[英]Selecting ambiguous column from subquery
Suppose we have the following query: 假设我们有以下查询:
select c.a, c.b, c.d
from
(select * from
tab1 join tab2
on tab1.id = tab2.id)c
I get the following error: ERROR: 42702: column reference "d" is ambiguous
我收到以下错误: ERROR: 42702: column reference "d" is ambiguous
How would I fix this? 我该如何解决? Can I do something like c.tab1.id
? 我可以做类似c.tab1.id
事情吗?
You may write your query like: 您可以这样写查询:
SELECT a, b, d FROM (SELECT tab1.a AS a, tab1.b AS b, tab2.c AS c, tab2.d AS d
FROM tab1 JOIN tab2 ON tab1.id = tab2.id)c;
The error is happening because both tab1
and tab2
have a column called d
. 发生错误是因为tab1
和tab2
都有一个名为d
的列。
The simplest solution is to eliminate the subquery: 最简单的解决方案是消除子查询:
select ?.a, ?.b, ?.d
from tab1 join
tab2
on tab1.id = tab2.id
The ?
?
is a placeholder for the table where the column comes from. 是列来源表格的占位符。
If you need the subquery, then you should similarly use qualified column names instead of select *
, so you identify where the columns are coming from. 如果需要子查询,则应类似地使用限定的列名,而不要使用select *
,以便确定列的来源。
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