Oracle Database: Show All Table Constraints for a User

Purpose

This Oracle SQL query is designed to retrieve a comprehensive list of all constraints associated with tables owned by a specific user in your Oracle database. Constraints are essential rules that ensure data integrity and consistency. This query offers a clear and organized view of these constraints, aiding in database management and troubleshooting.

Sample SQL Command

 1set lines 100 pages 999
 2break on table_name
 3select 	table_name
 4,	decode(constraint_type, 
 5        	'C', 'Check', 
 6	        'O', 'R/O View', 
 7	        'P', 'Primary', 
 8	        'R', 'Foreign', 
 9	        'U', 'Unique', 
10	        'V', 'Check view') type
11,	nvl(index_name, R_CONSTRAINT_NAME) "IDX"
12from 	dba_constraints
13where	owner like '&user'
14order	by table_name
15,	decode(constraint_type, 
16	'P','0','R','1','U','2','C','3','O','4','V','5')
17/

Code Breakdown

1. set lines 100 pages 999: Sets the output formatting for better readability.
2. break on table_name: Organizes the results by grouping them based on table names.
3. select table_name, decode(constraint_type, ... ) type, nvl(index_name, R_CONSTRAINT_NAME) "IDX": Selects three columns:
   • table_name: The name of the table the constraint is applied to.
   • type: Decodes the constraint type code (C, O, P, R, U, V) into human-readable descriptions (Check, Read-Only View, Primary Key, Foreign Key, Unique, Check View).
   • "IDX": Shows the associated index name (if available) or the name of the referenced constraint for foreign keys.
4. from dba_constraints: Queries the dba_constraints data dictionary view, which stores information about all constraints in the database.
5. where owner like '&user': Filters the results to only include constraints for tables owned by the specified user. You'll be prompted to enter the username when running this query.
6. order by table_name, decode(constraint_type, ... ): Sorts the output first by table name and then by constraint type, following a specific priority order (Primary Key, Foreign Key, Unique, Check, Read-Only View, Check View).

Key Points:

• Data Dictionary View: Leverages the dba_constraints view to access constraint metadata.
• Constraint Type Decoding: Translates cryptic constraint type codes into meaningful descriptions.
• Index Information: Includes the index name associated with the constraint, if applicable.
• User Filtering: Allows you to focus on constraints related to a specific user's tables.
• Organized Output: Presents the results in a sorted and easy-to-interpret format.
• Note: This query requires you to have the necessary privileges to access the dba_constraints view. If you encounter permission issues, consider using the all_constraints or user_constraints views, which have less restrictive access requirem

Insights:

• Understanding the constraints on your tables is crucial for database design, maintenance, and troubleshooting.
• This query empowers you to quickly identify the types of constraints applied to each table.
• It helps you pinpoint potential issues like foreign key violations or conflicts with unique constraints.

Explanations:

• The decode function is used to translate the constraint type code into a more understandable format.
• The nvl function ensures that an index name or referenced constraint name is displayed, even if one is not directly associated with the constraint.
• The order by clause with nested decode prioritizes the display of constraint types.

References:

• Oracle Database SQL Reference: DECODE Function
• Oracle Database SQL Reference: NVL Function
• Oracle Database Reference: DBA_CONSTRAINTS View