Understanding SQL DDL and DML

What SQL command is used to modify an existing table structure?

• ALERT TABLE

• CREATE TABLE

• ALTER TABLE

• DROP TABLE

How do you define a primary key in a table?

• A primary key is an optional field in a table.

• A primary key is used to store large text data.

• A primary key is a unique identifier for a record in a table.

• A primary key can be duplicated across records.

What is the purpose of a foreign key in a relational database?

• To store data in a single table only.

• The purpose of a foreign key is to maintain referential integrity between related tables in a relational database.

• To increase the speed of data retrieval.

• To create a new table in the database.

Which SQL command is used to add constraints to a table?

• CREATE TABLE

• SELECT * FROM

• ALTER TABLE

• DROP TABLE

What happens to the data in a table when you use the TRUNCATE command?

• The table structure is removed but data remains.

• All data in the table is permanently removed.

• The data is temporarily hidden.

• Only specific rows are deleted.

Which of the following is auto-committed?

• INSERT

• UPDATE

• DROP

• DELETE

How can you enforce uniqueness on a column in a table?

• Use a FOREIGN KEY constraint on the column.

• Add a PRIMARY KEY to the table.

• Set the column to NULLABLE.

• Use a UNIQUE constraint on the column.

What SQL command would you use to remove a table from the database?

• ALTER TABLE table_name;

• DROP TABLE table_name;

• REMOVE TABLE table_name;

• DELETE TABLE table_name;

Can a table have multiple foreign keys?

• No, a table can only have one foreign key.

• No, foreign keys are not allowed in tables.

• Yes, a table can have multiple foreign keys.

• Yes, but only if the foreign keys reference the same table.

What is the effect of adding a NOT NULL constraint to a column?

• It automatically fills NULL values with a default value.

• It prevents NULL values from being stored in the column.

• It increases the storage size of the column.

• It allows NULL values to be stored in the column.