Question

我按以下方式进行查询：

SELECT * FROM frequency WHERE docid = '10398_txt_earn' AND count = 1
UNION
SELECT * FROM frequency WHERE docid = '925_txt_trade' AND count = 1;

输出正确

docid   term    count
10398_txt_earn  100     1
10398_txt_earn  11340   1
10398_txt_earn  12  1
10398_txt_earn  1204    1
10398_txt_earn  198485  1
10398_txt_earn  20  1
10398_txt_earn  27  1
10398_txt_earn  28  1

现在我想用COUNT（）运算符计算结果中的行数，但我不知道应用它。提前致谢

Ubuntu14.04 SQLite with XAMPP

Answer 1

你在找这个吗？

select count(*)
FROM (SELECT * FROM frequency WHERE docid = '10398_txt_earn' AND count = 1
      UNION
      SELECT * FROM frequency WHERE docid = '925_txt_trade' AND count = 1
     ) t;

顺便说一句，您可以更有效地编写原始查询：

SELECT *
FROM frequency
WHERE count = 1 and (docid in  '10398_txt_earn', '925_txt_trade');

然后计数：

SELECT count(*)
FROM frequency
WHERE count = 1 and (docid in  '10398_txt_earn', '925_txt_trade');

Answer 2

你可以这样做：

SELECT COUNT(1)
FROM 
(
  SELECT * FROM frequency WHERE docid = '10398_txt_earn' AND count = 1
  UNION
  SELECT * FROM frequency WHERE docid = '925_txt_trade' AND count = 1
) a

由于您使用了＆＃39; UNION＆＃39;，您的结果将删除重复项。如果您想要包含所有记录（包括任何重复记录），请使用UNION ALL代替UNION。

使用count（）运算符和SQL查询

2 个答案: