例如，假设我有一个 12 行的 SQL 表，它看起来像下面左边的表，我想在右边创建聚合行数的汇总表。

这是此示例的 SQLFiddle：http ://sqlfiddle.com/#!9/ee508f/1

我可以通过以下查询分别获取这 4 个汇总列中的每一个：

SELECT Product, COUNT(*) AS bad FROM mytable WHERE Quality IN (1,2,3) GROUP BY Product;
SELECT Product, COUNT(*) AS acceptable FROM mytable WHERE Quality IN (4,5,6) GROUP BY Product;
SELECT Product, COUNT(*) AS good FROM mytable WHERE Quality IN (7,8,9) GROUP BY Product;
SELECT Product, COUNT(*) AS great FROM mytable WHERE Quality IN (10) GROUP BY Product;

但是如何将这 4 个结果合并到一个表格中，就像我的图片中显示的那样？我想要一个可以简单地添加额外列（而不是具有另一个嵌套级别）的解决方案，因为在我的实际项目中，我有 12 个这样的列并且深度嵌套，许多查询不会很可读。

回答

SELECT Product,
       SUM(CASE WHEN Quality IN (1,2,3) THEN 1
                ELSE 0
            END
          ) AS good,
       SUM(CASE WHEN Quality IN (4,5,6) THEN 1
                ELSE 0
            END
          ) AS fair,
       ...
       ...
  FROM YOUR_TABLE
 GROUP
    BY Product