Question 1

What does SQL stand for?

Accepted Answer

Structured Query Language. SQL stands for Structured Query Language — the standard language for interacting with relational databases.

Question 2

Which SQL command is used to retrieve data from a table?

Accepted Answer

SELECT. SELECT is the SQL command used to query and retrieve data. It is the most frequently used SQL command.

Question 3

What is a primary key in a database table?

Accepted Answer

A unique identifier for each row. A primary key uniquely identifies each row. It must be unique and cannot be NULL. A table can have only one primary key.

Question 4

Which SQL clause is used to filter rows based on a condition?

Accepted Answer

WHERE. WHERE filters rows before any grouping. HAVING filters after GROUP BY. ORDER BY sorts results. WHERE is the standard row-level filter.

Question 5

What does NULL represent in SQL?

Accepted Answer

The absence of a value — unknown or missing. NULL means no value has been assigned. NULL ≠ 0 and NULL ≠ '' (empty string). Any comparison with NULL returns NULL, not true or false.

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