java - 执行多个select语句

Question

我想使用GROUP BY执行多个选择语句。

我尝试过以下一种:

ResultSet rs=s.executeQuery("SELECT attr_name, count(*)"
                          + " FROM Table_name"
                          + " GROUP BY attr_name;"
                          + "SELECT attr_name, count(*)"
                          + " FROM Table_name"
                          + " GROUP BY attr_name");

但它不会来。

Answer 1

连接两组结果的方法是使用UNION ALL

ResultSet rs=s.executeQuery(
  "select attr_name,count(*) from Table_name group by attr_name UNION ALL select attr_name,count(*) from Table_name group by attr_name"
);

请小心确保列相同:列数必须相同并且类型必须相同。还值得显式命名列以确保:SELECT attr_name, count(*) AS attr_count FROM...