sql - 多表内连接

Question

我有这四个表:

PRODUCTS
---------
PRODUCT_ID
PRODUCT_TITLE
(other fields)

COLORS
---------
COLOR_ID
COLOR_NAME

MATERIALS
---------
MATERIAL_ID
MATERIAL_NAME

IMAGES
---------
IMAGE_ID
BIG
MED
SMALL
THUMB

SIZE
---------
SIZE_ID
SIZE_NAME

并且:

PRODUCT_COLOR
---------
PRODUCT_ID
COLOR_ID

PRODUCT_MATERIAL
---------
PRODUCT_ID
MATERIAL_ID

PRODUCT_SIZE
---------
PRODUCT_ID
SIZE_ID

PRODUCT_IMAGE
---------
PRODUCT_ID
IMAGE_ID
COLOR_ID (can be null)
MATERIAL_ID (can be null)

所有产品都可以有不同的颜色和/或 Material 。例如。我可以拥有一种产品，它具有一种或多种 Material 选项，但没有相关联的颜色，反之亦然。输出应该是这样的:

-----------------------------------------------------------------------------
| PRODUCT_ID | PRODUCT_NAME  | COLOR_ID | MATERIAL_ID | IMAGE_ID | SIZE_ID |
-----------------------------------------------------------------------------
| 1          | T-SHIRT       | 1        | null        | 1        | 1        |
| 1          | T-SHIRT       | 1        | null        | 1        | 2        |
| 1          | T-SHIRT       | 1        | null        | 1        | 3        |
| 1          | T-SHIRT       | 1        | null        | 1        | 4        |
| 2          | JEANS         | null     | 1           | 2        | 1        |
| 2          | JEANS         | null     | 1           | 2        | 2        |
| 2          | JEANS         | null     | 1           | 2        | 3        |
| 2          | JEANS         | null     | 1           | 2        | 4        |
| 2          | JEANS         | null     | 1           | 2        | 5        |
| 3          | T-SHIRT VNECK | 2        | 2           | 3        | 1        |
| 3          | T-SHIRT VNECK | 2        | 2           | 3        | 2        |
| 3          | T-SHIRT VNECK | 3        | 2           | 4        | 1        |
| 3          | T-SHIRT VNECK | 3        | 2           | 4        | 2        |
| 3          | T-SHIRT VNECK | 4        | 3           | 5        | 1        |
| 3          | T-SHIRT VNECK | 4        | 3           | 5        | 2        |
-----------------------------------------------------------------------------

我尝试了以下语句，但它返回 0 行:

SELECT PRODUCTS.PRODUCT_ID, PRODUCTS.PRODUCT_TITLE, COLORS.COLOR_ID, MATERIALS.MATERIAL_ID, IMAGES.IMAGE_ID, SIZE.SIZE_ID from PRODUCTS
    INNER JOIN PRODUCT_COLOR ON (PRODUCTS.PRODUCT_ID = PRODUCT_COLOR.PRODUCT_ID)
    INNER JOIN COLORS ON (COLORS.COLOR_ID = PRODUCT_COLOR.COLOR_ID)
    INNER JOIN PRODUCT_MATERIAL ON (PRODUCTS.PRODUCT_ID = PRODUCT_MATERIAL.PRODUCT_ID)
    INNER JOIN MATERIALS ON (MATERIALS.MATERIAL_ID = PRODUCT_MATERIAL.MATERIAL_ID)
    INNER JOIN PRODUCT_IMAGE ON (PRODUCTS.PRODUCT_ID = PRODUCT_IMAGE.PRODUCT_ID)
    INNER JOIN IMAGES ON (IMAGES.IMAGE_ID = PRODUCT_IMAGE.IMAGE_ID)
    INNER JOIN PRODUCT_SIZE ON (PRODUCTS.PRODUCT_ID = PRODUCT_SIZE.PRODUCT_ID)
    INNER JOIN SIZE ON (SIZE.SIZE_ID = PRODUCT_SIZE.SIZE_ID)
    ORDER BY PRODUCTS.id_PRODUCT;

有任何想法吗？

Answer 1

你可以这样做:

select p.product_id,
  p.product_name,
  c.color_id,
  m.material_id,
  i.image_id,
  s.size_id
from products p
left join product_color pc
  on p.product_id = pc.product_id
left join colors c
  on pc.color_id = c.colorid
left join product_material pm
  on p.product_id = pm.product_id
left join materials m
  on pm.material_id = m.material_id
left join product_image pi
  on p.product_id = pi.product_id
left join images i
  on pi.image_id = i.image_id
  or c.color_id = i.color_id
  or m.material_id = i.material_id
left join product_size ps
  on p.product_id = ps.product_id
left join size s
  on ps.size_id = s.size_id

我建议您查看 JOIN s。有一个很棒的 visual explanation of joins在线将帮助您编写这些查询。