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

问题描述

如何用JDBC检查结果集是否有一行或多行?

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，我们不需要行数，因为我们使用 WHILE 循环而不是 FOR 循环来迭代结果集:

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，您可能希望对结果进行窗口化，并且您需要提前记录计数以向用户显示类似 Row 1 to 10 of 100 的内容.您可以先使用 SELECT COUNT(*) 进行单独的查询，以获取记录计数，但请注意，该计数只是近似值，因为可以在执行所需的时间内添加或删除行两个查询.

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.

来自结果集概述的示例

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