Jak mogę użyć mysql alias kolumna w instrukcja if - php, mysql, alias

Nieznana kolumna "CURRENT_STOCK_LEVEL" w "liście pól"

$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
));

Odpowiedzi:

To jest twoje 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

Jak sugeruje błąd, nie można ponownie użyć aliasu kolumny w tym samym SELECT oświadczenie, w którym jest zdefiniowane. Dotyczy to nie tylko SELECT, ale także do innych elementów zapytania, takich jak WHERE.

Powtarzaj więc logikę i wolę COALESCE() i CASE (jest to standardowa funkcja ANSI):

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

Możesz używać zmiennych sesji MySQL, które wykonują zadanie bez powtarzania logiki.

Oto sposób, aby to zrobić w zapytaniu:

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;

W tym zapytaniu użyłem zmiennej @temp_stock_level do przechowywania wartości CURRENT_STOCK_LEVEL