Which pattern is not permitted when combining data joins with column selection?

• A. A join and Select * together
• B. A join with explicit column list
• C. A query without a join
• D. A query that uses an aggregate function

Answer: (A)

When combining data joins with column selection, you must specify exactly which columns to return rather than using a wildcard. Selecting all columns with a join isn’t supported because joined tables can have overlapping or ambiguous column names and the system needs a clear output schema. You can join and explicitly name the columns you want from each table, you can run queries that don’t use a join, and you can include aggregate functions as part of your select (with proper grouping). So the pattern that isn’t allowed is using a join together with SELECT *.