在MySQL的官方手册上有这么一句话: the optimizer can estimate the row count for each range using dives into the index or index statistics. 这是在说: 优化器为每一个范围段(如“a IN (10, 20, 30)”包括2个范围段,一是10到20,二是20到30)估计这个范围段中包括的元组数, ...

I have two tables I'm doing a join with. Table1 has a PK on an id column which is Unique.<BR><BR>Table2 has a PK on two columns, uid,id which is Unique.<BR><BR>If I do a:<BR><BR>SELECT Table1.id, ...