我可以在Postgres中爲WHERE條件創建一個別名嗎？

Question

我想找到所有符合特定標準的員工的公司，並返回有關這些員工的信息，以及這些公司的所有者。不過，我的SQL有點重複，我想知道是否有一種方法可以爲我的某些WHERE條件使用別名。

考慮這個查詢：

SELECT json_agg(employee.*) employees_and_admins, company.* 
    FROM company 
    JOIN employee ON employee.company_id = company.id 
    WHERE employee.owner IS TRUE 
     -- This is where the repetitive stuff starts 
     OR employee.first_name IS NULL 
     OR employee.last_name IS NULL 
     OR employee.date_of_birth IS NULL 
     OR employee.hire_date IS NULL 
     OR employee.email IS NULL 
    GROUP BY company.id 
    HAVING sum(CASE 
     -- Note the repetition; note also we're not checking employee.owner here 
     WHEN (
      employee.first_name IS NULL 
      OR employee.last_name IS NULL 
      OR employee.date_of_birth IS NULL 
      OR employee.hire_date IS NULL 
      OR employee.email IS NULL) 
     THEN 1 ELSE 0 END) > 0; 

是否有某種方式來避免重複所有這些OR條件？有人聽說在網上搜索答案，因爲我不斷收到有關SELECT別名的信息。

Answer 1

lateral和方便bool_or：

select json_agg(employee.*) employees_and_admins, company.* 
from 
    company 
    inner join 
    employee on employee.company_id = company.id 
    cross join lateral (
     select 
      employee.first_name is null 
      or employee.last_name is null 
      or employee.date_of_birth is null 
      or employee.hire_date is null 
      or employee.email is null 
      as any_null 
    ) cjl 
where employee.owner or any_null 
group by company.id 
having bool_or(any_null) 

的替代橫向是嵌套查詢。

Answer 2

您可以創建一個函數以提高可讀性（這實際上不會影響性能），例如，

CREATE OR REPLACE FUNCTION has_a_null_value(e employee) 
RETURNS boolean LANGUAGE SQL AS $$ 
    SELECT 
     e.first_name IS NULL 
     OR e.last_name IS NULL 
     OR e.date_of_birth IS NULL 
     OR e.hire_date IS NULL 
     OR e.email IS NULL 
$$; 

SELECT json_agg(employee.*) employees_and_admins, company.* 
    FROM company 
    JOIN employee ON employee.company_id = company.id 
    WHERE employee.owner OR has_a_null_value(employee) 
    GROUP BY company.id 
    HAVING sum(has_a_null_value(employee)::int) > 0;