- 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:
| Column Name | Description |
| 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.
Example:
SELECT OWNER, CONSTRAINT_NAME, CONSTRAINT_TYPE,
SEARCH_CONSTRAINT, TABLE_NAME FROM USER_CONSTRAINTS;