defined data types.

• You can change the Allow Nulls setting only if the user-defined data type allows null values.
• When you select a user-defined data type, the Default setting is blank, even if a bound default is defined for the data type.

  You can check whether a bound default exists by saving the table and reloading it into memory. When you reopen the table, the bound default appears in the Default Value cell. If you set a default value for a column that already has a bound default, an error message prompts you to remove your entry.

Note Changing the data type re-creates the table in the database when you save the table or diagram.

Caution If this column is related to columns in other tables, then the data type of the related columns must also be changed to preserve referential integrity. When you save the table or diagram, the Data type Change Required dialog box enables you to change the data type of the related columns automatically.

See Also

Creating User-Defined Data Types