如何在 Oracle 表中进行联接？

Question

我正在尝试帮助一位同事对两个 oracle 表进行内部联接，以便他可以在报表上构建特定图表。

我没有 Oracle 经验，只有 SQL Server，并且得到了看起来合适的语句，但不起作用。

SELECT concat(concat(month("a.timestamp"),','),day("a.timestamp")) as monthDay
    , min("a.data_value") as minTemp
    , max("a.data_value") as maxTemp
    , "b.forecast" as forecastTemp
    , "a.timestamp" as date
FROM table1 a
WHERE "a.category" = 'temperature'
GROUP BY concat(concat(month("timestamp"),','),day("timestamp"))
INNER JOIN (SELECT "forecast"
           , "timestamp"
        FROM table2
        WHERE "category" = 'temperature') b
ON "a.timestamp" = "b.timestamp"

出于某种原因，它不喜欢我的别名。它不喜欢由于某种原因没有引号。

此外，当我使用完整评分的名称时，它仍然失败，因为：

ORA-00933 SQL command not properly ended

Answer 1

查询的顺序应该是

SELECT
FROM
INNER JOIN
WHERE
GROUP BY

如下

SELECT concat(concat(month("a.timestamp"),','),day("a.timestamp")) as monthDay
    , min("a.data_value") as minTemp
    , max("a.data_value") as maxTemp
    , "b.forecast" as forecastTemp
    , "a.timestamp" as date
FROM table1 a
INNER JOIN (SELECT "forecast"
       , "timestamp"
      FROM table2
      WHERE "category" = 'temperature') b
ON "a.timestamp" = "b.timestamp"
WHERE "category" = 'temperature'
GROUP BY concat(concat(month("timestamp"),','),day("timestamp"))

Answer 2

在大量尝试中，这里还有一个。

• table2 可以移出子查询；也将它与 table1 的类别一起加入
• 请注意，所有非聚合列（来自 SELECT）都必须包含在 GROUP BY 子句中。似乎a.timestamp 包含的信息不仅仅是 月和日 - 如果是这样，它可能会破坏整个结果集，因为数据不会按 月日分组>，但在整个日期之前 - 如有必要，请考虑将其从 SELECT 中删除

---

SELECT TO_CHAR(a.timestamp,'mm.dd') monthday,
      MIN(a.data_value) mintemp,
      MAX(a.data_value) maxtemp,
      b.forecast forecasttemp,
      a.timestamp c_date
FROM table1 a
JOIN table2 b ON a.timestamp = b.timestamp
             AND a.category = b.category
WHERE a.category = 'temperature'
GROUP BY TO_CHAR(a.timestamp,'mm.dd'),
         b.forecast,
         a.timestamp;

Answer 3

select 的正确（简化）语法是

SELECT <columns>
FROM table1 <alias>
   JOIN table2 <alias> <join_condition>
WHERE <condition>
GROUP BY <group by columns>

Answer 4

你做错了。使用子查询：

SELECT c.*,  b.`forecast` as forecastTemp
FROM
(SELECT concat(concat(month(a.`timestamp`),','),day(a.`timestamp`)) as monthDay
    , min(a.`data_value`) as minTemp
    , max(a.`data_value`) as maxTemp
    , a.`timestamp` as date
FROM table1 a
WHERE `category`='temperature'
GROUP BY concat(concat(month(`timestamp`),','),day(`timestamp`))) c
INNER JOIN (SELECT `forecast`
           , `timestamp`
        FROM table2
        WHERE `category` = 'temperature') b
ON c.`timestamp` = b.`timestamp`;

Answer 5

除了其他答案提到的组件顺序（where 在join 等之后），您还需要删除所有双引号字符。在 Oracle 中，这些会覆盖标准命名规则，因此 "a.category" 仅在您的表实际上有一个名为 "a.category" 的列时才有效，例如

create table demo ("a.category" varchar2(10));

insert into demo ("a.category") values ('Weird');

select d."a.category" from demo d;

很少需要这样做。

Answer 6

查询应该如下所示：

SELECT to_char(a.timestamp, 'MM-DD') as monthDay,
       min(a.data_value) as minTemp,
       max(a.data_value) as maxTemp,
       b.forecast as forecastTemp
FROM table1 a JOIN
     table2 b
     ON a.timestamp = b.timestamp and b.category = 'temperature'
WHERE a.category = 'temperature'
GROUP BY to_char(timestamp, 'MM-DD'), b.forecast;

我不是 100% 确定这是您想要的。您的查询有很多问题和复杂性：

• FROM 子句中不需要子查询。
• 您可以使用to_char() 代替更复杂的日期字符串处理。
• group by 未包含所有相关字段。
• 不要使用双引号，除非真的非常需要。