摘要：In some case, we found that when we execute the sql commands like truncate table, drop table, delete all records in table, join 2 tables, it will take 阅读全文

摘要：If a table have column A and B Count(distinct A) as Da Count(distinct B) as Db Count(distinct A, B) as Dab The Da/Db<=Dab, this will be always true; 1 阅读全文

摘要：If you don't have the permission to generate script according to an existing db, but you have the read permission for that db, if so you can use selec 阅读全文