Sql Interview Question and Answers:
7. Define Primary Key?
The primary key is the columns used to uniquely identify each row of a table.
A table can have only one primary key.
No primary key value can appear in more than one row in the table.
8. Define Unique Key?
Unique key is a one or more column that must be unique for each row of the table.
It is similar to primary key. Primary key column will not accept a null. Whereas the unique key column will accept a null values.
9. Define Foreign Key?
A foreign Key is a combination of columns with value is based on the primary key values from another table. A foreign key constraint also known as Referential Integrity Constraint.
10. Define View?
A View is a database object that is a logical representation of a table.
It is derived from a table but has no longer of its own and often may be used in the same manner as a table.
A view is a virtual table that has columns similar to a table.
A view does not represent any physical data.
11. Compare and contrast TRUNCATE and DELETE for a table?
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.
12. What is cursors?
Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.
7. Define Primary Key?
The primary key is the columns used to uniquely identify each row of a table.
A table can have only one primary key.
No primary key value can appear in more than one row in the table.
8. Define Unique Key?
Unique key is a one or more column that must be unique for each row of the table.
It is similar to primary key. Primary key column will not accept a null. Whereas the unique key column will accept a null values.
9. Define Foreign Key?
A foreign Key is a combination of columns with value is based on the primary key values from another table. A foreign key constraint also known as Referential Integrity Constraint.
10. Define View?
A View is a database object that is a logical representation of a table.
It is derived from a table but has no longer of its own and often may be used in the same manner as a table.
A view is a virtual table that has columns similar to a table.
A view does not represent any physical data.
11. Compare and contrast TRUNCATE and DELETE for a table?
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.
12. What is cursors?
Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.
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