Question

我有一个名为Location_ID |Item_ID |Stock 1 |A |100 1 |B |500 1 |C |300 2 |A |10 2 |B |20的表，结构如下：

location_ID

字段item_ID和Item_ID |Stock_1 |Stock_2 A |100 |10 B |500 |20 C |300 |0是复合键。我想从该单个表中生成以下数据：

Item_ID

我尝试编写了几个自联接查询，但它不起作用。还有另一个问题：location_ID上{{1}} C不存在.2。我们如何设置值＆＃39; 0＆＃39; 0在结果表上，如果它不存在？有聪明才智的人可以放弃任何光明吗？

Answer 1

select DIS_ITME_ID,
       IFNULL ((select stock
                 from inventory
                where location_id = 1
                  and item_id = DIS_ITEM_ID), 0) as stock_1,
       IFNULL ((select stock
                 from inventory
                where location_id = 2
                  and item_id = DIS_ITEM_ID), 0) as stock_2
  from (select distinct item_ID as DIS_ITEM_ID from inventory)

Answer 2

我知道这可能为时已晚，但有一种更简单的方法：

SELECT Item_Id,
       SUM(
       CASE WHEN Location_ID = 1 THEN
         Stock
       ELSE 
          0 
       END) As Stock1,
       SUM(
       CASE WHEN Location_ID = 2 THEN
         Stock
       ELSE 
          0 
       END) As Stock2
FROM Inventory
GROUP BY Item_Id

sqlfiddle

Answer 3

您可以使用dinamic pivot查询：

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'SUM(IF(i.location_ID = ''',
      CAST(location_ID as CHAR(50)),
      ''', i.stock, 0)) AS stock_',
      CAST(location_ID as CHAR(50))
    )
  ) INTO @sql
FROM inventory;
SET @sql = CONCAT('SELECT i.item_ID, ', @sql, ' 
                   FROM inventory i
                   GROUP BY i.item_ID');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

您可以在此处找到更多信息：http://buysql.com/mysql/14-how-to-automate-pivot-tables.html

MySQL自联接表

3 个答案: