The order release table has more than 1000 ten thousand data, the relatively small PDA scan table, when the query order release full field, go indexes; When only query the order release one of the fields when a full table scan,

Why?

CodePudding user response:

Query field affect the size of the hash table, when the field is overmuch, overall performance will reduce the hash table is too high, the details is more complex to study

CodePudding user response:

Can be added on the second query use_hash prompt see, whether go to Hash join, in the case of HJ cost how much,

Can also directly in 10046, or dbms_xplan. Display_cursor look at the real execution plan of two SQL, see if consistent and F5,