Question

我有以下sql查询：

page.c.Text="I found you";

表格的格式如下：

SELECT
     to_char(p.log_date, 'Mon') as mon,
     extract(year from p.log_date) as year,
from
     T
group by
     mon
having
     mon = 'september'
and
     year = '2018';

T没有列date col1 col2 2018/09/10 -- -- 2018/09/11 -- -- 2018/09/12 -- --和mon。我收到错误year的解决方法？

Answer 1

使用where子句不需要

SELECT
     to_char(p.log_date, 'Mon') as mon,
     extract(year from p.log_date) as year from your_table
where  to_char(p.log_date, 'Mon') = 'september'
and
     extract(year from p.log_date) = '2018'

由于没有聚合函数，因此这里group by不需要

而mon是您的列alis名称，在过滤器中找不到db引擎，因此抛出了错误。

注意：并非所有的dbms在过滤器中（位置或具有）都支持别名（别名）

Answer 2

尝试以下操作-在使用别名时发生

SELECT
     to_char(p.log_date, 'Mon') as mon,
     extract(year from p.log_date) as year
where to_char(p.log_date, 'Mon')= 'september'
and year = '2018';

Answer 3

在HAVING子句中使用别名会导致此问题。您可以在to_char（或HAVING子句）中使用WHERE表达式。但是为了避免代码复制，您应该执行子查询或CTE：

SELECT
     mon,
     year,
     ...
FROM (
    SELECT 
        to_char(p.log_date, 'Mon') as mon, 
        extract(year from p.log_date) as year,
        ... 
    FROM ...
)s
group by
     mon
having
     mon = 'september'
and
     year = '2018';

CTE：

WITH my_sub_query AS (
    SELECT 
        to_char(p.log_date, 'Mon') as mon, 
        extract(year from p.log_date) as year,
        ... 
    FROM ...
)
SELECT
     mon,
     year,
     ...
FROM my_sub_query
group by
     mon
having
     mon = 'september'
and
     year = '2018';

此外：

尝试使用WHERE代替HAVING
要按月和年分组，可以执行date_trunc('month', p.log_date)而不是to_char和extract

Answer 4

Having用于聚合函数条件，但是您不需要使用它，因为to_char和extract是正常函数。

我认为您忘记了使用FROM子句来选择表格。

SELECT
     to_char(p.log_date, 'Mon') as mon,
     extract(year from p.log_date) as year,
FROM T
WHERE 
    to_char(p.log_date, 'Mon') = 'september'
AND
    extract(year from p.log_date) = '2018';

Answer 5

这很简单，请尝试一下。

Select mon, [year] from (
  SELECT
     to_char(p.log_date, 'Mon') as mon,
     extract(year from p.log_date) as year,
 from T

) as DerivedTable

 where  mon = 'september' and  year = '2018'

group by mon

在“ group by”子句之后“具有”时出错

5 个答案: