如何检查结果集是否有一行或更多行？ [英] How to check if resultset has one row or more?

问题描述

如何检查结果集是否在JDBC中有一行或多行？

How to check if resultset has one row or more with JDBC?

推荐答案

ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM Table1");
boolean isMoreThanOneRow = rs.first() && rs.next();

你没有问这个，但你可能需要它：

You didn't ask this one, but you may need it:

boolean isEmpty = ! rs.first();

通常，我们不需要行计数，因为我们使用WHILE循环来迭代结果设置而不是FOR循环：

Normally, we don't need the row count because we use a WHILE loop to iterate through the result set instead of a FOR loop:

ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM Table1");
while (rs.next()) {
    // retrieve and print the values for the current row
    int i = rs.getInt("a");
    String s = rs.getString("b");
    float f = rs.getFloat("c");
    System.out.println("ROW = " + i + " " + s + " " + f);
}

但是，在某些情况下，您可能希望窗口显示结果，而您需要提前记录计数向用户显示类似第1行到第10行的100 。您可以先使用 SELECT COUNT（*）进行单独查询，以获取记录计数，但请注意，计数只是近似值，因为可以在两者之间添加或删除行执行两个查询所需的时间。

However, in some cases, you might want to window the results, and you need the record count ahead of time to display to the user something like Row 1 to 10 of 100. You can do a separate query with SELECT COUNT(*) first, to get the record count, but note that the count is only approximate, since rows can be added or removed between the time it takes to execute the two queries.

来自 ResultSet概述

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