MySQL查询将多列添加到3列

Question

我有以下mysql表和记录： http://sqlfiddle.com/#!9/fb7c68/1

我想创建一个将在3列中显示记录的查询

product_id, parent_option_id, parent_option_value_id (only if the parent_option_id > 0)
.
.
.
.
product_id, child_option_id, child_option_value_id (only if the child_option_id > 0)
.
.
.
.
product_id, grandchild_option_id, grandchild_option_value_id (only if the grandchild_option_id > 0)

Answer 1

如果我正确地理解了你想做什么，可以尝试用UNION组合的3个查询。

SELECT 
  product_id as id,
  parent_option_id as option_id, 
  parent_option_value_id as option_value_id 
FROM option_value
WHERE
  parent_option_id > 0
UNION
SELECT 
  product_id as id,
  child_option_id as option_id, 
  child_option_value_id as option_value_id
FROM option_value
WHERE
  child_option_id > 0
UNION
SELECT 
  product_id as id,
  grandchild_option_id as option_id, 
  grandchild_option_value_id as option_value_id
FROM option_value
WHERE
  grandchild_option_id > 0;