SQL选择不同的值，如其他值

Question

So I have a table that is automatically generated by an instant messenger application and I am looking for all messages sent by all users. Each conversation has a "to" column the problem is that it appends a short connection string on the end. so the to column looks like: username @company.com/id 1111

I am looking to get all distinct usernames and the number of times they appear. Any suggestions are appreciated. I am using PostgreSQL 9.1.1

Answer 1

The problem is parsing the string. This depends highly on the dialect of SQL. Here is an approach using MySQL:

select substring_index(`to`, '/', 1) as username, count(*)
from t
group by substring_index(`to`, '/', 1);

In most other SQL dialects, the logic would be slightly different. In SQL Server:

select left("to", charindex('/', "to") - 1) as username, count(*)
from t
group by left("to", charindex('/', "to") - 1);

In other databases, the equivalent of charindex() might be instr() or position() .

EDIT:

I originally miinterpreted the "username" as being the entire email address. Barmar has pointed out that the formatting in the question really suggests the part before the @ . Having just the user name portion of the email, without the domain, seems dangerous. But, the above works, just by substituting '@' for '/' :

select substring_index(`to`, '@', 1) as username, count(*)
from t
group by substring_index(`to`, '@', 1);

select left("to", charindex('@', "to") - 1) as username, count(*)
from t
group by left("to", charindex('@', "to") - 1);

Answer 2

Is there any commonality/shared characteristic of this 'connection string' ?

If so, then is just a question of creating the string manipulation to help you disregard it in your SQL query.

Without knowing the pattern of the connection string, would be hard to supply an answer.