SQL

Join base on multiple or conditions

FROM Table1 t
INNER JOIN Table2 s ON case
  when t.number = s.number then 1
  when t.letter = s.letter then 1
  else 0 end = 1

Join base on multiple and conditions

var query = from t1 in context.table1
            join t2 in context.table2 on new {t1.fieldA, t1.fieldB} equals new {t2.fieldA, t2.fieldB}
            join t3 in context.table3 on t3.fieldA equals t3.fieldC
            where 
                t1.Enabled == 1 && t2.Active == 1 && t3.Linked == 1 ...