需要使用subselect獲得一行結果

Question

有這樣的SQL查詢：

SELECT 
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 1") AS test_1 , 
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 2") AS test_2 , 
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 3") AS test_3 
FROM `table_name` GROUP BY `content`

並得到這樣的結果：

test_1, test_2, test_3
2,      7,      0
2,      7,      0
2,      7,      0
2,      7,      0
2,      7,      0
2,      7,      0
2,      7,      0
2,      7,      0
2,      7,      0
2,      7,      0

只需要一行就可以得到結果，像這樣：

test_1, test_2, test_3
2,      7,      0

怎么樣？ 我的查詢出了什么問題？

Answer 1

檢查一下。

SELECT  distinct 
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 1") AS test_1 , 
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 2") AS test_2 , 
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 3") AS test_3 
FROM `table_name` GROUP BY `content`

Answer 2

您的查詢應該這樣重寫：

SELECT 
    SUM(CASE WHEN `content` = "test 1" THEN 1 ELSE 0 END) AS test_1,
    SUM(CASE WHEN `content` = "test 2" THEN 1 ELSE 0 END) AS test_2,
    SUM(CASE WHEN `content` = "test 3" THEN 1 ELSE 0 END) AS test_3
FROM 
    `table_name`
WHERE 
    `custom_id` IN (10,9,8,6,5,4,3,2,1);

Answer 3

只需在您的SELECT語句中添加TOP子句即可。

SELECT TOP 1
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 1") AS test_1 , 
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 2") AS test_2 , 
(SELECT COUNT(`id`) FROM `table_name` WHERE `custom_id` IN (10,9,8,6,5,4,3,2,1) AND `content` = "test 3") AS test_3 
FROM `table_name` GROUP BY `content`

Answer 4

你在做什么沒有多大意義。 您從表中選擇並按內容分組。 這意味着您為每個內容獲得一個結果行（一個用於“ test 1”，一個用於“ test 2”，等等）。 表中顯示了十個不同的內容，因為您顯示將獲得十個結果行。

然后，對於每一個這樣的行，無論它包含什么內容，您都在執行三個子查詢，這些子查詢當然總是得到相同的結果。

所以：

select 
  (select count(*) from table_name 
    where custom_id in (10,9,8,6,5,4,3,2,1) and content = 'test 1') as test_1 , 
  (select count(*) from table_name 
    where custom_id in (10,9,8,6,5,4,3,2,1) and content = 'test 2') as test_2 , 
  (select count(*) from table_name
    where custom_id in (10,9,8,6,5,4,3,2,1) and content = 'test 3') as test_3 ;

或更好：

select 
  sum(content = 'test 1') as test_1,
  sum(content = 'test 2') as test_2,
  sum(content = 'test 3') as test_3
from table_name
where custom_id in (10,9,8,6,5,4,3,2,1);