sql - 多列输出中的不同列值（然后转换为 CSV）

Question

我有以下查询：

SELECT first, last, title, email, org 
FROM people WHERE email <> "" 
INTO OUTFILE 'C:/testfile.csv' FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\n'

哪个有效。我需要选择不同的电子邮件（我不希望同一电子邮件中有多个条目）。

它会像这样工作吗？：

SELECT first, last, title, distinct(email), org 
FROM people WHERE email <> "" 
INTO OUTFILE 'C:/testfile.csv' FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\n'

Answer 1

您使用的是哪个平台/版本的 SQL？通常，这将通过 group by 语句来完成。就像是：

SELECT first, last, title, email, org 
FROM people 
GROUP BY Email
WHERE email <> ""
INTO OUTFILE 'C:/testfile.csv' FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\n'

以上内容实际上适用于某些平台/版本的 SQL，但“正确”（标准 sql）方法如下（当然，如果同一电子邮件的其他字段不同，您会得到未定义的结果）：

SELECT max(first), max(last), max(title), email, max(org) 
FROM people 
GROUP BY Email
WHERE email <> ""
INTO OUTFILE 'C:/testfile.csv' FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\n'