MySQL的多級子查詢

Question

我嘗試使用從連接表「glpi_items_tickets」字段成這樣子查詢：

SELECT 
     NAME 
    FROM 
     (
      SELECT 
       NAME 
      FROM glpi_computers 
      WHERE id = git.items_id 
     ) AS t1 
    UNION 
     (
      SELECT 
       NAME 
      FROM glpi_monitors 
      WHERE id = git.items_id 
     ) 
    UNION 
     (
      SELECT 
       NAME 
      FROM glpi_networkequipments 
      WHERE id = git.items_id 
     ) 
    UNION 
     (
      SELECT 
       NAME 
      FROM glpi_printers 
      WHERE id = git.items_id 
     ) 
) AS aliasIT 

，但我有類型的錯誤：「＃1054 - 未知列「git.items_id 「在where子句」

將整個request：

SELECT 
    gt.id, 
    (
     SELECT 
      NAME 
     FROM 
      (
       SELECT 
        NAME 
       FROM glpi_computers 
       WHERE id = git.items_id 
      ) AS t1 
     UNION 
      (
       SELECT 
        NAME 
       FROM glpi_monitors 
       WHERE id = git.items_id 
      ) 
     UNION 
      (
       SELECT 
        NAME 
       FROM glpi_networkequipments 
       WHERE id = git.items_id 
      ) 
     UNION 
      (
       SELECT 
        NAME 
       FROM glpi_printers 
       WHERE id = git.items_id 
      ) 
    ) AS aliasIT 
FROM glpi_tickets gt 
INNER JOIN glpi_items_tickets git 
ON gt.id = git.tickets_id; 

你有應用的領域中的解決方案‘glpi_items_tickets.items_id’到我的子查詢？

Answer 1

SELECT ... 
FROM 
    glpi_tickets gt 
    INNER JOIN glpi_items_tickets git 
     ON git.tickets_id = gt.id; 
    INNER JOIN 
    (
     SELECT NAME, id FROM glpi_computers 
     UNION 
     SELECT NAME, id FROM glpi_monitors 
     UNION 
     SELECT NAME, id FROM glpi_networkequipments 
     UNION 
     SELECT NAME, id FROM glpi_printers 
    ) g 
     ON g.id = git.items_id 

Answer 2

使用全表名稱而不是別名。

每git.items_id更換爲glpi_items_tickets.items_id。

在編譯子查詢期間，別名不存在，因爲外部查詢（您設置別名的地方）不能編譯，直到內部查詢被認爲是有效的。