Select the SQL query expression(s) that have completely valid syntax when grouping and...

In standard SQL, any column in the SELECT list that is not part of an aggregate function must be included in the GROUP BY clause. Option A correctly groups by customer_id and uses an aggregate function in both the SELECT and HAVING clauses, which is syntactically valid.

Step-by-step Derivation:
Step 1: Analyze Option A: SELECT customer_id, MAX(is_active) FROM transactions GROUP BY customer_id HAVING MAX(is_active). The non-aggregated column customer_id is in the GROUP BY clause. The HAVING clause uses an aggregate function MAX(is_active). In many SQL dialects (like PostgreSQL or MySQL), a boolean or numeric result in the HAVING clause is treated as a predicate. This is syntactically valid.

Step 2: Analyze Option B: SELECT customer_id, is_active FROM transactions GROUP BY customer_id HAVING MAX(is_active). This is invalid because is_active is in the SELECT list but is neither aggregated nor present in the GROUP BY clause.

Step 3: Analyze Option C: SELECT customer_id, DISTINCT is_active FROM transactions GROUP BY customer_id HAVING MAX(is_active). This is invalid because DISTINCT is a keyword that applies to the entire row set in the SELECT clause (e.g., SELECT DISTINCT ...), not to a specific column within a list of other columns.

Step 4: Analyze Option D: SELECT customer_id, MAX(is_active) AS is_active FROM transactions GROUP BY customer_id HAVING is_active. This is invalid in standard SQL because the HAVING clause is processed before the SELECT alias is defined; therefore, it cannot refer to the alias is_active to represent the aggregate result.