# columnDefinition

    simpleColumnName [ dataType ]
        [ columnLevelConstraint ]*
        [ [ WITH ] DEFAULT defaultConstantExpression
           | generatedColumnSpec
           | generationClause
        ]
        [ columnLevelConstraint ]*

The syntax of dataType is described in Data types. The dataType can be omitted only if you specify a generationClause. If you omit the dataType, the type of the generated column is the type of the generationClause. If you specify both a dataType and a generationClause, the type of the generationClause must be assignable to dataType.

The syntaxes of columnLevelConstraint and tableLevelConstraint are described in CONSTRAINT clause.

## Column default

For the definition of a default value, a defaultConstantExpression is an expression that does not refer to any table. It can include constants, date-time special registers, current schemas, users, roles, and null:

    defaultConstantExpression:
              NULL
            | CURRENT { SCHEMA | SQLID }
            | USER | CURRENT_USER | SESSION_USER | CURRENT_ROLE
            | DATE
            | TIME
            | TIMESTAMP
            | CURRENT DATE | CURRENT_DATE
            | CURRENT TIME | CURRENT_TIME
            | CURRENT TIMESTAMP | CURRENT_TIMESTAMP
            | literal

For details about Derby literal values, see Data types.

The values in a defaultConstantExpression must be compatible in type with the column, but a defaultConstantExpression has the following additional type restrictions:

- If you specify USER, CURRENT_USER, SESSION_USER, or CURRENT_ROLE, the column must be a character column whose length is at least 8.
- If you specify CURRENT SCHEMA or CURRENT SQLID, the column must be a character column whose length is at least 128.
- If the column is an integer type, the default value must be an integer literal.
- If the column is a decimal type, the scale and precision of the default value must be within those of the column.

Parent topic: CREATE TABLE statement
Related reference
generatedColumnSpec
generationClause