Question

第一个代码无法在MonetDB中执行：

   SELECT rc0.id as runcat, x0.id as xrtcat
    FROM extractedcatalog x0 
    INNER JOIN image i0
          ON i0.id = 1 AND i0.id = x0.image
    INNER JOIN runningcatalog rc0
                 ON rc0.zone BETWEEN x0.zone-1
                                  AND x0.zone+1
                 AND rc0.wm_decl BETWEEN x0.decl - i0.rb_smaj
                                     AND x0.decl + i0.rb_smaj
                 AND rc0.x*x0.x +rc0.y*x0.y +rc0.z*x0.z >cos(radians(i0.rb_smaj));

连接已终止！

但是下面的代码可以很快执行，为什么????

SELECT rc0.id as runcat, x0.id as xrtcat
FROM extractedcatalog x0 
INNER JOIN image i0
      ON i0.id = 1 AND i0.id = x0.image
INNER JOIN runningcatalog rc0
             ON rc0.zone BETWEEN x0.zone-1
                              AND x0.zone+1
             AND rc0.wm_decl BETWEEN x0.decl - i0.rb_smaj
                                 AND x0.decl + i0.rb_smaj
             AND rc0.x*x0.x +rc0.y*x0.y +rc0.z*x0.z >cos(radians(0.0055));

在表格图片中，只有一行：id = 1，rb_smaj = 0.0055。非常感谢！

Answer 1

如果唯一的区别是cos，请将此数字保存为数据库字段并在其上添加索引。

Answer 2

不同之处在于第一个查询在每个行加入时执行cos()（可能是数百万次执行，具体取决于行数限定），但第二个执行`cos（）对于整个查询只需一次，所以很多更快。

如果您希望第一个查询快速执行，请尝试将条件移动到WHERE子句，以便cos()每行image只需一次：

SELECT rc0.id as runcat, x0.id as xrtcat
FROM extractedcatalog x0 
INNER JOIN image i0
      ON i0.id = 1 AND i0.id = x0.image
INNER JOIN runningcatalog rc0
    ON rc0.zone BETWEEN x0.zone-1 AND x0.zone+1
    AND rc0.wm_decl BETWEEN x0.decl - i0.rb_smaj AND x0.decl + i0.rb_smaj
WHERE rc0.x*x0.x +rc0.y*x0.y +rc0.z*x0.z > cos(radians(i0.rb_smaj))

如果这不起作用，请尝试创建内部查询以选择条件中包含的列加上cos()结果，并在其上放置where子句。

下一个代码之间有什么区别？

2 个答案: