使用不同的参数多次运行相同的选择查询:Mysql [英] Running the same select query multiple times with different parameters: Mysql

问题描述

我有一个Java程序，该程序需要遍历HashMap以获得用于查询MySQL数据库的参数.

I have a java program that needs to iterate through a HashMap to get a parameters that are then used to query the MySQL database.

代码如下:

Iterator<Entry<String, Double>>it = ws.entrySet().iterator();
Connection con = null;

while(it.hasNext())  
{
    Entry<String, Double>pairs = it.next();
    PreparedStatement ps = con.prepareStatement("select doc_freq from lookup where word=?");
    ps.setString(1, pairs.getKey());
    ResultSet rs = ps.executeQuery();
}

针对循环的每次迭代(大约500次)重复访问数据库的过程使我的应用程序变慢.有什么办法可以一次发送所有这些参数，以便我只能访问一次数据库?

The process of repeatedly accessing the database for every iteration of the loop (which is about 500 times) is slowing down my application. Is there any way I can send all these parameters at once so that i access the database only once?

推荐答案

考虑到ws是一张地图，您可以通过以下方式进行单个查询:

Considering ws is a map, you can do a single query that way:

Connection con = getConnection();
Set<String> ks = ws.keySet();

if (ks.size() > 0) {
    StringBuilder inStatement = new StringBuilder("?");
    for (int i = 1; i < ks.size(); i++) {
        inStatement.append(", ?");
    }

    PreparedStatement ps = con.prepareStatement("select doc_freq from lookup where word in (" + inStatement.toString() + ")");

    int k = 1;
    for (String key : keySet) {
        ps.setString(k++, key);
    }
    ResultSet rs = ps.executeQuery();
}

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