Almost anyone who has spent time working with SQL made — or had to fix — this kind of bug:
-- two tables (sketch)
--
users {id, user_name}
trans {id, amt, cur, tx_time, user_id}
-- query with a typo
--
SELECT user_name
, tx_time
, amt
, cur
FROM users as u
JOIN trans as t ON u.id = t.id -- <- typo !!
WHERE user_name = 'jack' ;
Try the query, here is the DDL with some data; note the wrong result. Continue reading "Types and Typos in SQL [1]"