Foundation studio

Start with the observation, not the syntax

In the movie exercise, one row describes a movie. In scripts, one row is a dialogue record. Rick can therefore appear in many rows. Before writing SQL, finish this sentence: “One row in this table represents …”. A familiar name does not make that name a unique identifier.

An id lets you return to the same source record. Selecting only characterName can produce repeated-looking rows even when the underlying records are different. Keep an identifier while investigating; remove it only when the requested report does not need it.

Columns, rows and values do different jobs

SELECT chooses output columns or expressions; FROM chooses the input table. SELECT characterName reads a stored value from each row. SELECT 'characterName' repeats a literal string instead. Both can execute, so an error-free query is not enough evidence of correctness.

Selecting fewer columns normally preserves the number of input rows. DISTINCT is a separate decision: it removes duplicate combinations of every selected value. Adding an id to a DISTINCT query can change its meaning because distinct records may share the same speaker.

Make the claim as narrow as the evidence

A six-row preview is useful for understanding structure. It does not establish the number of characters, the most important character, or the total amount spoken. Explain the result as “six dialogue records” until you have evidence for a broader statement.