將3個查詢優化爲單個查詢的最佳方式

Question

假設我有以下查詢。

SELECT count(*) FROM info WHERE info = 'a' and uid = 1 
SELECT count(*) FROM info WHERE info = 'b' and uid = 1 
SELECT count(*) FROM info WHERE info = 'c' and uid = 1; 

而不是編寫3個查詢有什麼辦法讓我可以在一個查詢中獲得所有這些細節？

Answer 1

SELECT info, count(*) as info_cnt 
FROM T 
WHERE uid = 1 and info IN ('a', 'b','c') 
GROUP BY info 

Answer 2

SELECT info, 
     SUM(CASE WHEN info = 'a' THEN 1 ELSE 0 END) `a`, 
     SUM(CASE WHEN info = 'b' THEN 1 ELSE 0 END) `b`, 
     SUM(CASE WHEN info = 'c' THEN 1 ELSE 0 END) `c` 
FROM tableName 
WHERE uid = 1 AND info IN ('a','b','c') 
GROUP BY info 

這會給你造成排

uid a b c 
============== 
1 5 2 6 

Answer 3

集團通過？

SELECT count(*) AS count, info FROM info WHERE uid=1 GROUP BY info 

count | info 
5  a 
10  b 
11  c