5.3 Constraint Views

There are two data dictionary views that provide you detailed information about constraints. These are USER_CONSTRAINTS and USER_CONS_COLUMNS.

A table can have no constraints, or many. For every constraint in a table there is a row in USER_CONSTRAINTS that describes that particular constraint, including the table name to which that constraint is applied. If you know a constraint name and you want to know the constraint type, query USER_CONSTRAINTS. This view describes the constraint definition. It does not provide you with the column name (s) on which that constraint is defined.

The USER_CONS_COLUMNS view shows the columns in a constraint. If a primary key is a concatenated key, there will be two rows for that constraint in this view. Each column in the concatenated primary key constraint will have a row, and each row will differ by POSITION ”this indicates the position of a column with respect to concatenated column constraints.

The following table highlights the joining columns of these views. USER_CONSTRAINTS and USER_CONS_COLUMNS each have the column CONSTRAINT_NAME and TABLE_NAME.

USER_CONSTRAINTS	USER_CONST_COLUMNS
CONSTRAINT_NAME	CONSTRAINT_NAME
CONSTRAINT_TYPE	TABLE_NAME
TABLE_NAME	COLUMN_NAME
	POSITION