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The DEFAULT clause lets you specify a value to be assigned to the column if a subsequent INSERT statement omits a value for the column. The data type of the expression must match the data type specified for the column. The column must also be large enough to hold this expression.
The DEFAULT expression can include any SQL function as long as the function does not return a literal argument, a column reference, or a nested function invocation.
The DEFAULT expression can include the sequence pseudocolumns CURRVAL and NEXTVAL, as long as the sequence exists and you have the privileges necessary to access it. Users who perform subsequent inserts that use the DEFAULT expression must have the INSERT privilege on the table and the SELECT privilege on the sequence. If the sequence is later dropped, then subsequent INSERT statements where the DEFAULT expression is used will result in an error. If you do not fully qualify the sequence by specifying the sequence owner, for example, SCOTT.SEQ1, then Oracle Database will default the sequence owner to be the user who issues the CREATE TABLE statement. For example, if user MARY creates SCOTT.TABLE and refers to a sequence that is not fully qualified, such as SEQ2, then the column will use sequence MARY.SEQ2. Synonyms on sequences undergo a full name resolution and are stored as the fully qualified sequence in the data dictionary; this is true for public and private synonyms. For example, if user BETH adds a column referring to public or private synonym SYN1 and the synonym refers to PETER.SEQ7, then the column will store PETER.SEQ7 as the default.
Restrictions on Default Column Values Default column values are subject to the following restrictions:
A DEFAULT expression cannot contain references to PL/SQL functions or to other columns, the pseudocolumns LEVEL, PRIOR, and ROWNUM, or date constants that are not fully specified.
The expression can be of any form except a scalar subquery expression.