MySQL:仅获取非空列

Question

有表:

我需要获取具有“列”指定值的非空列。

试试这个

select * from table where category='1-137-2891' and defence is not null and type is not null

但显然得到的是空集。

Answer 1

我想我已经为您找到了答案。

假设你有这样的表:

create table t (a int, b int);
insert into t (a, b) values (1, null);

然后，您可以创建动态SQL语句并使用EXECUTE命令执行；

set @sql = (select concat('select ',
case when sum(a) is null then '' else 'A' end,
case when sum(b) is null then '' else ', ' end, 
case when sum(b) is null then '' else 'B' end,
              ' from t')
from t);

prepare stmt FROM @sql;
execute stmt;
deallocate prepare stmt;

Here is an example