queries.js

class Statement {
    constructor( state ){
        this.state = state || [];
    }

    toString(){
        return this.state
                    .map( part => part.toString() )
                    .join( '\n' );
    }
}

function statement( parts ){
    const partNames = Object.keys( parts ),
            constructors = Object.values( parts );

    class TheStatement extends Statement {}

    partNames.forEach( ( name, i ) => {
        TheStatement.prototype[ name ] = function( ...args ){
            const state = this.state.slice(),
                part = state[ i ] || ( state[ i ] = new constructors[ i ]() );
        
            state[ i ] = part.append( args );
            
            return new TheStatement( state );
        }
    });

    return ( ...args ) => {
        const statement = new TheStatement();
        return statement[ partNames[ 0 ]]( args );
    };
}

class Concatenator {
    constructor( state ){
        this.state = state || [];
    }

    append( args ){
        return new this.constructor( [ ...this.state, ...args ] );
    }
}

function all( prefix, separator, map = x => String( x ) ){
    return class extends Concatenator {
        toString(){
            return `${prefix} ${this.state.map( map ).join( ' ' + separator + ' ')}`
        }
    }
}

function last( name ){
    return class extends Concatenator {
        toString(){
            return name + ' ' + this.state[ this.state.length - 1 ];
        }
    }
}

/* This code above doesn't make any sense, isn't it?
Now, watch: */

const select = statement({
    select : all( 'SELECT', ',' ),
    from : all( 'FROM', ',', x => (
        typeof x === 'string' ? x :
        '(\n' + x.toString( ) + '\n)' 
    )),
    where : all( 'WHERE', 'AND', x => `(${x})` ),
    groupBy : all( 'GROUP BY', ',' ),
    orderBy : all( 'ORDER BY', ',' ),
    limit : last( 'LIMIT' ),
    offset : last( 'OFFSET' )
})


const a = select( 'name', 'address' )
    .from( 'users', 'addresses' )
    .where( 'users.id = addresses.user_id');

const b = a.from( select( 'name as country').from( 'countries') )
    .where( 'users.active = TRUE' );

console.log(
    a.toString()
);

console.log(
    b.toString()
);