如何在MySQL中将多个列的值组合成一个SQL查询？

Question

假设我有以下内容：

swim_names, football_names, soccer_names, swim_age
John, Johnny, Johnson, 5
Mike, Michael, Mike, 2
Jo, Joe, Joey, 7

如何构建SQL查询，以便我可以在下面获得以下输出：

names, age
John, 5
Johnny, null
Johnson, null
Mike, 2
Michael, null
Mike, null
Jo, 7
Joe, null
Joey, null

请注意：

1. 名称是所有三个＆＃34; _names＆＃34;的名称。列
2. swim_age仅适用于＆＃34; swim_names＆＃34;
中的名称

Answer 1

尝试使用UNION ALL之类的：

 SELECT swim_names as Names, swim_age as age FROM tbl
 UNION ALL
 SELECT football_names as Names, null as age FROM tbl
 UNION ALL
 SELECT soccer_names as Names, null as age FROM tbl