Question

which operation is used to extract specific columns from a table?

Answer 1

The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.
SQL SELECT Syntax
SELECT column_name,  (This query will give you one particular column)
FROM table_name;
And
SELECT * FROM table_name; (This will give you all column)

Comments

And Project Operation in relational algebra is equivalent to Select operation of SQL.

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Analogous not equivalent to be specific