presto-main/src/main/java/io/prestosql/sql/relational/SqlToRowExpressionTranslator.java/SqlToRowExpressionTranslator/visitVariableReference
class SqlToRowExpressionTranslator:            @Override
            public RowExpression visitVariableReference(VariableReferenceExpression reference, Void context)
            {
                return new VariableReferenceExpression(reference.getName(), targetType);
            }