mysql - 给出 MySQL 表中 Null 值的位置

Question

我有一个混合了空值和非空值的表，我想在迁移到其他源之前比较空值在表中的位置

mysql> select * from student2;
+------+---------+------------+
| id   | name    | address    |
+------+---------+------------+
|   10 | Rams    | NULL       |
|   12 | Hari    | NULL       |
|   13 | Shyam   | NULL       |
|   14 | NULL    | Hyderabad  |
|      | Revathy | Singapore  |

我期望输出只有 Null 值的位置以及行号，即

Row Number 1 Column Number 3
Row Number 2 Column Number 3
Row Number 3 Column Number 3
Row Number 4 Column Number 1
Row Number 5 Column Number 1

Answer 1

我认为这个查询可以帮助您:

SELECT (SELECT COUNT(*)
        FROM student2 si
        WHERE si.id <= s.id) As RowNo,
       CASE WHEN s.name IS NULL THEN 1
            WHEN s.address IS NULL THEN 2
       END As ColumnNo
FROM student2 s
WHERE COALESCE(s.name, s.address, '0') <> '0'