爲什麼不能識別選擇部分中命名的別名？

Question

以下是這種情況：當我如下調用hql時，它告訴我它無法找到u1的別名。

hive> select user as u1, url as u2 from rank_test where u1 != ""; 
FAILED: SemanticException [Error 10004]: Line 1:50 Invalid table alias or column reference 'u1': (possible column names are: user, url) 

此問題與當我嘗試使用count(*) as cnt時相同。任何人都可以給我一些關於如何在where子句中使用別名的提示嗎？非常感謝！

hive> select user, count(*) as cnt from rank_test where cnt >= 2 group by user; 
FAILED: ParseException line 1:58 missing EOF at 'where' near 'user' 

Answer 1

的where子句的select子句前進行評估，這就是爲什麼你不能引用您的where子句中選擇別名。

但是，您可以引用派生表中的別名。

select * from (
    select user as u1, url as u2 from rank_test 
) t1 where u1 <> ""; 

select * from (
    select user, count(*) as cnt from rank_test group by user 
) t1 where cnt >= 2; 

邊注：寫最後的查詢更有效的辦法是

select user, count(*) as cnt from rank_test group by user 
having count(*) >= 2 

如果我沒記錯的話，你可以參照別名having即having cnt >= 2

Answer 2

我能在我的Hive select語句中使用反斜槓符號``使用別名。

SELECT COL_01 AS `Column_A`; 

上述解決方案適用於Hive版本1.2.1。

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