cols = [type_, 'column_default',

            sql_gen.Cast('boolean', sql_gen.Col('is_nullable'))]

##### Error tracking

def track_data_error(db, errors_table, cols, value, error_code, error):

    '''

    @param errors_table If None, does nothing.

    '''

    if errors_table == None or cols == (): return

    for col in cols:

        try:

            sql.insert(db, errors_table, dict(column=col.name, value=value,

                error_code=error_code, error=error), recover=True,

                cacheable=True, log_level=4)

        except sql.DuplicateKeyException: pass

def cast(db, type_, col, errors_table=None):

    '''Casts an (unrenamed) column or value.

    If errors_table set and col has srcs, saves errors in errors_table (using

    col's srcs attr as the source columns) and converts errors to warnings.

    @param col str|sql_gen.Col|sql_gen.Literal

    @param errors_table None|sql_gen.Table|str

    '''

    col = sql_gen.as_Col(col)

    save_errors = (errors_table != None and isinstance(col, sql_gen.Col)

        and col.srcs != ())

    if not save_errors: return sql_gen.Cast(type_, col) # can't save errors

    assert not isinstance(col, sql_gen.NamedCol)

    errors_table = sql_gen.as_Table(errors_table)

    srcs = map(sql_gen.to_name_only_col, col.srcs)

    function_name = str(sql_gen.FunctionCall(type_, *srcs))

    function = db.TempFunction(function_name)

    while True:

        # Create function definition

        errors_table_cols = map(sql_gen.Col,

            ['column', 'value', 'error_code', 'error'])

        query = '''\

CREATE FUNCTION '''+function.to_str(db)+'''(value text)

RETURNS '''+type_+'''

LANGUAGE plpgsql

STRICT

AS $$

BEGIN

    /* The explicit cast to the return type is needed to make the cast happen

    inside the try block. (Implicit casts to the return type happen at the end

    of the function, outside any block.) */

    RETURN value::'''+type_+''';

EXCEPTION

    WHEN data_exception THEN

        -- Save error in errors table.

        DECLARE

            error_code text := SQLSTATE;

            error text := SQLERRM;

            "column" text;

        BEGIN

            -- Insert the value and error for *each* source column.

            FOR "column" IN

'''+sql.mk_select(db, sql_gen.NamedValues('c', None, [[c.name] for c in srcs]),

    order_by=None, start=0)+'''

            LOOP

                BEGIN

'''+sql.mk_insert_select(db, errors_table, errors_table_cols,

    sql_gen.Values(errors_table_cols).to_str(db))+''';

                EXCEPTION

                    WHEN unique_violation THEN NULL; -- continue to next row

                END;

            END LOOP;

        END;

        RAISE WARNING '%', SQLERRM;

        RETURN NULL;

END;

$$;

'''

        # Create function

        try:

            sql.run_query(db, query, recover=True, cacheable=True,

                log_ignore_excs=(sql.DuplicateException,))

            break # successful

        except sql.DuplicateException:

            function.name = sql.next_version(function.name)

            # try again with next version of name

    return sql_gen.FunctionCall(function, col)

def cast_temp_col(db, type_, col, errors_table=None):

    '''Like cast(), but creates a new column with the cast values if the input

    is a column.

    @return The new column or cast value

    '''

    def cast_(col): return cast(db, type_, col, errors_table)

    try: col = sql_gen.underlying_col(col)

    except sql_gen.NoUnderlyingTableException: return sql_gen.wrap(cast_, col)

    table = col.table

    new_col = sql_gen.Col(sql_gen.concat(col.name, '::'+type_), table, col.srcs)

    expr = cast_(col)

    # Add column

    new_typed_col = sql_gen.TypedCol(new_col.name, type_)

    sql.add_col(db, table, new_typed_col, comment='src: '+repr(col))

    new_col.name = new_typed_col.name # propagate any renaming

    sql.update(db, table, [(new_col, expr)], in_place=True, cacheable=True)

    sql.add_index(db, new_col)

    return new_col

def errors_table(db, table, if_exists=True):

    '''

    @param if_exists If set, returns None if the errors table doesn't exist

    @return None|sql_gen.Table

    '''

    table = sql_gen.as_Table(table)

    if table.srcs != (): table = table.srcs[0]

    errors_table = sql_gen.suffixed_table(table, '.errors')

    if if_exists and not sql.table_exists(db, errors_table): return None

    return errors_table

##### Import

    errors_table_ = errors_table(db, in_tables0)

        track_data_error(db, errors_table_, in_col.srcs, value,

            mapping[out_col] = cast_temp_col(db, type_, mapping[out_col],