與同一列兩項

Question

我有兩個選擇查詢的選擇：

SELECT MONTH(date) AS month, count(DISTINCT ip) 
FROM table_name WHERE field = 1 GROUP BY month 

和

SELECT MONTH(date) AS month, count(DISTINCT ip) 
FROM table_name WHERE field = 2 GROUP BY month 

我怎麼能寫一個查詢來選擇

SELECT MONTH(date) AS month, 
     count(DISTINCT ip) [ for field = 1], 
     count(DISTINCT ip) [ for field = 2] 

Answer 1

SELECT MONTH(date) AS month, 
     count(DISTINCT case when field = 1 then ip end) as f1, 
     count(DISTINCT case when field = 2 then ip end) as f2 
FROM table_name 
WHERE field in (1,2) 
GROUP BY month