Question

我想将别名（其中有空格）与WHERE子句中的空格进行比较。

select r.resortid, sum(b.adultcount+b.childcount) as "Total Guest"
from   resort r, booking b
where  r.resortid = b.resortid and "Total Guest" <= 10
group by r.resortid
order by r.resortid;

我得到的错误是：

where  r.resortid=b.resortid and "Total Guest" <=10
                                 *
ERROR at line 3:
ORA-00904: "Total Guest": invalid identifier

Answer 1

使用HAVING子句并使用显式标准JOIN语法，而不要使用逗号分隔：

SELECT r.resortid, SUM(b.adultcount+b.childcount)
FROM resort r INNER JOIN
     booking b
     ON r.resortid = b.resortid 
GROUP BY r.resortid
HAVING SUM(b.adultcount+b.childcount) <= 10;

Where子句仅过滤原始数据，不对数据进行汇总。

Answer 2

鉴于度假村可能没有预订，我建议您使用left join：

select r.resortid, coalesce(sum(b.adultcount + b.childcount), 0) as total_guests
from resort r join
     booking b 
     on r.resortid = b.resortid 
group by r.resortid
having coalesce(sum(b.adultcount + b.childcount), 0) <= 10
order by r.resortid;

如果所有度假村都已预订，则join不是必需的：

select b.resortid, sum(b.adultcount + b.childcount) as total_guests
from booking b 
group by b.resortid
having sum(b.adultcount + b.childcount) <= 10
order by r.resortid;

Answer 3

您不能在同一条sql语句中定义的条件中引用别名。

在Oracle / MariaDB / MySQL数据库中，您有3种可能性：

1）重写计算列，如果它是由聚合函数计算的，则必须将条件放在“ HAVING”子句中：

SELECT r.resortid, sum(b.adultcount+b.childcount) as "Total Guest"
  FROM resort r, booking b
 WHERE r.resortid = b.resortid
 GROUP BY r.resortid
  HAVING sum(b.adultcount+b.childcount) <= 10
ORDER BY r.resortid;

2）使用子查询：

SELECT *
  FROM
    (SELECT r.resortid, sum(b.adultcount+b.childcount) as TotalGuest
      FROM resort r, booking b
     WHERE r.resortid = b.resortid
     GROUP BY r.resortid) AS totalg
 WHERE TotalGuest <= 10
ORDER BY resortid;

3）使用“ WITH”子句编写子查询：

WITH totalg AS
(SELECT r.resortid, sum(b.adultcount+b.childcount) as TotalGuest
  FROM resort r, booking b
 WHERE r.resortid = b.resortid
GROUP BY r.resortid)
SELECT *
  FROM totalg
 WHERE TotalGuest <= 10
ORDER BY resortid;

Answer 4

Having，而不是where；而且，JOIN不会造成任何伤害。

select r.resortid, 
       sum(b.adultcount + b.childcount) as "Total Guest"
from resort r join booking b on r.resortid = b.resortid 
group by r.resortid
having sum(b.adultcount + b.childcount) <= 10
order by r.resortid;

如何在WHERE子句中引用列别名

4 个答案: