根據mysql中的不同條件選擇兩列

Question

<?php
    $inventory_in = $db->get_one("SELECT COALESCE(SUM(Qty), 0) 
                    FROM inventory Where id=12 AND inv_type = 'in' LIMIT 1");

    $inventory_out = $db->get_one("SELECT COALESCE(SUM(Qty), 0) 
                     FROM inventory Where id=12 AND inv_type = 'out' LIMIT 1");

    $inventory = $inventory_in - $inventory_out;
?>

可以將兩個查詢合並為一個嗎？

謝謝。

Answer 1

假設您想要兩個值輸出，您可以使用SUM / CASE

SELECT
      COALESCE(SUM(CASE WHEN inv_type = 'in' THEN Qty ELSE 0 END ), 0) as  Sum1,
      COALESCE(SUM(CASE WHEN inv_type = 'out' THEN Qty ELSE 0 END ), 0) as  Sum2
FROM inventory 
WHERE id=12 
LIMIT 1

您可能希望將and inv_type in ('in', 'out')添加到where子句中，但不是必需的。

Answer 2

有條件的金額怎么樣？

SELECT 
    SUM(CASE WHEN inv_type = 'in' THEN 1 ELSE 0 END) InSum
    SUM(CASE WHEN inv_type = 'out' THEN 1 ELSE 0 END) OutSum
WHERE
    id = 12

或者，如果你只是想要結果

SELECT 
    SUM(CASE inv_type WHEN 'in' THEN 1 WHEN 'out' THEN -1 ELSE 0 END) TotalSum
WHERE
    id = 12

Answer 3

SELECT inv_type, COALESCE(SUM(Qty), 0) 
FROM inventory
WHERE id=12 AND inv_type IN ('in', 'out')
GROUP BY inv_type