Question

如何以相反的顺序从mysql数据库中每次选择2个数据。例如，在此表中

|---------------------|------------------|
|          id         |     category     |
|---------------------|------------------|
|          1          |         1        |
|---------------------|------------------|
|          2          |         3        |
|---------------------|------------------|
|          3          |         1        |
|---------------------|------------------|
|          4          |         2        |
|---------------------|------------------|
|          5          |         1        |
|---------------------|------------------|
|          6          |         3        |
|---------------------|------------------|
|          7          |         1        |
|---------------------|------------------|

我想在每次类别为1的情况下以相反的顺序选择2个数据。对于第一次运行查询，我将获得id = 7和id = 5的数据。对于第二次运行查询，我将获得id = 3和id = 1的数据。如何形成该查询？

Answer 1

您可以使用不同的（限制）查询：

select id from [your-table-name-here] where category=1 order by id desc limit 0, 2 --to get first two
select id from [your-table-name-here] where category=1 order by id desc limit 2, 2 --to get next two
...
select id from [your-table-name-here] where category=1 order by id desc limit x, x+2 --etc

Answer 2

除了SQL之外，您还希望使用其他语言来执行此操作。以下是使用PHP的示例：

$query_string = "SELECT `id` FROM `<TABLE NAME>` WHERE `category` = 1 ORDER BY `id` DESC";
$result = mysqli_query($link, $query_string); //where $link stores the connection to your MySQL database

if ($result != null) {

    $highest_id = mysqli_fetch_row($result)[0];

    $second_row = mysqli_fetch_row($result);

    if ($second_row != null) $second_highest_id = $second_row[0];
}

//etc

SQL如何以相反的顺序每次选择一定数量的数据

2 个答案: