如何从一个表中获取 select 条记录，其中第二个表的一列中所有记录的值与第一个表的多个列中的任何一个相匹配？

Question

There is a table (table A) with columns parent1, parent2..., parent7. All these columns contain user_id values, showing user_id values of 7 generations. Now there is another table (table B) which contains a column of some user_id values. I want to select all the records from table A which contain any of the user_db values from table B in any of table A's parent columns. How do I do that?

Answer 1

Table joins is the way to do this.

SELECT a.*
FROM table_a a
JOIN table_b b ON (
  a.parent1=b.user_id
  OR a.parent2=b.user_id
  OR a.parent3=b.user_id
  OR a.parent4=b.user_id
  OR a.parent5=b.user_id
  OR a.parent6=b.user_id
  OR a.parent7=b.user_id
)