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Explain several types of constraints that can be specified using CREATE TABLE command. Explain CASCADE and RESTRICT clauses of DROP SCHEMA command?Constraint DescriptionPRIMARY KEY Determines that column(s) uniquely identifies each record. The primary key cannot be NULL, and the data value(s) must be unique.
FOREIGN KEY In a one-to-many relationship, the constraint is added to the "many" table. The constraint ensures which if a value is entered into a specified column, it must already exist in the "one" table, or the record is not added.
UNIQUE Ensures that all data values stored in a specified column are unique.The UNIQUE constraint differs from the PRIMARY KEY constraint in which it permits NULL values.CHECK Ensures in which a specified condition is true before the data value is added to a table. For example, an order's ship date cannot be previous than its order date.
NOT NULL Ensures in which a specified column cannon contain a NULL value. The NOT NULL constraint can just be created along with the column-level approach to table creation.
Prevents the DROP from taking place if any dependent objects exists (RESTRICT) or causes all dependent objects do also be dropped (CASCADE).
Deadlock Prevention One of the easiest approaches for avoiding a deadlock would be to obtain all the locks at the begin of the transaction. Though, this approach restricts conc
Explain what is Aggregation ? Aggregation: This is used whenever we intend to show a relationship between an entity and the relationship. There is no provision for this in th
What's the difference between a primary key and a unique key? Both primary key and unique key enforces uniqueness of the column on which they are explained. But by default prim
Equi Join: A join in which the joining condition is based on equality among values in the common columns. Common columns show (redundantly) in the result table. Let us Consider th
Explain the conventions for displaying an ER schema as an ER diagram? An E-R Diagram scheme might describe certain constraints to that the contents of a database must conform.
Table_Name( attribute_1, attribute_2, attribute_3, ….. ,attribute_x) Primary Key ( attribute_1, attribute_2) Foreign Key attribute_4 References Table_Name_2 (repeat for each fore
what is natural join?
Example - ALTER TABLE emp MODIFY (empno NUMBER (7));
What is trigger? Triggers are statements that are executed automatically by the system as the side effect of a modification to the database.
Write short notes on data ware housing? Data ware housing applications needs the transformation of data from many sources into a cohesive reliable step set of data configured a
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