SQL查询，用于返回连接到同一引用的多个字段

Question

So I have the following table, do_stock_movement, that looks like this:

stock_movement_id   sm_number   sm_source_id    sm_destination_id
15164b86a7533d           145    1516478840ee29  151644d8bd63f2
15166b89d1a9fc           194    15165c481bd9d0  151659e632cd48

The columns sm_source_id and sm_destination_id both reference product points stored in do_product_points .

I'm using the following SQL query:

SELECT * FROM do_stock_movement
INNER JOIN do_product_points ON product_points_id = sm_source_id
WHERE sm_number = '145'

In do_product_points , there's a field called pp_name . I need the corresponding pp_name for both sm_source_id and sm_destination_id .

However, the query above will only return the pp_name for sm_source_id , or for sm_destination_id if you change the joined field to that.

What SQL query will return the corresponding pp_name for both sm_source_id and sm_destination_id ?

I hope this is clear. Please ask questions if it isn't!

Answer 1

JOIN this table do_product_points one more times for the sm_destination_id :

SELECT 
  s.pp_name AS SourcePoint,
  d.pp_name AS DestinationPoint,
  ...
FROM do_stock_movement AS m
INNER JOIN do_product_points s ON s.product_points_id = m.sm_source_id
INNER JOIN do_product_points d ON d.product_points_id = m.sm_destination_id
WHERE m.sm_number = '145'

Answer 2

You need join twice and use alias:

SELECT *, Src.pp_name, Dst.pp_name FROM do_stock_movement
  INNER JOIN do_product_points as Src 
      ON Src.product_points_id = sm_source_id
  INNER JOIN do_product_points as Dst 
      ON Dst.product_points_id = sm_destination_id

Answer 3

You need to join to the product_points table twice, once with source_id and once with destination_id:

SELECT * FROM do_stock_movement move
INNER JOIN do_product_points source ON source.product_points_id = move.sm_source_id
INNER JOIN do_product_points dest ON dest.product_points_id = move.sm_destination_id
WHERE sm_number = '145'