-- Example 1-to-1 relationship
-- PK cntry.code is FK ppl.country
SELECT cntry."name"
		,cntry.capital
		,ppl.population_growth
	FROM "IDBS01_Q12025"."Country" cntry
	INNER JOIN "IDBS01_Q12025"."Population" as ppl
		ON cntry.code = ppl.country
limit 10;


-- Example 1-to-CN relationship
-- PK cntry.code is FK brd.country1
-- without mapping table
SELECT *
	FROM "IDBS01_Q12025"."Country" cntry
	FULL OUTER JOIN "IDBS01_Q12025".borders brd
		ON cntry.code = brd.country1
	WHERE 1 = 1
		--AND brd.country1 IS NULL
		AND cntry.code IS NULL
limit 10;

-- Example 1-to-CN relationship
--how to check if it is a 1-to-N relationship

SELECT *
	FROM "IDBS01_Q12025"."Country" cntry
	LEFT JOIN "IDBS01_Q12025"."geo_Desert" gdsrt
		ON cntry.code = gdsrt.country
	LEFT JOIN "IDBS01_Q12025"."Desert" dsrt
		ON gdsrt.desert = dsrt."name"
limit 10;


--Example N-to-CM relationship
--with mapping table to N created by provicence

SELECT gm.mountain
		,count (1) AS Anzahl
	FROM "IDBS01_Q12025"."Country" cntry
	LEFT JOIN "IDBS01_Q12025"."geo_Mountain" gm
		ON cntry.code = gm.country
	group by gm.mountain
	having count(1) > 1
	order by 2 desc
;

SELECT *
	FROM "IDBS01_Q12025"."geo_Mountain"
	WHERE "geo_Mountain".mountain = 'Popocatepetl'
limit 10;

SELECT *
	FROM "IDBS01_Q12025"."Country" cntry
	INNER JOIN "IDBS01_Q12025"."Province" prv
		ON cntry.code = prv.country
	LEFT OUTER JOIN "IDBS01_Q12025"."geo_Mountain" gm
		ON prv.country = gm.country
			AND prv."name" = gm.province
limit 10;