Which of the following SQL queries deletes all tuples in the teacher relation…

A DELETE statement's WHERE clause can only test columns belonging to the table it deletes from. When the filtering condition instead depends on an attribute stored in a DIFFERENT relation, the standard, portable way to express this is a subquery: first resolve the qualifying values from that other relation, then match the outer DELETE's WHERE...IN clause against the resulting set. (Some dialects also allow a correlated EXISTS or a joined DELETE/USING form for the same logic, but the subquery form is the one offered here.)

1. The inner subquery, SELECT dept_name FROM department WHERE building = 'CSE', resolves to the set of department names whose department is located in the CSE building.

2. The outer query, DELETE FROM teacher WHERE dept_name IN (...), then removes every teacher row whose dept_name is a member of that resolved set -- this is the query that satisfies the requirement.

Checking why every other option fails:

• A query that compares dept_name directly to the building's name 'CSE' mixes two different attributes from two different relations, and is not a syntactically valid IN condition either way.

• A query that deletes rows from the department relation itself removes department records, not the associated teacher records the question asks for.

• Since a valid query does satisfy the requirement, the option stating that none of the given queries works does not hold.

The subquery-based DELETE is therefore the query, among those offered, that correctly performs the required deletion.