sqlglot.transforms API documentation

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# sqlglot.transforms

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      1from __future__ import annotations
      2
      3import typing as t
      4
      5from sqlglot import expressions as exp
      6from sqlglot.helper import find_new_name, name_sequence
      7
      8if t.TYPE_CHECKING:
      9    from sqlglot.generator import Generator
     10
     11
     12def unalias_group(expression: exp.Expression) -> exp.Expression:
     13    """
     14    Replace references to select aliases in GROUP BY clauses.
     15
     16    Example:
     17        >>> import sqlglot
     18        >>> sqlglot.parse_one("SELECT a AS b FROM x GROUP BY b").transform(unalias_group).sql()
     19        'SELECT a AS b FROM x GROUP BY 1'
     20
     21    Args:
     22        expression: the expression that will be transformed.
     23
     24    Returns:
     25        The transformed expression.
     26    """
     27    if isinstance(expression, exp.Group) and isinstance(expression.parent, exp.Select):
     28        aliased_selects = {
     29            e.alias: i
     30            for i, e in enumerate(expression.parent.expressions, start=1)
     31            if isinstance(e, exp.Alias)
     32        }
     33
     34        for group_by in expression.expressions:
     35            if (
     36                isinstance(group_by, exp.Column)
     37                and not group_by.table
     38                and group_by.name in aliased_selects
     39            ):
     40                group_by.replace(exp.Literal.number(aliased_selects.get(group_by.name)))
     41
     42    return expression
     43
     44
     45def eliminate_distinct_on(expression: exp.Expression) -> exp.Expression:
     46    """
     47    Convert SELECT DISTINCT ON statements to a subquery with a window function.
     48
     49    This is useful for dialects that don't support SELECT DISTINCT ON but support window functions.
     50
     51    Args:
     52        expression: the expression that will be transformed.
     53
     54    Returns:
     55        The transformed expression.
     56    """
     57    if (
     58        isinstance(expression, exp.Select)
     59        and expression.args.get("distinct")
     60        and expression.args["distinct"].args.get("on")
     61        and isinstance(expression.args["distinct"].args["on"], exp.Tuple)
     62    ):
     63        distinct_cols = expression.args["distinct"].pop().args["on"].expressions
     64        outer_selects = expression.selects
     65        row_number = find_new_name(expression.named_selects, "_row_number")
     66        window = exp.Window(this=exp.RowNumber(), partition_by=distinct_cols)
     67        order = expression.args.get("order")
     68
     69        if order:
     70            window.set("order", order.pop().copy())
     71
     72        window = exp.alias_(window, row_number)
     73        expression.select(window, copy=False)
     74
     75        return exp.select(*outer_selects).from_(expression.subquery()).where(f'"{row_number}" = 1')
     76
     77    return expression
     78
     79
     80def eliminate_qualify(expression: exp.Expression) -> exp.Expression:
     81    """
     82    Convert SELECT statements that contain the QUALIFY clause into subqueries, filtered equivalently.
     83
     84    The idea behind this transformation can be seen in Snowflake's documentation for QUALIFY:
     85    https://docs.snowflake.com/en/sql-reference/constructs/qualify
     86
     87    Some dialects don't support window functions in the WHERE clause, so we need to include them as
     88    projections in the subquery, in order to refer to them in the outer filter using aliases. Also,
     89    if a column is referenced in the QUALIFY clause but is not selected, we need to include it too,
     90    otherwise we won't be able to refer to it in the outer query's WHERE clause.
