Question

我有一张看起来像这样的表

id          +        kID       
--------------------------
0           |         3
1           |         6
2           |         7
3           |         6
4           |         7
5           |         5

我想要做的是找到kID仅出现一次的行数。所以在这种情况下，变量的值应该是2，因为kID: 3 and 5 occurs only once所以我试图计算它而忽略其他所有内容。我真的很难过，谢谢你的帮助。

Answer 1

这将显示仅出现一次的kID：

SELECT kID, COUNT(kID)
FROM table
GROUP BY kID
HAVING COUNT(kID) < 2

<强>结果

| KID | COUNT(KID) |
--------------------
|   3 |          1 |
|   5 |          1 |

See the demo

然后得到那些的总数：

SELECT Count(*) AS count 
FROM   (SELECT kid, 
               Count(kid) 
        FROM   tbl 
        GROUP  BY kid 
        HAVING Count(kid) < 2) a

<强>结果

| COUNT |
---------
|     2 |

See the demo

Answer 2

试试这个

SELECT
  id,
  count(kID) as `Count`
FROM mytable as t
GROUP BY kID
HAVING Count = 1

Answer 3

怎么样

select count(*) from 
(select kid, count(*) from table group by kid having count(*) = 1)

Answer 4

您可以执行以下操作：

select count(*) from 
(
    select kID, COUNT(*) [c] from tableName
    group by kID
) t
where t.c = 1

Answer 5

SELECT kID, 
COUNT(kID) 
FROM tableName
GROUP BY kID
HAVING COUNT(kID) = 1

Answer 6

您可以通过子选择来完成。这应该有效，但可能效率不高：

SELECT id, kID, COUNT(1) FROM (SELECT COUNT(1),kID FROM TABLE
                               GROUP BY kID
                               HAVING COUNT = 1)

Answer 7

另一种方法。只要(id)是表的主键或(kid, id)上有唯一约束，它就会起作用：

SELECT COUNT(*) AS cnt
FROM
  ( SELECT NULL
    FROM tableX
    GROUP BY kid
    HAVING MIN(id) = MAX(id) 
  ) AS g ;

在 SQL-Fiddle

进行测试

(kid, id)上的索引可以提高效率 - 只会完成一个COUNT()，而不是2. {/ p>

PHP MySQL如何获取列完全唯一的行数

7 个答案: