Question: Show the ids of the investors who have at least two transactions.
Schema: create table transactions (investor_id varchar, PRIMARY KEY (investor_id)); create table investors (investor_id varchar, PRIMARY KEY (investor_id))
SQL: select t2.investor_id from investors as t1 join transactions as t2 on t1.investor_id = t2.investor_id group by t2.investor_id having count(*) >= 2