Question

我有这样的查询。

SELECT col1,
       (SELECT another_col1 FROM table1 WHERE table1.date = col1) AS some_col
FROM table1
ORDER BY id;

但是我不能在子查询中使用 col1 ，它总是返回最后一条记录但不匹配。

如何在PostgreSQL中使用它？

Answer 1

你应该为表格添加别名！除非您要比较的列是唯一的，否则优化程序将采用当前级别的每一列E.G. - 如果要在相关查询中进行比较，并且内部表与外部表具有相同的列名，则优化器会认为您需要比较内部表中的列。

SELECT t.col1,
      (SELECT s.another_col1 FROM Table1 s WHERE s.date = t.col1) as some_col
FROM table1 t
ORDER BY t.id

Answer 2

使用此

SELECT (SELECT another_col1 FROM table1 WHERE table1.date = col1) as
 col1,(SELECT another_col1 FROM table1 WHERE table1.date = col1) AS
 some_col FROM (select col1 as col1 from table1) as col1 ORDER BY id;

如何使用专栏＆＃39;子查询中的值？

2 个答案: