Question

未知栏＆＃39; CURRENT_STOCK_LEVEL＆＃39;在＆＃39;字段列表＆＃39;

$queryString = 'SELECT A.ITEM_CODE, A.BEGINNING_BALANCE AS BEGINNING_BALANCE, B.DELIVERY AS DELIVERY, C.ISSUANCE AS ISSUANCE, 
(IFNULL(BEGINNING_BALANCE, 0) + IFNULL(DELIVERY, 0)) - IFNULL(ISSUANCE, 0) AS CURRENT_STOCK_LEVEL , A.REORDERPNT AS REORDERPNT,

IF( CURRENT_STOCK_LEVEL <= REORDERPNT, "LOW", "HIGH") AS STATUS

FROM MM_NEW_ROP_ITEMS AS A
LEFT OUTER JOIN (SELECT ITEM_CODE, SUM(QUANTITY) AS ISSUANCE FROM MM_NEW_ROP_ISSUANCES GROUP BY ITEM_CODE) AS C ON A.ITEM_CODE = C.ITEM_CODE
LEFT OUTER JOIN (SELECT ITEM_CODE, SUM(QUANTITY) AS DELIVERY FROM MM_NEW_ROP_DELIVERIES GROUP BY ITEM_CODE) AS B ON A.ITEM_CODE = B.ITEM_CODE
ORDER BY A.ITEM_CODE'; 

$query = mysql_query($queryString) or die(mysql_error());

//makes a loop and creates an array with query fields

$items = array();
while($item = mysql_fetch_assoc($query)) {
    $items[] = $item;
}

//encodes for JSON format
echo json_encode(array(
    "success" => mysql_errno() == 0,
    "items" => $items
));

Answer 1

这是您的SELECT：

SELECT A.ITEM_CODE, A.BEGINNING_BALANCE, B.DELIVERY AS DELIVERY, C.ISSUANCE, 
       (IFNULL(BEGINNING_BALANCE, 0) + IFNULL(DELIVERY, 0)) - IFNULL(ISSUANCE, 0) AS CURRENT_STOCK_LEVEL ,
       A.REORDERPNT AS REORDERPNT,
       IF(CURRENT_STOCK_LEVEL <= REORDERPNT, 'LOW', 'HIGH') AS STATUS

如错误所示，您无法在定义它的同一SELECT语句中重用列别名。这不仅适用于SELECT，也适用于查询的其他组成部分，例如WHERE。

所以，重复逻辑，我更喜欢COALESCE()和CASE（这是ANSI标准函数）：

SELECT A.ITEM_CODE, A.BEGINNING_BALANCE, B.DELIVERY AS DELIVERY, C.ISSUANCE, 
       (COALESCE(BEGINNING_BALANCE, 0) + COALESCE(DELIVERY, 0)) - COALESCE(ISSUANCE, 0)) AS CURRENT_STOCK_LEVEL ,
       A.REORDERPNT AS REORDERPNT,
       (CASE WHEN COALESCE(BEGINNING_BALANCE, 0) + COALESCE(DELIVERY, 0)) - 
                  COALESCE(ISSUANCE, 0) <= REORDERPNT
             THEN 'LOW' ELSE 'HIGH'
        END) AS STATUS

Answer 2

您可以使用MySQL会话变量来完成您的工作，而无需重复逻辑。

以下是在查询中执行此操作的方法：

SELECT A.ITEM_CODE, A.BEGINNING_BALANCE AS BEGINNING_BALANCE, B.DELIVERY AS DELIVERY, C.ISSUANCE AS ISSUANCE, 
    @temp_stock_level:=0, @temp_stock_level:=(IFNULL(BEGINNING_BALANCE, 0) + IFNULL(DELIVERY, 0)) - IFNULL(ISSUANCE, 0) AS CURRENT_STOCK_LEVEL , 
    A.REORDERPNT AS REORDERPNT,IF( @temp_stock_level <= REORDERPNT, "LOW", "HIGH") AS STATUS
    FROM MM_NEW_ROP_ITEMS AS A
    LEFT OUTER JOIN (SELECT ITEM_CODE, SUM(QUANTITY) AS ISSUANCE FROM MM_NEW_ROP_ISSUANCES GROUP BY ITEM_CODE) AS C ON A.ITEM_CODE = C.ITEM_CODE
    LEFT OUTER JOIN (SELECT ITEM_CODE, SUM(QUANTITY) AS DELIVERY FROM MM_NEW_ROP_DELIVERIES GROUP BY ITEM_CODE) AS B ON A.ITEM_CODE = B.ITEM_CODE
    ORDER BY A.ITEM_CODE;

在此查询中，我使用了@temp_stock_level变量来存储值CURRENT_STOCK_LEVEL

我如何在if语句中使用mysql别名列

2 个答案: