FirebirdSQL logo
 DOMAININDEX 

Setting a DEFAULT Value

The optional DEFAULT clause allows you to specify the default value for the table column.This value will be added to the column when an INSERT statement is executed and that column was omitted from the INSERT command or DEFAULT was used instead of a value expression.The default value will also be used in UPDATE when DEFAULT is used instead of a value expression.

The default value can be a literal of a compatible type, a context variable that is type-compatible with the data type of the column, or NULL, if the column allows it.If no default value is explicitly specified, NULL is implied.

An expression cannot be used as a default value.

Domain-based Columns

To define a column, you can use a previously defined domain.If the definition of a column is based on a domain, it may contain a new default value, additional CHECK constraints, and a COLLATE clause that will override the values specified in the domain definition.The definition of such a column may contain additional column constraints (for instance, NOT NULL), if the domain does not have it.

Important

It is not possible to define a domain-based column that is nullable if the domain was defined with the NOT NULL attribute.If you want to have a domain that might be used for defining both nullable and non-nullable columns and variables, it is better practice defining the domain nullable and apply NOT NULL in the downstream column definitions and variable declarations.