I want to know if there is some specific way to obtain a table-level check constraint in Oracle and in PostgreSQL.
I can obtain all the check constraints in a table, but I want to obtain only this specific check constraint, I don't know if there is any specific query.
Thanks!
In PostgreSQL there is a System Catalog pg_constraint.
The catalog pg_constraint stores check, primary key, unique, foreign
key, and exclusion constraints on tables. (Column constraints are not
treated specially. Every column constraint is equivalent to some table
constraint.) Not-null constraints are represented in the pg_attribute
catalog, not here.
User-defined constraint triggers (created with CREATE CONSTRAINT
TRIGGER) also give rise to an entry in this table.
Check constraints on domains are stored here, too.
SELECT
*
FROM
pg_constraint
WHERE
contype = 'c' AND -- check constraint
conrelid != 0 AND -- table constraint
conname = 'my_check';
The contype column contains the constraint type, c is for check constraint.
The conrelid column contains the oid of the table this constraint is on, 0 if not a table constraint.
For Oracle basic view is ALL_CONSTRAINTS
Query, to obtain specific constraint in specific table:
SELECT *
FROM all_constraints
WHERE constraint_name LIKE upper('%&your_costraint%')
AND table_name LIKE upper('%&your_table%');
Related
Within the Oracle documentation, the (DBA|ALL|USER)_CONSTRAINTS view has the following columns (among others)
OWNER Owner of the constraint definition
CONSTRAINT_NAME Name of the constraint definition
TABLE_NAME Name associated with the table (or view) with constraint definition
My question is which of these columns uniquely identifies a constraint? Is it just OWNER and CONSTRAINT_NAME indicating that the constraint name must be unique within the scope of that OWNER schema, or is it OWNER, TABLE_NAME, and CONSTRAINT_NAME indicating that the constraint name must only be unique within the scope of that OWNER.TABLE_NAME?
According to documentation: https://docs.oracle.com/database/121/SQLRF/sql_elements008.htm#SQLRF00223
Each of the following schema objects has its own namespace:
Constraints
Which suggests, that uniquely identifiyng the constraint is it's name and the schema/owner of the constraint.
One point here - it depends what you consider 'unique'.
Let's consider you have a constraint. You will drop the constraint and recreate it with different definition. The constraint has still the same name, but it has a different OBJECT_ID from the database point of view - it is a different object.
It is still unique from the point of current state of the database, but not for the lifetime of it. So, if you want to make sure that you're still working with the same constraint (not only constrain with the same name as before), you might want to query OBJECT_ID.DBA/ALL/USER_OBJECTS instead.
I am working on this assignment question and it is asking me:
To create a table called (TEMP_CUST) from an existing table Customers
View the content and constraints of TEMP_CUST table
What I have done so far is I have created my table, didn't add any constraints to the table TEMP_CUST and viewed the table using the DESC command.
Here is the code for table creation
CREATE TABLE TEMP_CUST
AS
(SELECT
CUSTOMER#, LASTNAME,
FIRSTNAME, ADDRESS, CITY,
STATE, ZIP, REFERRED,
REGION, EMAIL
FROM
CUSTOMERS);
DESC TEMP_CUST;
Now that I have done that I want to view the constraints of the table. I have used this command but am not sure if it is correct.
SELECT *
FROM USER_CONSTRAINTS
WHERE TABLE_NAME = 'TEMP_CUST';
i have used this command, but not sure if it is correct.
You haven't said why you don't think it's correct so we have to guess the reason for your doubt. Perhaps it's because the set of constraints you get is smaller than the set of constraints for the original CUSTOMERS table?
That is correct. When we use CREATE TABLE ... AS SELECT the statement creates a new table with the projection, column names and datatypes of the original tables (assuming a vanilla SELECT clause) and the data (determined by the WHERE clause, if any). However, the only constraints which are created are NOT NULL constraints on the primary key column(s) and any other mandatory columns. The new table does not have primary key, foreign key or check constraints. We have to create these explicitly.
Hence, this query ...
