MySQL:分组

Question

我想按 m.ID 分组，并对每个 m.id 求和 (pm.amount_construction* prod.anzahl)

实际上我有以下结果:

Meterial_id | amount_construction | Anzahl_der_productionen | Total_amount
---------------------------------------------------------------------------
181         | 1                   | 10                      | 10
181         | 2                   | 20                      | 40
181         | 1                   | 100                     | 100
182         | 1                   | 10                      | 10
182         | 1                   | 20                      | 20
183         | 1                   | 100                     | 100
283         | 1                   | 5                       | 5
283         | 1                   | 10                      | 10
283         | 2                   | 100                     | 200
283         | 10                  | 55                      | 550

What I need is the following (column 2 and 3 are not necessary)

Meterial_id | Total_amount
---------------------------
181         | 150
182         | 30 
183         | 100
283         | 765

I tried Group By m.id and did sum(pm.amount_construction * prod.anzahl) but I got strange results

Please see my code below:

SELECT
m.id As Meterial_id,    
pm.amount_construction AS amount_construction,    
prod.anzahl as Anzahl_der_productionen,    
(pm.amount_construction* prod.anzahl) as Total_amount

FROM produktion prod
JOIN projekt p    
   ON prod.projekt = p.id
JOIN kunden k    
   ON k.id = p.kunde
   LEFT JOIN bauteil b    
      ON b.produktion = prod.id    
JOIN product_material pm
JOIN material m    
   ON m.id = pm.material_id
JOIN product_configurationelement pce    
   ON pce.id = pm.product_configurationelement_id    
JOIN product_configurationelement_value pcev    
   ON pcev.product_configurationelement_id = pm.product_configurationelement_id    
   AND pcev.value_nr = pm.value_nr
JOIN product_type  pt
JOIN produkt pd
   ON pd.id = prod.produkt
JOIN product_generation pg
   ON pg.product_type_id = pt.id
JOIN product_modification pmm
   ON pmm.product_generation_id = pg.id
WHERE (prod.anzahl > 0 and pt.id = pd.product_type_id AND pm.product_generation_id = pd.product_generation_id  AND pg.generation = pd.generation AND p.starttermin <= '2018-07-05')    
ORDER BY m.id

Answer 1

许多加入。其中一些无效。 JOIN 是 INNER JOIN 的缩写，需要一个 ON 或 USING 子句。然而，当您忘记该子句时，MySQL 会默默地将 JOIN 转换为 CROSS JOIN。然后可能会导致可怕的错误，但是您在 WHERE 子句中隐藏了条件，因此据我所知，所有表似乎都已正确连接。

无论如何，很多连接是没有必要的。例如，为什么加入 bauteil？每个produktion 可以有很多bauteil，因此您将结果乘以bauteil 的数量。我猜与 product_configurationelement、product_configurationelement_value、product_generation 和 product_modification 相同。然后是 kunden、produkt 等多余的连接。

如果我没记错的话，这应该是您需要的:所有 product_material 与 produktion 结合，项目匹配日期范围，按 material_id< 分组 为每种 Material 获取一个结果行。

SELECT
  pm.material_id,    
  SUM(pm.amount_construction * produktion.anzahl) as total_amount
FROM product_material pm
JOIN produkt p ON p.product_generation_id = pm.product_generation_id
JOIN produktion ON produktion.produkt = p.id and produktion.anzahl > 0
WHERE produktion.projekt IN (SELECT id FROM projekt WHERE starttermin <= date '2018-07-05')
GROUP BY pm.material_id
ORDER BY pm.material_id;