select * from T_HOGE where CARDID = (select CARDID from T_FUGA where FLG<>"0")
[21000][1242] Subquery returns more than 1 row
副問い合わせでよくあるエラー
https://dev.mysql.com/doc/refman/5.0/en/subquery-errors.html
select * from T_HOGE where CARDID = any (select CARDID from T_FUGA where FLG<>"0")
ANY を使う。 (IN節みたいなもの)