这是我的数据库表，其中包含一些值。从 topic1 到 topic8 有不同的主题名称。 我想从所有这些值中访问不同的主题名称。 它的 sql 查询是什么？
最佳答案
使用联合查询:
select topic1 as topic from t union
select topic2 as topic from t union
select topic3 as topic from t union
select topic4 as topic from t union
select topic5 as topic from t union
select topic6 as topic from t union
select topic7 as topic from t union
select topic8 as topic from t;
如果您不需要 NULL，请包含 WHERE 子句:
select topic1 as topic from t where topic1 is not null union
select topic2 as topic from t where topic2 is not null union
select topic3 as topic from t where topic3 is not null union
select topic4 as topic from t where topic4 is not null union
select topic5 as topic from t where topic5 is not null union
select topic6 as topic from t where topic6 is not null union
select topic7 as topic from t where topic7 is not null union
select topic8 as topic from t where topic8 is not null;
关于mysql - 如何从行和列中一起选择不同的值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38187670/