17. The method according to claim 2 , before obtaining a first query plan and a second query plan for the query request, further comprising: evaluating a hash join query plan that uses a hash join operation and a sort merge join query plan that uses a sort merge join operation for the second query plan based on a cost model in a database query engine optimizer; and selecting one of the hash join query plan or the sort merge join query plan which requires a smaller cost, as the second query plan.
2. A method of database query, comprising: in response to a query request, obtaining a first query plan for minimum query, response time and a second query plan for minimum query total time for the query request; starting execution of the first query plan and execution of the second query plan at substantially a same time; outputting, before execution of the second query plan reaches a specified point, an initial query result obtained from execution of the first query plan; and in response to execution of the second query plan reaching the specified point, continuing execution of the second query plan to output remaining query results, wherein the first query plan is a query plan using a nested loop join operation, the second query plan is a query plan using a sort merge and the specified point is a point where a construction stage of the sort merge loin operation ends, wherein in the construction stage of the sort merge join operation, another table which is not a driving table of the first query plan is sorted according to a join column to obtain a sorted table of the another table, and wherein continuing execution of the second query plan comprises: performing no operation of an execution stage of the second query plan using the sort merge join on records already subjected to the nested loop join operation of the first query plan in the driving table of the first query plan.