SQL Syntax Error Group By - sql

Question

I've got a sql syntax and it gives me the error:
Msg 8120, Level 16, State 1, Line 1 Column 'VEHICLEMASTR.cconduction'
is invalid in the select list because it is not contained in either an
aggregate function or the GROUP BY clause.
Here is the SQL syntax:
SELECT A.cplateno,A.cconduction,A.cname,A.cbatterymodel
,A.dbattery,A.DlastChange,A.nlastoilkm,A.naveragekmday
,A.dkmreading,A.dfranacq,A.dfranexp,A.nlimit,A.dreading
,CONVERT(varchar(2),month(MAX(B.dinsexp)))+'/'+CONVERT(varchar(2),day(MAX(B.dinsexp)))+'/'+CONVERT(varchar(4),year(MAX(B.dinsexp))) as dinsexp
,C.corno,CONVERT(varchar(2),month(MAX(C.dregexp)))+'/'+CONVERT(varchar(2),day(MAX(C.dregexp)))+'/'+ CONVERT(varchar(4),year(MAX(C.dregexp))) as dregexp
FROM VEHICLEMASTR A
LEFT JOIN VEHICLEINSURANCE B
ON A.cplateno = B.cplateno
LEFT JOIN VREGISTRATION C
ON A.cplateno = C.cplateno
GROUP BY A.cplateno
Can anybody tell what went wrong?

Answer 1

The "group by" clause must name every column selected, except those columns that are aggregate functions.
FYI an "aggregate" function is one that returns a single value for many rows, like sum(), count(), etc

Answer 2

a.cconduction needs to be in the group by clause.
When using a Group By clause, a column must either have an aggregate function (i.e. COUNT) or be defined in the group by.
A sample group by statement with multiple grouping:
SELECT column1_name, column2_name, aggregate_function(column_name3)
FROM table_name
WHERE column_name1 operator value
GROUP BY column_name1, column_name2;

Answer 3

You must include all fields that you mentioned in your select except the column that has aggregate function so in your case it would be:
GROUP BY
a.cplateno, a.cconduction,a.cname,a.cbatterymodel,a.dbattery,
a.DlastChange,a.nlastoilkm,a.naveragekmday,
a.dkmreading,a.dfranacq,a.dfranexp,a.nlimit,a.dreading
instead of
GROUP BY a.cplateno
Edit:
If you want only the a.cplateno then you don't include the rest of the fields except aggregate function and a.cplateno like:
SELECT A.cplateno
,CONVERT(varchar(2),month(MAX(B.dinsexp)))+'/'+CONVERT(varchar(2),day(MAX(B.dinsexp)))+'/'+CONVERT(varchar(4),year(MAX(B.dinsexp))) as dinsexp
,CONVERT(varchar(2),month(MAX(C.dregexp)))+'/'+CONVERT(varchar(2),day(MAX(C.dregexp)))+'/'+ CONVERT(varchar(4),year(MAX(C.dregexp))) as dregexp
FROM VEHICLEMASTR A
LEFT JOIN VEHICLEINSURANCE B
ON A.cplateno = B.cplateno
LEFT JOIN VREGISTRATION C
ON A.cplateno = C.cplateno
GROUP BY A.cplateno