在 PostgreSQL 的 WHERE 子句中使用函数结果

Question

我试图在where子句中使用函数执行的结果，但没有成功：

SELECT clinics.*, distance_between_objects(1, id, 7, 3) AS dist FROM clinics WHERE dist<=1;

给我：Column "dist" does not exists。引用它就像：

SELECT clinics.*, distance_between_objects(1, id, 7, 3) AS dist FROM clinics WHERE "dist"<=1;

也没有帮助。请告知Postgres是否有可能在WHERE子句中使用函数结果而不调用它两次？谢谢！

Answer 1

为避免调用distance_between_objects两次：

--Subquery
SELECT * FROM (
    SELECT 
        *, 
        distance_between_objects(1, id, 7, 3) AS dist 
    FROM 
        clinics) AS clinics_dist 
WHERE 
    dist <= 1;

--CTE
WITH clinics_dist AS (
    SELECT 
        *, 
        distance_between_objects(1, id, 7, 3) AS dist 
    FROM 
        clinics
)
SELECT 
    * 
FROM 
    clinics_dist 
WHERE 
    dist <= 1;

CTE我认为这是一种更干净的方法。