不可预知的MySQL服务器行为左连接
CREATE TEMPORARY TABLE tmp_userid ( uUserId int unsigned NOT NULL PRIMARY KEY ) ENGINE='MEMORY'; CREATE TEMPORARY TABLE tmp_studentid ( uClassId INT UNSIGNED NOT NULL, uUserId int unsigned NOT NULL, PRIMARY KEY(uClassId,uUserId) ) ENGINE='MEMORY'; INSERT INTO tmp_userid values (18); INSERT INTO tmp_studentid values (1,1), (1,3), (2,15), (3,20), (3,25), (4,35), (4,45) ; 现在,如果我尝试执行: SELECT * FROM tmp_userid […]