mysql - ON 语句中的别名是未知列

Question

我确定之前有人问过这个问题，但我没有找到答案。

在下面的 ON 语句中，我无法使用别名。 “on 子句”中的未知列“node__field_plant_descriptors.gid” (d_id会给出同样的错误)

SELECT descriptors.Entity_id AS d_id,
genus.field_plant_genus_value AS gval,
genus.Entity_id AS gid
FROM table__plant_descriptors AS descriptors
JOIN table__plant_genus AS genus 
ON genus.gid = descriptors.d_id /* HERE */
WHERE (field_1, field_2) 
IN ( (8758, 8109), (8770, 8060),(8773, 7922) ) 
GROUP BY Entity_id 
HAVING count(Entity_id) = 3

Answer 1

您不能直接通过名称访问别名。

as 创建一个列别名，您不能在列别名上加入。您可以在 ORDER BY 中使用别名，但不能在其他地方使用，除非别名来自子查询。

尝试下面的查询

    SELECT
  descriptors.Entity_id AS d_id,
  genus.field_plant_genus_value AS gval,
  genus.Entity_id AS gid
FROM
  table__plant_descriptors AS descriptors
  JOIN table__plant_genus AS genus ON table__plant_genus.gid = table__plant_descriptors.d_id
  /* HERE */
WHERE
  (field_1, field_2) IN ((8758, 8109), (8770, 8060),(8773, 7922))
GROUP BY
  Entity_id
HAVING
  count(Entity_id) = 3