计算 MySQL 列中子字符串的出现次数

2021-12-30 00:00:00 select count mysql

我有一个表，其中存储了许多推特推文的信息，包括推文文本和发布推文的用户的屏幕名称.推文包含主题标签(以 # 开头)，我想计算特定用户发推文的主题标签数量:

I have a table which stores information of a lot of twitter tweets including the tweet text and the screen name of the user who tweeted the tweet. The tweets contain hashtags (starting with #), I want to count the number of hashtags that a specific user has tweeted:

tweet_id |                       tweet_text                           | screen_name    |
--------------------------------------------------------------------------------------------
       1 | #hashtag1 #otherhashtag2 #hashtag3 some more text          | tweeter_user_1 |
       2 | some text #hashtag1 #hashtag4 more text                    | tweeter_user_2 |
       3 | #hashtag5 #hashtag1 @not a hashtag some#nothashtag         | tweeter_user_1 |
       4 | #hashtag1 with more text                                   | tweeter_user_3 |
       5 | #otherhashtag2 #hashtag3,#hashtag4 more text               | tweeter_user_1 |

如果我要计算 tweeter_user_1 的主题标签，我期望的结果是 8，如果我想要 tweeter_user_3 的主题标签，它应该返回 1.假设我的表名是推文，我该怎么做.

If I were to count the hashtags of tweeter_user_1, the result i expect is 8, if i wanted the hashtags of tweeter_user_3 it should return 1. How can I do it assuming that my table name is tweets.

我试过这个: SELECT COUNT( * ) FROM tweets WHERE( LENGTH( REPLACE( tweet_text, '#%', '@') = 0 ) ) AND screen_name = 'tweeter_user_1' 但它没用

I tried this: SELECT COUNT( * ) FROM tweets WHERE( LENGTH( REPLACE( tweet_text, '#%', '@') = 0 ) ) AND screen_name = 'tweeter_user_1' but it didn't work

如果 tweeter_user_1 的结果也是 9，我会很高兴 :D

I would be happy if the result of tweeter_user_1 was 9 too :D

推荐答案

这应该会给你一个 screen_names 列表和他们使用的所有主题标签的总数.

This should give you a list of screen_names and the total count of all hashtags they use.

SELECT  foo.screen_name, SUM(foo.counts) FROM 
  (
    SELECT screen_name, 
           LENGTH( tweet_text) - LENGTH(REPLACE(tweet_text, '#', '')) AS counts 
    FROM tweet_table 
  ) as foo 
GROUP BY  foo.screen_name

但是......如果表很大，这是一个令人讨厌的查询.如果您只需要对单个用户进行计数，我可能会在内部选择中指定特定用户.像这样:

But.... it's a nasty query if the table is huge. I might specify a specific users in the inner select if you just need counts for a single user. Like this:

SELECT  foo.screen_name, SUM(foo.counts) FROM 
 (
    SELECT screen_name, 
         LENGTH( tweet_text) - LENGTH(REPLACE(tweet_text, '#', '')) AS counts 
    FROM tweet_table WHERE  screen_name = 'tweeter_user_1' 
 ) as foo 
GROUP BY  foo.screen_name

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