在SQL WHERE子句中使用多个条件

Question

I have been searching online and even amongst Stackoverflow questions about this issue but couldnt receive any related response. The SQL query that I have shown below,

SELECT Scania.GensetType
    , Scania.EngineType
    , Scania.Engine60Hz
    , Scania.Alternator
    , Scania.PriceEur 
FROM Scania 
LEFT JOIN NordhavnGenset 
    ON Scania.GensetType=NordhavnGenset.Alternator 
WHERE (NordhavnGenset.MaxKva='46') 
    and (Generator.Alternator='ECP34-1LN/4') 
    and (insulation.Insulation='F (90ºC/45ºC)') 
    and (Klasse.Klasse='KRS\r') 
    and (airinletfilter.AirInletFilter='No') 
    and (Ip.IP='IP23');

Always returns the error message below, and I have checked several times that this column exists in the table!

#1054 - Unknown column 'Generator.Alternator' in 'where clause'

However if I execute the query by stopping at the first Where clause, then the results are displayed,

SELECT Scania.GensetType
    , Scania.EngineType
    , Scania.Engine60Hz
    , Scania.Alternator
    , Scania.PriceEur 
FROM Scania 
LEFT JOIN NordhavnGenset 
    ON Scania.GensetType=NordhavnGenset.Alternator 
WHERE (NordhavnGenset.MaxKva='46');

The new query

    SELECT  Scania.GensetType, Scania.EngineType, Scania.Engine60Hz, Scania.Alternator, Scania.PriceEur
FROM Scania  
LEFT JOIN NordhavnGenset
    ON Scania.GensetType=NordhavnGenset.Alternator 
LEFT JOIN Generator
    ON Scania.Alternator=Generator.Alternator
LEFT JOIN Insulation 
    ON NordhavnGenset.Insulation=Insulation.Insulation
LEFT JOIN Klasse
    ON NordhavnGenset.Class=Klasse.Class
LEFT JOIN AirInletFilter
    ON NordhavnGenset.AirInletFilter=AirInletFilter.AirInletFilter
LEFT JOIN IP
    ON NordhavnGenset.Ip=IP.IP
WHERE (NordhavnGenset.MaxKva='46') and (Generator.Alternator='ECP34-1LN/4') and (Insulation.Insulation='F (90ºC/45ºC)') and (Klasse.Klasse='KRS\r') and (AirInletFilter.AirInletFilter='No') and (IP.IP='IP23');

Answer 1

It does not appear that you are Joining on a table called Generator . You cannot have the table in your WHERE clause unless you JOIN on it.

If you add a JOIN to Generator then you can use it in the WHERE clause.

SELECT *
FROM Scania 
LEFT JOIN NordhavnGenset 
    ON Scania.GensetType=NordhavnGenset.Alternator 
LEFT JOIN Generator 
    ON ....
WHERE (Generator.Alternator='ECP34-1LN/4') ...

You also have other tables in your WHERE clause that are not JOINed on, so you will need to add those as well.

Answer 2

The reason for the error is that you are not joining the tables that you are using in the WHERE clause.

The following would always give an error -

and (Generator.Alternator='ECP34-1LN/4') 
and (insulation.Insulation='F (90ºC/45ºC)') 
and (Klasse.Klasse='KRS\r') 
and (airinletfilter.AirInletFilter='No') 
and (Ip.IP='IP23');

You either need to have the table joined or the alias of the table should be the name before the '.'.

Answer 3

You're not including the Generator table in the join. Either add it, or you may mean NordhavnGenset.Alternator instead of Generator.Alternator