php - 为什么这是模棱两可的？

Question

当我查询时:

$result = pg_query($dbconn, 
"SELECT w_bildurl, 
w_homepage_package_id AS whpi                         

FROM adempiere.w_homepage_package                           
LEFT JOIN adempiere.w_homepage_image ON adempiere.w_homepage_package.w_homepage_package_id = adempiere.w_homepage_image.w_homepage_package_id
LEFT JOIN adempiere.w_bilder ON adempiere.w_homepage_image.w_bilder_id = adempiere.w_bilder.w_bilder_id
WHERE sequence > 0
ORDER BY sequence ASC");

我明白了

 Query failed: ERROR: column reference 
"w_homepage_package_id" is ambiguous LINE 1:
 SELECT w_bildurl, w_homepage_package_id AS whpi

我认为将别名添加到 w_homepage_package_id 可以防止歧义。我是否必须将别名添加到 LEFT JOIN 或如何从查询中获取 w_homepage_package_id？

Answer 1

由于同一列在多个表中，因此需要在前面加上表别名，因此更改如下

SELECT tablealis.w_bildurl, 
tablealias.w_homepage_package_id AS whpi     

只需将 tablealias 更改为这些列所属表的实际表别名