Optimize the query (work in progress)

Scenario: Double-table joint query cannot be used, only by querying a single table, the query result can be used as the query condition of the second table.

Solution: First of all, it must be clear that java establishes query connections with the database many times, and the query will consume a lot of time. What optimization needs to be done is to reduce the time, so that the number of times that java establishes a connection with the database for query can be reduced.time.

Idea 1 (unoptimized): traverse the found data in Table 1, obtain the attributes required by the corresponding Table 2 during the traversal, and directly query it in Table 2 to obtain the results of Table 2 until the traversal ends.

Idea 2 (optimization): Find the data in Table 1, then put the data in Table 1 that needs to be used in Table 2 into the collection, and then query in Table 2 according to the data in the collection, and then inFilter the found data according to the conditional attributes to get the desired data.

It may be a bit laborious to say this, but the idea of ​​optimization is to reduce the number of connections to the database, because this connection is time-consuming. Through the algorithm, the data range is too large by reducing the number of connections before.desired data.