如何在一个查询中选择以下数据

Question

I am using postgres

Table 1: person

Columns:: id,person_name,person_add,block_id
FK==>person(block_id) reference block(id)

Table 2: block

Columns:: id,block_name,district_id
FK==> block(district_id) reference district(id)

Table 3: district

Columns:: id,district_name,state_id
FK==> district(state_id) reference state(id)

Table 4: state

Columns:: id,state_name,country_id
FK==> state(country_id) reference country(id)

Table 5: country

Columns:: id,country_name

i have written query as follow::

When i want block wise details

SELECT p.id,p.person_name,b.block_name,d.district_name,s.state_name,c.country_name
FROM person p 
INNER JOIN block b ON b.id = p.block_id
INNER JOIN district d ON d.id = b.district_id
INNER JOIN state s ON s.id = d.state_id
INNER JOIN country c ON c.id = s.country_id
WHERE b.id = ? OR d.id = ? OR s.id = ? OR c.id = ?

how to write it in single query for following cases ???

1.i have only country id and s.id,d.id,b.id are going to be null(here above query gives fine result)

2.i have country id and state id and d.id,b.id(here it will prefer according to c.id)

3.i have country id, state id and district id b.id(same here it will prefer according to c.id)

4.i have country id,state id,district id and block id is null(same here it will prefer according to c.id)

Answer 1

If I understand correctly the criteria is optional. You may be searching for a certain country, state, district and block or for instance only for a country.

So check each variable for null. Something like this:

SELECT p.id,p.person_name,b.block_name,d.district_name,s.state_name,c.country_name
FROM person p 
INNER JOIN block b    ON b.id = p.block_id
INNER JOIN district d ON d.id = b.district_id
INNER JOIN state s    ON s.id = d.state_id 
INNER JOIN country c  ON c.id = s.country_id
WHERE (b.id = :block_id    OR :block_id is null)
  AND (d.id = :district_id OR :district_id is null)
  AND (s.id = :state_id    OR :state_id is null)
  AND (c.id = :country_id  OR :country_id is null);

(You can also move the conditions to the ON clauses; whichever you prefer.)