问题
What is wrong with my sql statement, it says that the problem is near the FULL JOIN, but I'm stumped:
SELECT `o`.`name` AS `offername`, `m`.`name` AS `merchantName`
FROM `offer` AS `o`
FULL JOIN `offerorder` AS `of` ON of.offerId = o.id
INNER JOIN `merchant` AS `m` ON o.merchantId = m.id
GROUP BY `of`.`merchantId`
Please be gentle, as I am not a sql fundi
回答1:
MySQL doesn't offer full join, you can either use
- a pair of LEFT+RIGHT and UNION; or
- use a triplet of LEFT, RIGHT and INNER and UNION ALL
The query is also very wrong, because you have a GROUP BY but your SELECT columns are not aggregates.
After you convert this properly to LEFT + RIGHT + UNION, you still have the issue of getting an offername and merchantname from any random record per each distinct of.merchantid, and not even necessarily from the same record.
Because you have an INNER JOIN condition against o.merchant, the FULL JOIN is not necessary since "offerorder" records with no match in "offer" will fail the INNER JOIN. That turns it into a LEFT JOIN (optional). Because you are grouping on of.merchantid, any missing offerorder records will be grouped together under "NULL" as merchantid.
This is a query that will work, for each merchantid, it will show just one offer that the merchant made (the one with the first name when sorted in lexicographical order).
SELECT MIN(o.name) AS offername, m.name AS merchantName
FROM offer AS o
LEFT JOIN offerorder AS `of` ON `of`.offerId = o.id
INNER JOIN merchant AS m ON o.merchantId = m.id
GROUP BY `of`.merchantId, m.name
Note: The join o.merchantid = m.id is highly suspect. Did you mean of.merchantid = m.id? If that is the case, change the LEFT to RIGHT join.
来源：https://stackoverflow.com/questions/4798698/mysql-statement-syntax-error-on-full-join