Question

I have a big problem with combining 3 SQL queries into one simple query that returns me all I want. Is tehere any way to join these simple sql queries into one?

query1:

SELECT COUNT(FieldID) AS "CountA"
FROM table WHERE Rezervovany = 0 AND Prodany = 0

query2:

SELECT COUNT(FieldID) AS "CountB"
FROM table WHERE Rezervovany = 1 AND Prodany = 0

query3:

SELECT COUNT(FieldID) AS "CountC"
FROM table WHERE Prodany = 1

Answer 1

You can put your conditions in a case clause inside the aggregate count function:

SELECT Count(CASE 
               WHEN rezervovany = 0 AND prodany = 0 THEN fieldid 
               ELSE NULL 
             END) AS "CountA", 
       Count(CASE 
               WHEN rezervovany = 1 AND prodany = 0 THEN fieldid 
               ELSE NULL 
             END) AS "CountB", 
       Count(CASE 
               WHEN prodany = 1 THEN fieldid 
               ELSE NULL 
             END) AS "CountC" 
FROM   table 

Keep in mind that count only counts non-null values.