为什么MySQL在FULL OUTER JOIN上报告语法错误？

SELECT airline, airports.icao_code, continent, country, province, city, website FROM airlines FULL OUTER JOIN airports ON airlines.iaco_code = airports.iaco_code FULL OUTER JOIN cities ON airports.city_id = cities.city_id FULL OUTER JOIN provinces ON cities.province_id = provinces.province_id FULL OUTER JOIN countries ON cities.country_id = countries.country_id FULL OUTER JOIN continents ON countries.continent_id = continents.continent_id 

它说

你的SQL语法有错误; 检查对应于您的MySQL服务器版本的手册，以便在第4行的“airlines.iaco_code = airports.iaco_code full outer join”的“外部joinairports ”附近使用正确的语法

语法看起来很正确。 我以前从来没有做过很多的连接，但是我需要一个由各种id交叉引用的表中的列。

Answer 1

MySQL中没有FULL OUTER JOIN 。 见7.2.12。 外部简化和12.2.8.1。 JOIN语法 ：

您可以使用UNION（从MySQL 4.0.0开始）模拟FULL OUTER JOIN ：

用两张表t1，t2：

 SELECT * FROM t1 LEFT JOIN t2 ON t1.id = t2.id UNION SELECT * FROM t1 RIGHT JOIN t2 ON t1.id = t2.id 

有三个表格t1，t2，t3：

 SELECT * FROM t1 LEFT JOIN t2 ON t1.id = t2.id LEFT JOIN t3 ON t2.id = t3.id UNION SELECT * FROM t1 RIGHT JOIN t2 ON t1.id = t2.id LEFT JOIN t3 ON t2.id = t3.id UNION SELECT * FROM t1 RIGHT JOIN t2 ON t1.id = t2.id RIGHT JOIN t3 ON t2.id = t3.id 

Answer 2

克莱图斯的答案并不完全正确。 UNION将删除FULL OUTER JOIN将包含的重复logging。 如果你需要使用类似的东西重复：

 SELECT * FROM t1 LEFT JOIN t2 ON t1.id = t2.id LEFT JOIN t3 ON t2.id = t3.id LEFT JOIN t4 ON t3.id = t4.id UNION ALL SELECT * FROM t1 RIGHT JOIN t2 ON t1.id = t2.id LEFT JOIN t3 ON t2.id = t3.id LEFT JOIN t4 ON t3.id = t4.id WHERE t1.id IS NULL UNION ALL SELECT * FROM t1 RIGHT JOIN t2 ON t1.id = t2.id RIGHT JOIN t3 ON t2.id = t3.id LEFT JOIN t4 ON t3.id = t4.id WHERE t2.id IS NULL UNION ALL SELECT * FROM t1 RIGHT JOIN t2 ON t1.id = t2.id RIGHT JOIN t3 ON t2.id = t3.id RIGHT JOIN t4 ON t3.id = t4.id WHERE t3.id IS NULL; 

Answer 3

我刚刚为此做了一个诡计：

 (select 1 from DUAL) d LEFT OUTER JOIN t1 ON t1.id = t2.id LEFT OUTER JOIN t2 ON t1.id = t2.id 

问题是，来自dual的查询会产生一个固定点，并且mysql可以外部连接另外两个表