What is deferrable initially deferred?
With DEFERRABLE INITIALLY IMMEDIATE you can defer the constraints on demand when you need it. This is useful if you normally want to check the constraints at statement time, but for e.g. a batch load want to defer the checking until commit time.
What are the constraints in Oracle explain primary key constraints with examples?
The PRIMARY KEY constraint uniquely identifies each record in a table. Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).
When you drop a primary key constraint if the primary key was created using an existing index object then?
When you drop a primary key constraint: If the primary key was created using an existing index, then the index is not dropped. If the primary key was created using a system-generated index, then the index is dropped.
What are primary key constraints?
The PRIMARY KEY constraint specifies that the constrained columns’ values must uniquely identify each row. A table’s primary key should be explicitly defined in the CREATE TABLE statement. Tables can only have one primary key.
Which statement is wrong about primary key constraint in SQL?
Which statement is wrong about PRIMARY KEY constraint in SQL? Primary keys must contain UNIQUE values.
Can I remove index from primary key?
E. Indexes that are created as the result of creating PRIMARY KEY or UNIQUE constraints cannot be dropped by using DROP INDEX. They are dropped using the ALTER TABLE DROP CONSTRAINT statement.
Can we drop primary key constraint?
To drop primary key constraints, use the DROP PRIMARY KEY clause of the ALTER TABLE statement. Alternatively, you can use the ALTER TABLE statement with the DROP CONSTRAINT option. To drop foreign key (referential) constraints, use the DROP CONSTRAINT clause of the ALTER TABLE statement.
How do you write a primary key constraint?
The syntax to create a primary key using the ALTER TABLE statement in SQL is: ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (column1, column2, column_n);
Why are the primary keys not deferrable in Oracle?
The reasoning behind having the primary keys as not being deferrable was due to uniqueness not being enforced until commit time, and I get the impression that lookups using the index on a deferrable Constraint will be slower than the lookups using the index on a normal constraint because uniqueness is not enforced on deferrable constraints.
Why are foreign keys used as deferrable constraints?
The reasoning for having the foreign keys as being deferrable,initially deferred was to allow for easier programming in the application. There was no need to alter the constraints to be deferred or to worry about the order of inserts into the tables. Is this a sensible guideline to follow for using deferred integrity constraints.
How are view constraints enforced in Oracle Database?
View Constraints Oracle Database does not enforce view constraints. However, you can enforce constraints on views through constraints on base tables. You can specify only unique, primary key, and foreign key constraints on views, and they are supported only in DISABLE NOVALIDATE mode.
How to create a FOREIGN KEY constraint in Oracle?
To create a foreign key constraint, in addition, the parent table or view must be in your own schema or you must have the REFERENCES privilege on the columns of the referenced key in the parent table or view. ( inline_constraint::=, out_of_line_constraint::=, inline_ref_constraint::=, out_of_line_ref_constraint::=)