SQL查询输出不符合预期

Question

我刚接触SQL。感谢您的耐心等候。

我的查询如下：

SELECT
    population. "District.Name",
    sum(population. "Number") AS "Total Pop",
    sum(unemployment. "Number") AS "Total Unemployment"
FROM
    population
    FULL JOIN unemployment ON population. "District.Code" = unemployment. "District Code"
WHERE
    population. "Year" = 2017
GROUP BY
    population. "District.Name",
    population. "Number",
    unemployment. "Number"
ORDER BY
    sum(unemployment. "Number") ASC

;

但是，生成的输出如所附的屏幕快照所示：

。

我想获取每个地区的总流行/总失业人数，而不是当前的情况。 我还试图找出是什么引起了地区名称的分裂。我尝试了各种组合，但尚未获得理想的结果。 有什么建议吗？预先感谢。

Answer 1

您可以在下面尝试-您无需在分组依据中添加population. "Number", unemployment. "Number"列，因为您正在这些列上使用汇总

SELECT
    population. "District.Name",
    sum(population. "Number") AS "Total Pop",
    sum(unemployment. "Number") AS "Total Unemployment"
FROM
    population
    FULL JOIN unemployment ON population. "District.Code" = unemployment. "District Code"
WHERE
    population. "Year" = 2017
GROUP BY
    population. "District.Name",
ORDER BY
    sum(unemployment. "Number") 

Answer 2

您只需要按District.Name分组。由于您已按“人口和失业”进行分组，因此它们还将显示唯一的行。

希望这行得通！

SELECT
population. "District.Name",
sum(population. "Number") AS "Total Pop",
sum(unemployment. "Number") AS "Total Unemployment"
FROM
population FULL JOIN unemployment ON population. "District.Code" = unemployment. "District Code"
WHERE
population. "Year" = 2017
GROUP BY
population. "District.Name",
ORDER BY
sum(unemployment. "Number") ASC

Answer 3

FULL JOIN几乎不再需要，当然对于带有WHERE子句的查询也不需要。我怀疑INNER JOIN足够。

但是您将获得多行。这表明在JOIN之后的 处进行汇总将使某些事情变得多余。汇总之前做JOIN：

SELECT p."District.Name", p."Total Pop",
       u."Total Unemployment",
       (p."Total Pop" * 1.0 / u."Total Unemployment") as ratio
FROM (SELECT p."District.Name", SUM(p."Number") AS "Total Pop"
      FROM population p
      WHERE p."Year" = 2017
      GROUP BY p."District.Name"
     ) p INNER JOIN
     (SELECT u."District.Name", SUM(u."Number") AS "Total Unemployment"
      FROM unemployment u
      GROUP BY u."District.Name"
     ) u
     ON p."District.Code" = u."District Code"
ORDER BY u."Total Unemployment" ASC;

我怀疑您的人数仍然不会达到您的期望，因为您只针对人口筛选年份。我怀疑两个数字都应具有相似的过滤器。如果是这种情况，请询问另一个问题。提供样本数据和所需结果。

在样式方面：

• 不要在列别名中放置空格。
• 除非您别无选择，否则绝对不要放置句点。
• 也就是说，创建不需要定界符的列和表别名-编写和读取查询要容易得多。
• 使用简单的表别名。