计算具有空值和非空值的列数

Question

您好，我有一个查询，我想在单行中对 null(0,'', NULL) 和非 null 值求和。

示例：我有一个有 5 列的表格。它包含至少一条记录。在其第一行中，2 列是空白的，3 列具有一定的价值。我想要一个查询，它会给我一个类似 non_null_count=3, null_count=2

的结果

Answer 1

NOT NULL 数据计数-

SELECT Count(*) 
FROM   employee 
WHERE  salary IS NOT NULL 
       AND emp_name IS NOT NULL 
       AND manager_id IS NOT NULL 

NULL 数据计数-

SELECT Count(*) 
FROM   employee 
WHERE  salary IS NULL 
       AND emp_name IS NULL 
       AND manager_id IS NULL 

Answer 2

你可以用这个。

SELECT ( IF(col1 IS NOT NULL, 1, 0) 
         + IF(col2 IS NOT NULL, 1, 0) 
         + IF(col3 IS NOT NULL, 1, 0) +... ) AS total_not_null, 
       ( IF(col1 IS NULL, 1, 0) 
         + IF(col2 IS NULL, 1, 0) 
         + IF(col3 IS NULL, 1, 0) +... )     AS total_null 
FROM   mytable 

Answer 3

在 MySQL 中，布尔表达式可以被视为数字，“1”代表真，“0”代表假。

所以，这就是你想要的：

select ((col1 is not null) + (col2 is not null) + (col3 is not null) +
        (col4 is not null) + (col5 is not null)
       ) as num_not_null,
       ((col1 is null) + (col2 is null) + (col3 is null) +
        (col4 is null) + (col5 is null)
       ) as num_null
from t;

请注意，这会将“空白”解释为 NULL。如果“空白”有其他含义，您可以轻松使用<> '' 或类似逻辑。

编辑：

对于其他值，您需要扩展逻辑。一个简单的方法是：

select ((col1 is not null and col1 not in ('0', '')) +
        (col2 is not null and col2 not in ('0', '')) +
        (col3 is not null and col3 not in ('0', '')) +
        (col4 is not null and col4 not in ('0', '')) +
        (col5 is not null and col5 not in ('0', '')) 
       ) as num_not_null,
       ((col1 is null or col1 in ('0', '')) + 
        (col2 is null or col2 in ('0', '')) + 
        (col3 is null or col3 in ('0', '')) + 
        (col4 is null or col4 in ('0', '')) + 
        (col5 is null or col5 in ('0', '')) 
       ) as num_null
from t;