有个SQL问题，请教众大佬。。。
有个数据表有联合索引index（id1，id2）， ①explain select * from test where id1=1 and id2=1; ②explain select * from test where id1=1 or id2=1; ③explain select * from test where id1<3 and id2=1; ④explain select * from test where id1=1 and id2<2; 哪些用到了该index，如何运行的呢？
