SQL中的额外列选择查询或视图

Question

So i currently got 3 tables in my database, One containing information about members, one about their boats (length) and one about prices.

Lid (Member)

Schip (Boat)

Tarief (Prices)

I need to create a query that combines parts of these tables, but i have not found any way how to do this. This is what my 'new' table / select statement result should look like:

• Where Naam should be Lid.Naam (from the 1st table)
• Where Adres should be Lid.Adres (from the 1st table)
• Where Email should be Lid.Email (from the 1st table)
• Where contributie should be Tarief.Bedrag where Soort = 'contributie'
• Where liggeld should be (Tarief.Bedrag where Soort = 'liggeld') x (Schip.lengte) and if Lid.Schip is empty, this amount should be 0
• Where totaal should be liggeld + contributie
• At last, everyone who has lid.ContributieBetaald = 'ja' should not be in the list

I hademade an example for how it should look like if the query works completely:

If anyone knows how to create a query for this or a view and would like to help me, thanks!

Answer 1

Try this:

SELECT l.Naam, l.Adres, l.Email, 
(SELECT Bedrag FROM Tarief WHERE Soort = 'contributie' LIMIT 1) AS 'Contributie',
(SELECT Bedrag FROM Tarief WHERE Soort = 'liggeld' LIMIT 1)*IFNULL(s.length,0) AS 'Liggeld',
(SELECT Bedrag FROM Tarief WHERE Soort = 'contributie' LIMIT 1)+
(SELECT Bedrag FROM Tarief WHERE Soort = 'liggeld' LIMIT 1)*IFNULL(s.length,0)  AS 'Totaal'
FROM Lid l
LEFT JOIN Schip s ON l.Schip=s.Naam
WHERE l.ContributieBetaald <> 'ja';