java - 查询时间慢 SQL/Java

Question

我正在查询一个包含数千行的相当大的数据库。它大约需要 5 分钟，而它应该需要大约 5 秒。

    ResultSet rs = st.executeQuery("SELECT flights.airline, flights.flight_num,"
            + "origin_airport_code, destination_airport_code,"
            + "ticket.date, ticket.bought_date, ticket.price "
            + "FROM flights JOIN flightinfo JOIN ticket");

我应该使用某种特定类型的连接 JOIN 语句吗？

Answer 1

目前，您的查询所做的是获取表的笛卡尔积，因为您尚未指定它们的连接条件或定义表之间的关联方式。

您需要在每个连接语句中添加一个条件或ON 子句，例如

SELECT  flights.airline, 
        flights.flight_num,
        origin_airport_code, 
        destination_airport_code,
        ticket.date, 
        ticket.bought_date, 
        ticket.price 
FROM    flights 
        INNER JOIN flightinfo 
            ON flights.colName = flightinfo.colname  -- << 1
        INNER JOIN ticket
            ON table.ColName = ticket.colName        -- << 2

地点:

1 >> Colname >> how the two tables:flights and flightinfo, are related
2 >> table >> I don't know where the table ticket will be joined, it is 
              either flights or flightinfo.

要进一步了解有关连接的更多信息，请访问以下链接:

• > Visual Representation of SQL Joins