SELECT * FROM
(
SELECT '1' AS ID FROM DUAL UNION ALL
SELECT '2' AS ID FROM DUAL UNION ALL
SELECT '3' AS ID FROM DUAL UNION ALL
SELECT '4' AS ID FROM DUAL UNION ALL
SELECT '2' AS ID FROM DUAL UNION ALL
SELECT '4' AS ID FROM DUAL
) T1 LEFT JOIN UER T2 ON T1.ID=T2.ID
如果都要显示,你就只能造一张ID的临时表作为左表,去left join uer表