mysql - Select Some of Two columns based on another table

Question

I have two tables

Joined_courses_table

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id      course1_id   course2_id
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1           33           3
2           2            1

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Results_table

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course_id    value
---------------------------------------
33             50
3              40
2              70
1              130
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Problem -> I want the Values Sum from results_table for each two pairs in the Joined_courses_table

Answer 1

尝试这个：

SELECT
  id, course1_id, course2_id, 
  results1.value + results2.value AS values_sum
FROM
  Joined_courses_table
  JOIN Results_table results1 ON (course1_id = results1.course_id)
  JOIN Results_table results2 ON (course2_id = results2.course_id)

如果您有一个PRIMARY KEYon ，查询应该执行良好Results_table.course_id。