SELECT * FROM USER_CONSTRAINTS
WHERE TABLE_NAME = 'TEMP_CUST';
... might return fewer constraints than you were expecting.
I need to modify an existing PK. Therefore I drop an recreate it.
ALTER TABLE B DROP CONSTRAINT PK_B;
ALTER TABLE B ADD CONSTRAINT PK_B PRIMARY KEY ("TYP", "NR", "HH", "QUART");
Unfortunately the last Statement will give me an error ORA-00955
If I create the PK constraint like it was defined originally with:
ALTER TABLE B ADD CONSTRAINT PK_B PRIMARY KEY ("TYP", "NR", "HH");
everything works fine.
Perhaps there is an INDEX associated with the PRIMARY KEY CONSTRAINT, and it is also named as PK_B.
You can check it as :
SELECT * FROM USER_INDEXES WHERE TABLE_NAME='<table_name>';
If that's true, then do :
ALTER INDEX "PK_B" RENAME TO "PK_XYZ";
Update : Regarding ALTER INDEX statement, few important points as mentioned by Justin in the comments
Oracle implicitly creates an UNIQUE index to support the PRIMARY KEY CONSTRAINT. Since, the index is of the same name that of the primary key, and now that the primary key is being modified, it is better to drop and re-create the index again as per the definition of the old primary key.
My conclusion :
The primary key constraint is enforced through a unique index.
If Oracle already finds an index – unique or non-unique – it uses it
for the primary key.
If the index was initially created as non-unique, it will continue to
show as non-unique, however it will actually be a unique index.
A good demonstration and quite detailed on other aspects too, by Arup : Primary Keys Guarantee Uniqueness? Think Again.
I had the same issue where I had to do the following to delete reference to a table from the view whilst recreating the database from the scratch. I was searching for the same in tables and indexes first.
connect sys/oracle as sysdba;
select * from all_tables
select * from all_indexes
(finally located the reference in the views)
select * from all_views where view_name like '%WKSTSTATE%';
drop view RUEGEN.WKSTSTATE;
I am working on a legacy oracle database system (10g) and I do not have detailed schema information. I need to find out if deleting a particular record in a table will cause cascading deletes in other tables. I have checked for triggers. But, I am not sure about cascading due to referential constraints. Is there a simple way to identify this?
Assuming you know (or can determine) the foreign key constraint(s) involved, you can look at the DELETE_RULE column from DBA_CONSTRAINTS
SELECT constraint_name, delete_rule
FROM dba_constraints
WHERE r_constraint_name = <<name of the primary key constraint>>
AND r_owner = <<owner of the primary key constraint>>
AND delete_rule = 'CASCADE'
will show you all the foreign key constraints that refer to a particular primary key constraint and will cascade the deletes. If you care about constraints that will do a SET NULL when the parent row is deleted, you could look for rows where the delete_rule was SET NULL as well.
Note that if you do not have privileges on the DBA_CONSTRAINTS table, you can use ALL_CONSTRAINTS instead assuming that you're really only concerned with tables that you have SELECT privileges on.
I have a oracle query as -
occupation varchar2(50) CHECK(occupation IN ('student','govt_service','private','business')));
now i need to remove the check constraint so i use the following query-
ALTER TABLE registration drop constraint occupation;
but since i haven't defined the constraint name it says invalid constraint name. Is there any way to delete the constraint ? I guess i can alter the table and add the name of the constraint, then delete it but is there any other way ?
run this query:
select * from all_constraints where table_name = 'REGISTRATION';
And you'll find the constraint name.
EDIT: I also recommend you to have a table Occupations and replace the current constraint with a foreign key. (If you are already want to do this, pls apologize me ). Further, normalising, the Occupations may have IDs and and the foreign should be defined on these ids.
Try querying USER_CONSTRAINTS table for CONSTRAINT_NAME, it must have generated a system name for the constraint you have created.
select * from USER_CONSTRAINTS
where owner='<your_schema>' and CONSTRAINT_TYPE='C';