Count occurrences of a sub string in a MySQL column

Question

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 |

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.

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

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

Answer 1

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

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

Answer 2

Depending on how often you need to run the query, you could be causing MySQL to spend a lot of CPU time parsing and reparsing the tweet_text column. I would strongly recommend adding a hashtag_qty column (or similar) and store the count of hashtag elements there when you populate the row to begin with.