Choose the SQL commands to perform following operations on a relation R:
I: Retain Relation R in database, but delete all tuples in R.
II: Delete all information about R in Database.

Question

Choose the SQL commands to perform following operations on a relation R: 
I: Retain Relation R in database, but delete all tuples in R. 
II: Delete all information about R in Database.

Accepted Answer

The correct option is (2):
This option correctly pairs the specific SQL commands with their defined functional behavior, which is a crucial concept in Database Management Systems. For operation I, "Retain Relation R in database, but delete all tuples in R," the correct DML (Data Manipulation Language) command is `DELETE FROM R`. This command selectively removes the data (rows/tuples) from the table while leaving the table's complete structure, including its schema, indexes, and constraints, perfectly intact within the database. For operation II, which requires the drastic action of permanently deleting "all information about R in Database," the correct DDL (Data Definition Language) command is `DROP TABLE R`. This command removes the entire table definition, including its structural metadata and all data, from the database catalog, making the table non-existent.

The incorrect option is (1):
Option 1 is incorrect because it reverses the intended functionality of the two commands. If we use `DROP TABLE R` for operation I, the relation R would not be retained; the entire table structure would be permanently erased, contradicting the instruction to "Retain Relation R." Using `DELETE FROM R` for operation II is also wrong because the table structure would remain, failing to delete "all information" about R. Therefore, this pairing does not satisfy the requirements of the question.

The incorrect option is (3):
This option presents syntactically incorrect or non-standard SQL commands for the required operations. The command to delete all rows is `DELETE FROM R`, while this option uses `DELETE TABLE R`, which is invalid syntax. Similarly, the correct command to remove the entire table is `DROP TABLE R`, while this option uses the incorrect syntax `DROP FROM R`. Since standard SQL does not recognize these commands for the intended purposes, executing them would result in a syntax error.

The incorrect option is (4):
The `ALTER TABLE` command is a DDL command used exclusively for *modifying* the structure of an existing table, such as adding, dropping, or modifying columns and constraints. It is not designed to delete all the data within a table (operation I) or to remove the entire table structure from the database (operation II). Furthermore, the syntax provided, "Alter R Drop," is incomplete and not a valid construct for either deleting tuples or permanently dropping a table.