Teradata MAX 功能 [英] Teradata MAX function

问题描述

如果我们使用下面的函数会返回哪一行?

Which row will be return if we use following function?

 MAX (NAME)

我们在名称列中有以下两行

Where we have following two rows in name column

1 ABC
2 ABC

推荐答案

两者都不是.将返回一个不绑定到任一行的聚合，而是 Max(Name) 值，显然必须是 ABC 因为它是唯一可用的值:

Neither. An aggregate will be returned that is not tied to either row, but rather the Max(Name) value, which will obviously have to be ABC as it's the only value available:

CREATE VOLATILE TABLE test
(
    f1 INTEGER,
    f2 CHAR(3)
) PRIMARY INDEX (f1) ON COMMIT PRESERVE ROWS;
INSERT INTO test VALUES (1, 'ABC');
INSERT INTO test VALUES (2, 'ABC');

SELECT MAX(f2) FROM test;

DROP TABLE test;

只返回ABC

你可以这样想.如果我在白板上写下数字2，让你大声说出哪个最大，你会说2"；问你选择了哪个'两个'?"是很愚蠢的.

You can think of it this way. If I write the number 2 on a whiteboard and ask you to say out loud which one is the largest, you will say "2"; it would be silly to ask "Which 'two' did you pick though?".

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