- We can use describe command to view logical structure of the table.
- It displays table structure including column name, data type, size & not null constant.
- It does not provide information about other constraint such as primary key, foreign key, unique key and so on.
- Oracle maintains in built table known as USER_CONSTRAINTS.
- It stores information about the constraints for different tables
- If we ever wish to check information about different constraints defined by the user on different tables then USER_CONSTRAINTS table can be helpful.
- It contains following fields:
|Owner||The owner of the constraint|
|Table_name||Name of the table|
|Constraint_name||Displays name of constraint|
|Constraint_type||Displays constraint type:
1. PK – Primary key 2. R – Foreign key 3. U – Unique key
C – Check key
|R_owner||Owner of the referenced table|
|Search_condition||Search condition for check constraint|
|R_constraint_name||Constraint name for the reference key|
- We can use SELECT statement to access information from the USER_CONSTRAINTS are follow.
SELECT OWNER, CONSTRAINT_NAME, CONSTRAINT_TYPE, SEARCH_CONSTRAINT, TABLE_NAME FROM USER_CONSTRAINTS;