CREATE TABLE TRANSACTIONS (investor_id VARCHAR)
CREATE TABLE INVESTORS (Investor_details VARCHAR, investor_id VARCHAR)

Show the id and details of the investor that has the largest number of transactions.
SELECT T2.investor_id, T1.Investor_details FROM INVESTORS AS T1 JOIN TRANSACTIONS AS T2 ON T1.investor_id = T2.investor_id GROUP BY T2.investor_id ORDER BY COUNT(*) DESC LIMIT 1
SELECT "T2"."investor_id", "T1"."Investor_details" FROM "INVESTORS" AS "T1" JOIN "TRANSACTIONS" AS "T2" ON "T1"."investor_id" = "T2"."investor_id" GROUP BY "T2"."investor_id" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1