# SQL code generation

    * contains only *lowercase* word (\w) characters

    * doesn't start with a digit

    * contains "_", so that it's not a keyword

    '''

    return re.match(r'^(?=.*_)(?!\d)[^\WA-Z]+$', name)

        # doubling an embedded quote escapes it in both PostgreSQL and MySQL

    def __init__(self, value): self.value = value

    def __str__(self): return clean_name(strings.repr_no_u(self))

class Code(BasicObject):

    def to_str(self, db): return self.str_

    def __init__(self, expr): self.expr = expr

    def to_str(self, db): return '('+self.expr.to_str(db)+')'

    def to_str(self, db): return db.esc_value(self.value)

    if isinstance(value, Code): return value

    else: return Literal(value)

    def __init__(self, name, schema=None):

        '''

        @param schema str|None (for no schema)

        '''

        self.name = name

        self.schema = schema

        str_ = ''

        if self.schema != None: str_ += db.esc_name(self.schema)+'.'

        str_ += db.esc_name(self.name)

        return str_

    def to_Table(self): return self

    def __init__(self, name, code, cols=None):

        Table.__init__(self, name)

        if not isinstance(code, Code): code = Table(code)

        self.code = code

        self.cols = cols

    def to_str(self, db):

        return str_

    def to_Table(self): return Table(self.name)

    def __init__(self, name, table=None):

        '''

        @param table Table|None (for no table)

        '''

        self.name = name

        self.table = table

    def to_str(self, db):

        str_ = ''

        if self.table != None: str_ += self.table.to_str(db)+'.'

    def to_Col(self): return self

    '''

    @param name If not None, any non-Col input will be renamed using NamedCol.

    '''

    if name != None:

        col = as_Value(col)

        if not isinstance(col, Col): col = NamedCol(name, col)

    if isinstance(col, Code): return col

    col = as_Col(col)

    if check_table != None:

        table = col.table

        assert table == None or table == check_table

    return Col(col.name)

        self.code = code

    def to_str(self, db):

    def to_Col(self): return Col(self.name)

    if isinstance(col, NamedCol): col = col.code

    return col

    '''A dict that automatically makes inserted entries Col objects'''

    def __setitem__(self, key, value):

        return dict.__setitem__(self, key, as_Col(value, name=key))

    def update(self, dict_):

        for key, value in dict_.iteritems(): self[key] = value

class Function(Table): pass

class FunctionCall(Code):

    def __init__(self, function, *args):

        '''

        @param args [Code...] The function's arguments

        '''

        if not isinstance(function, Code): function = Function(function)

        self.function = function

        self.args = args

    def to_str(self, db):

        args_str = ', '.join((v.to_str(db) for v in self.args))

        return self.function.to_str(db)+'('+args_str+')'

    '''Wraps a value inside a function call.

    Propagates any column renaming to the returned value.

    '''

    name = None

    if isinstance(value, NamedCol): name = value.name

    value = FunctionCall(function, value)

    if name != None: value = NamedCol(name, value)

    return value

    '''Unwraps any function call to its first argument.

    Also removes any column renaming.

    '''

    func_call = remove_col_rename(func_call)

    if not isinstance(func_call, FunctionCall): return func_call

    if check_name != None:

        name = func_call.function.name

        assert name == None or name == check_name

    return func_call.args[0]

    def __init__(self, col, value):

        value = as_ValueCond(value)

        self.col = col

        self.value = value

    def to_str(self, db): return self.value.to_str(db, self.col)

    '''

    @param keyword The keyword to add before the conditions, if any

    '''

    str_ = ''

    if keyword != None:

        if conds == []: whitespace = ''

        elif len(conds) == 1: whitespace = ' '

        else: whitespace = '\n'

        str_ += keyword+whitespace

    str_ += '\nAND '.join(conds)

    return str_

        self.value = value

        raise NotImplemented()

class CompareCond(ValueCond):

    def __init__(self, value, operator='='):

        @param operator By default, compares NULL values literally. Use '~=' or

            '~!=' to pass NULLs through.

        '''

        self.operator = operator

        if not isinstance(left_value, Code): left_value = Col(left_value)

        left = left_value.to_str(db)

        right = right_value.to_str(db)

        # Parse operator

        operator = strings.remove_prefix('~', operator, passthru_null_ref)

        neg_ref = [False]

        operator = strings.remove_prefix('!', operator, neg_ref)

        equals = operator.endswith('=')

        if equals and is_null(self.value): operator = 'IS'

        # Create str

        str_ = left+' '+operator+' '+right

        if equals and not passthru_null_ref[0] and isinstance(right_value, Col):

        if neg_ref[0]: str_ = 'NOT '+str_

assume_literal = object()

def as_ValueCond(value, default_table=assume_literal):

    if not isinstance(value, ValueCond):

        if default_table is not assume_literal:

            value = as_Col(value, default_table)

        return CompareCond(value)

join_same_not_null = object()

        '''

        @param mapping dict(right_table_col=left_table_col, ...)

            * if left_table_col is join_same_not_null:

              left_table_col = right_table_col and both have NOT NULL constraint

              * Note that right_table_col must be a string

            * filter_out: equivalent to 'LEFT' with the query filtered by

              `table_pkey IS NULL` (indicating no match)

        '''

        if util.is_str(table): table = Table(table)

        assert type_ == None or util.is_str(type_) or type_ is filter_out

        self.table = table

        self.mapping = mapping

        self.type_ = type_

    def to_str(self, db, left_table):

        right_table = left_table

        left_table = self.table # note left_table is reassigned

            '''Parses non-USING joins'''

            right_table_col, left_table_col = entry

            left = right_table_col

            right = left_table_col

            elif right is join_same_not_null:

                right = CompareCond(as_Col(left, right_table), '~=')

        type_ = self.type_

            join_cond = 'USING ('+(', '.join(cols))+')'

            if len(joins) == 1: whitespace = ' '

            else: whitespace = '\n'

        # Create join

        if type_ is filter_out: type_ = 'LEFT'

        if type_ != None: str_ += type_+' '

##### Value exprs

row_count = CustomCode('count(*)')