Re: SELECT only those values of table B which have a value in table A

[Stefan Schwarzer <stefan.schwarzer@xxxxxxxxxxxx>]

SELECT

COALESCE(r.name, '''') AS name,

d.year_start AS year,

SUM(d.value * d_nom.value) / SUM(d_nom.value) AS value

FROM

pop_total_access_water AS d

RIGHT JOIN

countries_view AS c ON c.id = d.id_country

RIGHT JOIN

pop_total AS d_nom ON d_nom.id_country = d.id_country

RIGHT JOIN

subregions_view AS r ON r.id = c.sreg_id

WHERE

(d.year_start = 1990 ) AND

(d_nom.year_start = 1990 ) AND

d_nom.value <> 0

GROUP BY

r.name, d.year_start

ORDER BY 1,2

Now, I would like to use from table "d_nom" only these countries

which have a value in table "d" as well.

Without thinking much (so this may be completely wrong for some reason/additional
changes may be needed), why do you use a right join to the d_nom table?
An ordinary inner join should give you only these countries which have
their rows in the d table.

Thanks for that. Ok, tried that, didn't work. But gave me the go into the right direction. Stripped down the query to the absolute necessary, on a country basis, and realized that I have in some tables NULL values. So, the correct SQL is then (with the added line: (d.value IS NOT NULL )):

SELECT COALESCE(r.name, '''') AS name, d.year_start AS year, SUM(d.value * d_nom.value) / SUM(d_nom.value) AS value FROM pop_total_access_water AS d RIGHT JOIN countries_view AS c ON c.id = d.id_country RIGHT JOIN pop_total AS d_nom ON d_nom.id_country = d.id_country RIGHT JOIN subregions_view AS r ON r.id = c.sreg_id WHERE (d.year_start = 1990 ) AND (d.value IS NOT NULL ) AND (d_nom.year_start = 1990 ) AND d_nom.value <> 0 GROUP BY r.name, d.year_start ORDER BY 1,2

Thanks a lot!

Stef

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