sql - 如何删除数据库中的最后一行（全为 NULL）？

Question

Column1  Column2  Column3  Column4  Column5  Column6
NULL    NULL     NULL   NULL     NULL     NULL

我尝试了以下查询：

1.

Delete from tablename where column1 = NULL

2.

Delete from tablename where column1 IS NULL

第二个查询成功完成，但它说 0 行受到影响。

Answer 1

is null尝试匹配空值时必须使用特殊语法：

delete from mytable
where Column1 is null
and Column2 is null
and Column3 is null
and Column4 is null
and Column5 is null
and Column6 is null;

任何常规比较null总是错误的，

例如两者Column1 = null和Column1 != null总是false

Answer 2

我相信这对您的 rdbms 或等效项应该有效。如果 isnull 函数的返回值等于空字符串，它将删除行。

DELETE FROM tablename
WHERE isnull(Column1, '') = ''

Answer 3

DELETE FROM table WHERE coalesce(col1,col2,col3,...) IS NULL