SQL查找列中每种类型的总数

Question

I'm learning SQL and am stumped on what should be a simple query. I have a table with the following pattern:

Id |  Type  
------------
1  |  Red   
2  |  Blue  
3  |  Blue  
4  |  Red   
..

I would like to write a query to return a table that counts the total number of instances of each type and returns a table with the following pattern, for example, if 'Blue' occurs in 12 rows, and 'Red' occurs in 16 rows in the table above, the result would be:

Blue | Red 
-----------
 12  |  16 

Answer 1

You could do it this way:

SELECT Type, COUNT(*) FROM TABLE GROUP BY Type

If you'd like to see the Types in separate columns, you could do this:

SELECT SUM(CASE WHEN Type = 'Blue' THEN 1 ELSE 0 END) AS Blue, SUM(CASE WHEN Type = 'Red' THEN 1 ELSE 0 END) AS Red FROM TABLE

Answer 2

I suggest using count over partition by . Here's a code I wrote to help my company check for duplicate Technician EmployeeID's and Pincodes, including count and YES/NO columns to allow filtering in excel so they can see what corrections need to be made:

select 
    t.TechnicianId, t.TechnicianName, t.Pincode, t.EmployeeID
    , [Pincode Count] = count(t.Pincode) over (partition by t.Pincode)
    , [Duplicate Pincode?] = case count(t.Pincode) over (partition by t.Pincode) when 1 then 'NO' else 'YES' end
    , [EmployeeID Count] = count(t.EmployeeID) over (partition by t.EmployeeID)
    , [Duplicate EmployeeID?] = case count(t.EmployeeID) over (partition by t.EmployeeID) when 1 then 'NO' else 'YES' end
from Technicians t
group by t.TechnicianId, t.TechnicianName, t.Pincode, t.EmployeeID
order by 4