mysql - 在表的所有行中查找具有空值的列

Question

我正在搜索一个 SQL 请求，该请求为我提供了一个表中从未填充过的所有列。

例如，在这样的表格中:

column 1 | column 2 | column 3 | column 4 | column 5
---------+----------+----------+----------+---------
value    | NULL     | value    | value    | NULL
NULL     | NULL     | value    | value    | NULL
value    | NULL     | value    | NULL     | NULL
value    | NULL     | value    | value    | NULL

The request will return :

column 2, column 5

EDIT :

I've created this little PHP script to generate the query and print the result :

$columns = $sql->select("SELECT column_name FROM information_schema.COLUMNS WHERE TABLE_NAME='table_name'");

$query = "SELECT ";
foreach($columns as $column) {
    $query .= "case when count(".$column[0].") = 0 then '".$column[0]."' end, ";
}
$query = substr($query, 0,-2);
$query .= " FROM table_name";

var_dump($sql->select($query));

Answer 1

类似于:

select case when count(column1) = 0 then 'column 1' end,
       case when count(column2) = 0 then 'column 2' end,
       case when count(column3) = 0 then 'column 3' end,
       case when count(column4) = 0 then 'column 4' end,
       case when count(column5) = 0 then 'column 5' end
from tablename

即计算一列的所有值，如果找到 0，则返回列名。