如何获取一列中值的数量计数？

Question

I have a table called tbl_company . It has the fields

id  comp_name     followers
 1    abc         15,23,88,99
 2    bbc         1,10,66

In followers field i am saving the employees id of those who are following that company. This works fine. In code behind, each company page, I want to display how many followers have them

example in abc company page i want show

No of people following is 4

example in bbc company page i want show

No of people following is 3

like this i want to display.how i can get this count.....

Thanks

Answer 1

Comma-separated lists in a database field are unwieldy and in general a really bad idea. The main reason being it completely nullifies the reason to use a relational database in the first place (eg indexes, foreign keys, and joins).

You should normalize your database so you instead have:

tbl_company
--------------
id   comp_name
1    abc
2    bbc

company_followers
----------------------
company_id follower_id
1          15
1          23
1          88
1          99
2           1
2          10
2          66

Then you can simply execute the following SQL:

SELECT COUNT(1)
FROM company_followers
WHERE company_id = @company_id

---

If you're absolutely stuck with this schema, you should first complain to whoever wrote it if possible <g>, then the simplest solution is to return the whole darn string and count the commas in C# (and add 1 of course).

Answer 2

Here's TSQL version,

SELECT  ID, 
        Comp_name, 
        CASE WHEN LEN(followers) > 0
             THEN (LEN(followers) - LEN(REPLACE(followers, ',', '')) + 1)
             ELSE 0
        END as FollowerCount 
FROM    tableName

• SQLFiddle Demo

In MySQL

SELECT  ID, 
        Comp_name, 
        CASE WHEN CHAR_LENGTH(followers) > 0
             THEN (CHAR_LENGTH(followers) - CHAR_LENGTH(REPLACE(followers, ',', '')) + 1)
             ELSE 0
        END as FollowerCount 
FROM    tableName

• SQLFiddle Demo

Answer 3

This is not a good database design. You must think twice using this sort of table structure. This can be further normalized. If you don't properly do this at the beginning it could cause problems later and is not expandable. So, it would be better if you could change the table structure.

The data will look like the following with new table structure.

company table:

id     comp_name
1      abc
2      bbc

company_follower table:

company_id     follower
1              15
1              23
1              88
1              99
2              1
2              10
2              66

Then your query for your result is,

SELECT COUNT(company_id)
  FROM company_follower
  WHERE company_id = @company_id;