mysql - 如何在 where/and 子句中使用 sql 选择数据

Question

我有这个运行良好的 mysql 代码，但我想知道如何避免两次执行 RAW 数据计算，这是我的代码

SELECT `users`.*, ( 3959 * ACOS(COS(RADIANS(43.9743)) *
  COS(RADIANS(locations.lat)) * 
  COS( RADIANS(-75.9122) - RADIANS(locations.LONG)) +
                              SIN(RADIANS(43.9743)) *
  SIN(RADIANS(locations.lat) )) ) AS distance 
FROM   `users` 
INNER JOIN `addresses` ON `users`.`id` = `addresses`.`user_id` 
LEFT JOIN `locations` ON `addresses`.`zip` = `locations`.`zip` 
WHERE  `type` = 'doctor' 
  AND ( 3959 * ACOS(COS(RADIANS(43.9743)) * COS(RADIANS(locations.lat)) *
    COS( RADIANS(-75.9122) - RADIANS(locations.LONG)) +
    SIN(RADIANS(43.9743)) * SIN(RADIANS(locations.lat) )) ) < 100
  AND `users`.`deleted_at` IS NULL 
ORDER BY distance ASC
LIMIT  15 OFFSET 0 

如您所见，我使用了两次此计算 ( 3959 * ACOS(COS(RADIANS(43.9743)) * COS(RADIANS(locations.lat)) * COS( RADIANS(-75.9122) - RADIANS(locations.LONG)) + SIN(RADIANS(43.9743)) * SIN(RADIANS(locations.lat) )) )在 AND 和 SELECT 语句上。

我试过 AND distance < 100但我收到一条错误消息，说列不存在。

感谢任何帮助

Answer 1

您可以将计算列放置在可从中访问指定列的子查询(特别是“表表达式”)中。

例如:

select *
from ( -- the definition of table expression "x" starts
  SELECT `users`.*, ( 3959 * ACOS(COS(RADIANS(43.9743)) *
    COS(RADIANS(locations.lat)) * 
    COS( RADIANS(-75.9122) - RADIANS(locations.LONG)) +
                              SIN(RADIANS(43.9743)) *
    SIN(RADIANS(locations.lat) )) ) AS distance 
  FROM   `users` 
  INNER JOIN `addresses` ON `users`.`id` = `addresses`.`user_id` 
  LEFT JOIN `locations` ON `addresses`.`zip` = `locations`.`zip` 
) x -- the definition of table expression "x" ends
WHERE `type` = 'doctor' 
  AND distance < 100 -- here we use the "distance" column
  AND `users`.`deleted_at` IS NULL 
ORDER BY distance ASC
LIMIT  15 
OFFSET 0 

在 MySQL 8.x 中，您可以使用 CTE(公用表表达式)，如:

with
x as (
  SELECT `users`.*, ( 3959 * ACOS(COS(RADIANS(43.9743)) *
    COS(RADIANS(locations.lat)) * 
    COS( RADIANS(-75.9122) - RADIANS(locations.LONG)) +
                              SIN(RADIANS(43.9743)) *
    SIN(RADIANS(locations.lat) )) ) AS distance 
  FROM   `users` 
  INNER JOIN `addresses` ON `users`.`id` = `addresses`.`user_id` 
  LEFT JOIN `locations` ON `addresses`.`zip` = `locations`.`zip` 
)
SELECT *
FROM x
WHERE  `type` = 'doctor' 
  AND distance < 100
  AND `users`.`deleted_at` IS NULL 
ORDER BY distance ASC
LIMIT  15 
OFFSET 0