mysql - 在多个表sql中的同一列上选择不同的

Question

这里是 SQL 新手。

我有这个架构:

我需要简单的英语是:

“在 2 列中，将一列放在另一列上方，然后计算有多少个不同值”

我已经尝试过

SELECT COUNT (DISTINCT uid ) from nodes  UNION SELECT COUNT (DISTINCT uid) from ways ;

SELECT   distinct nodes.uid  from nodes  JOIN ways on nodes.uid = ways.uid ;

sqlite> SELECT COUNT (DISTINCT uid ) from nodes  UNION SELECT COUNT (DISTINCT uid) from ways ;
1195
2182
sqlite> SELECT   uid  from nodes  FULL OUTER JOIN ways on nodes.uid = ways.iud ;
Error: RIGHT and FULL OUTER JOINs are not currently supported

SELECT COUNT (DISTINCT iud) FROM (SELECT DISTINCT uid from nodes as uid UNION SELECT DISTINCT uid from ways as uid as subq);

SELECT   count (distinct nodes.uid)  from nodes  JOIN ways on nodes.uid = ways.uid ;

需要很长时间，我不确定nodes.uid =ways.uid是正确的方法

有什么想法吗？

Answer 1

我想我明白了

SELECT COUNT (DISTINCT uid) from (SELECT DISTINCT uid  from nodes  UNION SELECT  DISTINCT uid from ways) as subq ;