How to do a join in Oracle tables? - sql

Question

I am trying to help a co-worker do an inner join on two oracle tables so he can build a particular graph on a report.
I have no Oracle experience, only SQL Server and have gotten to what seems like the appropriate statement, but does not work.
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"
It doesn't like my aliases for some reason. It doesn't like not having quotes for some reason.
Also when I use the fully scored names it still fails because:
ORA-00933 SQL command not properly ended

Answer 1

The order of the query should be
SELECT
FROM
INNER JOIN
WHERE
GROUP BY
as below
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

In a flood of attempts, here's yet another one.
table2 can be moved out of subquery; join it with table1 on category as well
note that all non-aggregates columns (from the SELECT) have to be contained in the GROUP BY clause. It seems that a.timestamp contains more info than just month and day - if that's so, it'll probably ruin the whole result set as data won't be grouped by monthday, but by the whole date - consider removing it from SELECT, if necessary
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

The correct (simplified) syntax of select is
SELECT <columns>
FROM table1 <alias>
JOIN table2 <alias> <join_condition>
WHERE <condition>
GROUP BY <group by columns>

Answer 4

You are doing it wrong. Use subquery:
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

In addition to the order of the components other answers have mentioned (where goes after join etc), you also need to remove all of the double-quote characters. In Oracle, these override the standard naming rules, so "a.category" is only valid if your table actually has a column named, literally, "a.category", e.g.
create table demo ("a.category" varchar2(10));
insert into demo ("a.category") values ('Weird');
select d."a.category" from demo d;
It's quite rare to need to do this.

Answer 6

The query should look something like this:
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;
I'm not 100% sure this is what you want. Your query has numerous issues and complexities:
You don't need a subquery in the FROM clause.
You can use to_char() instead of the more complex date string processing.
The group by did not contain all the relevant fields.
Don't use double quotes, unless really, really needed.