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。像这样引用它：

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

也无济于事。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

可以在where子句中使用函数：

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

Answer 2

为了避免调用 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 在我看来是一种更简洁的方法。

Answer 3

您也可以使用 LATERAL

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

在 PostgreSQL 的 WHERE 子句中使用函数结果

Using function result in WHERE clause in PostgreSQL

postgresql

select

where-clause

sql-function