Question

我创建了一个包含所有请求信息的请求表。

包含以下列的表：

requestid , itemrequest1, itemrequest2, itemrequest3, quantity1, quantity2, quantity3

如何建立关系，以便如果itemrequest在itemrequest2列中有值，则会从列quantity2中获取数量。

我的查询是这样的：

$query2=mysql_query("select * from tbl_request WHERE unit='$unit' AND  (itemrequest1='$itemrequest' or itemrequest2='$itemrequest' or  itemrequest3='$itemrequest')");
$record_num=mysql_num_rows($query2);

while ($data1 = mysql_fetch_array($query2))

问题是当$itemrequest列itemrequest3中有值时，数量将始终显示第1列的数量。

Answer 1

You can use conditions in your query in order to select the right column depending on another column's value.

SELECT requestid, 
    (CASE WHEN itemrequest1 = '$itemrequest' THEN quantity1
        ELSE (
            CASE WHEN itemrequest2 = '$itemrequest' THEN quantity2
            ELSE (
                CASE WHEN itemrequest3 = '$itemrequest' THEN quantity3
            END)
        END)
    END)
FROM tbl_request

You should have a close look to your database structure though, if you have to do things like this, it might be better to improve your structure and have better tables/fields.

如何在PHP MYSQL中关联两列

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