具有空值时的SQL排序

我必须按数值升序排列sql结果。 我的代码是这样的：

ORDER BY CAST(`baseData` AS DECIMAL(10,2)) {$dir} ";

它工作得很好，但有一个问题：它将所有空值放在底部，我认为它将它们视为“0”。 我需要在底部放置所有空值，如何修改它？

试试这个SQL

对于MYSQL

ORDER BY COALESCE(CAST(`baseData` AS DECIMAL(10,2)),0)

甲骨文

ORDER BY NVL(CAST(baseData AS DECIMAL(10,2)),0)

MySQL 5.5.30架构设置：

create table test(
t varchar(5)
);


insert into  test
values('123'),('234'),('222'),(NULL);

select coalesce(cast(t as decimal(10,2)),0)
from test
order by coalesce(cast(t as decimal(10,2)),0);

| COALESCE(CAST(T AS DECIMAL(10,2)),0) |
----------------------------------------
|                                    0 |
|                                  123 |
|                                  222 |
|                                  234 |

查询1：

create table test(
t varchar(5)
);


insert into  test
values('123'),('234'),('222'),(NULL);

select coalesce(cast(t as decimal(10,2)),0)
from test
order by coalesce(cast(t as decimal(10,2)),0);

| COALESCE(CAST(T AS DECIMAL(10,2)),0) |
----------------------------------------
|                                    0 |
|                                  123 |
|                                  222 |
|                                  234 |

：

create table test(
t varchar(5)
);


insert into  test
values('123'),('234'),('222'),(NULL);

select coalesce(cast(t as decimal(10,2)),0)
from test
order by coalesce(cast(t as decimal(10,2)),0);

| COALESCE(CAST(T AS DECIMAL(10,2)),0) |
----------------------------------------
|                                    0 |
|                                  123 |
|                                  222 |
|                                  234 |

---

如果你想把所有的空都放在头上

  ORDER BY CAST(`baseData` AS DECIMAL(10,2)) NULLS FIRST 

如果要将所有空值都放在底部

  ORDER BY CAST(`baseData` AS DECIMAL(10,2)) NULLS LAST

如果希望将空值视为0，请像Pheonix那样强制转换它们

  ORDER BY Nvl(CAST(`baseData` AS DECIMAL(10,2)), 0) -- Oracle, MS SQL
  ORDER BY IfNull(CAST(`baseData` AS DECIMAL(10,2)), 0) -- MySQL

如果希望空值是最后一个，但显示为0

  select ...
         Nvl(CAST(`baseData` AS DECIMAL(10,2)), 0) -- Oracle, MS SQL
         ...
   order by CAST(`baseData` AS DECIMAL(10,2)) NULLS LAST

是的，它起作用了：

ORDER BY baseData = '', CAST(`baseData` AS DECIMAL(10,2)) {$dir} ";

---

不，它会随机化结果（我使用的是MySql）更新后的答案在您的示例中没有order by子句。但是我应该把参数“asc”或“desc”放在哪里呢？最后一个空值之后或之前？按[Your Expression]排序ASC最后一个空值