Question

I have three columns in a table:

score  status  No.
1,     2,      1
0,     1,      2
0,     0,      1

I need this, to write a C# style pseudo SQL:

rows = empty;

rows = "SELECT * FROM `table` WHERE score = 1"
if (rows.Count > 0) //at least one row
    return rows;

rows = "SELECT * FROM `table` WHERE status = 2"
if (rows.Count > 1) //more than one row 
    return row with MAX(No.) from rows; //ie MAX(No.) where status = 2

 return rows;

I hope I could be clear. In short, select from my table records with score = 1, and if there isn’t such a record, return the record where status = 2 and if there are more than one record with status = 2, then return the record with maximum value for No. where status = 2 (if no record at all with status = 2, return empty).

How can I write it in one query? It should be a good learning experience for me. Otherwise I know to breakup into smaller queries and run each one. And I can’t go with stored procedures right now..

Edit: Actually my query will have a few more WHERE clauses but identical in both the conditions and that is why I omitted it. Hence, regarding the first condition, there will be only one record returned for now. That is SELECT * FROM table WHERE score = 1 will return just one row for now. And I need / I’ll accept answers that gives such a solution too. But the point is you never know, may be in future with some design changes, there could be more rows with score = 1. That is why I went for records instead of record. But ideally the business logic is to have all records with score = 1. For now, record will do. I’m just thinking query will be much simpler if only one row is returned and my teammates can assimilate the code easily.

Final Update: Thank you all guys, you’ve been very kind 🙂 Many answers worked well, and choosing one is really really daunting. My finding on the answers:

1. Answers which worked always: @GordonLinoff’s, @ZaneBiens’s, @ZaneBien’s another, @Scen’s, @JulienCh.’s (the last 3 being essentially the same, but yet I am not fully aware how those worked :))

2. Answers which worked only when first condition score = 1 returned only one row: @HannoBinder’s, @ShlomiNoach’s, @DaniellePaquette-Harvey’s. For the moment, I ‘ll stick with @Danielle’s (which is freakingly simple) and later revert if there arises need to have more than one row)

3. Rest of the answers, I couldn’t test as they were either not very specific or not related to MySQL.

4. @MatthewPK’s is not appropriate in the context.

Awarding the bounty and accepting an answer is tough with so many right answers. I chose this one since I felt it is probably more efficient and readable too, but I’ll accept @Scen’s answer for being downright simple.

Answer 1

Select *
From scores
Where score = 1
UNION
(
   Select *
   From scores
   Where status = 2 and not exists (Select * from scores where score = 1)
   Order By `No.` desc
   Limit 1
);

I named table as scores.

SqlFiddle (Query with some fake schema so you can see the results):
http://sqlfiddle.com/#!2/6aac2/1/0

EDIT: edited SQlFiddle to match the fake schema with the one in the question.