     91    """
     92    if isinstance(expression, exp.Select) and expression.args.get("qualify"):
     93        taken = set(expression.named_selects)
     94        for select in expression.selects:
     95            if not select.alias_or_name:
     96                alias = find_new_name(taken, "_c")
     97                select.replace(exp.alias_(select, alias))
     98                taken.add(alias)
     99
    100        outer_selects = exp.select(*[select.alias_or_name for select in expression.selects])
    101        qualify_filters = expression.args["qualify"].pop().this
    102
    103        select_candidates = exp.Window if expression.is_star else (exp.Window, exp.Column)
    104        for expr in qualify_filters.find_all(select_candidates):
    105            if isinstance(expr, exp.Window):
    106                alias = find_new_name(expression.named_selects, "_w")
    107                expression.select(exp.alias_(expr, alias), copy=False)
    108                column = exp.column(alias)
    109
    110                if isinstance(expr.parent, exp.Qualify):
    111                    qualify_filters = column
    112                else:
    113                    expr.replace(column)
    114            elif expr.name not in expression.named_selects:
    115                expression.select(expr.copy(), copy=False)
    116
    117        return outer_selects.from_(expression.subquery(alias="_t")).where(qualify_filters)
    118
    119    return expression
    120
    121
    122def remove_precision_parameterized_types(expression: exp.Expression) -> exp.Expression:
    123    """
    124    Some dialects only allow the precision for parameterized types to be defined in the DDL and not in
    125    other expressions. This transforms removes the precision from parameterized types in expressions.
    126    """
    127    for node in expression.find_all(exp.DataType):
    128        node.set(
    129            "expressions", [e for e in node.expressions if not isinstance(e, exp.DataTypeSize)]
    130        )
    131
    132    return expression
    133
    134
    135def unnest_to_explode(expression: exp.Expression) -> exp.Expression:
    136    """Convert cross join unnest into lateral view explode (used in presto -> hive)."""
    137    if isinstance(expression, exp.Select):
    138        for join in expression.args.get("joins") or []:
    139            unnest = join.this
    140
    141            if isinstance(unnest, exp.Unnest):
    142                alias = unnest.args.get("alias")
    143                udtf = exp.Posexplode if unnest.args.get("ordinality") else exp.Explode
    144
    145                expression.args["joins"].remove(join)
    146
    147                for e, column in zip(unnest.expressions, alias.columns if alias else []):
    148                    expression.append(
    149                        "laterals",
    150                        exp.Lateral(
    151                            this=udtf(this=e),
    152                            view=True,
    153                            alias=exp.TableAlias(this=alias.this, columns=[column]),  # type: ignore
    154                        ),
    155                    )
    156
    157    return expression
    158
    159
    160def explode_to_unnest(expression: exp.Expression) -> exp.Expression:
    161    """Convert explode/posexplode into unnest (used in hive -> presto)."""
    162    if isinstance(expression, exp.Select):
    163        from sqlglot.optimizer.scope import Scope
    164
    165        taken_select_names = set(expression.named_selects)
    166        taken_source_names = {name for name, _ in Scope(expression).references}
    167
    168        for select in expression.selects:
    169            to_replace = select
    170
    171            pos_alias = ""
    172            explode_alias = ""
    173
    174            if isinstance(select, exp.Alias):
    175                explode_alias = select.alias
    176                select = select.this
    177            elif isinstance(select, exp.Aliases):
    178                pos_alias = select.aliases[0].name
    179                explode_alias = select.aliases[1].name
    180                select = select.this
    181
    182            if isinstance(select, (exp.Explode, exp.Posexplode)):
    183                is_posexplode = isinstance(select, exp.Posexplode)
    184
    185                explode_arg = select.this
    186                unnest = exp.Unnest(expressions=[explode_arg.copy()], ordinality=is_posexplode)
    187
    188                # This ensures that we won't use [POS]EXPLODE's argument as a new selection
    189                if isinstance(explode_arg, exp.Column):
    190                    taken_select_names.add(explode_arg.output_name)
    191
    192                unnest_source_alias = find_new_name(taken_source_names, "_u")
    193                taken_source_names.add(unnest_source_alias)
    194
    195                if not explode_alias:
    196                    explode_alias = find_new_name(taken_select_names, "col")
    197                    taken_select_names.add(explode_alias)
    198
    199                    if is_posexplode:
    200                        pos_alias = find_new_name(taken_select_names, "pos")
    201                        taken_select_names.add(pos_alias)
    202
    203                if is_posexplode:
    204                    column_names = [explode_alias, pos_alias]
    205                    to_replace.pop()
    206                    expression.select(pos_alias, explode_alias, copy=False)
    207                else:
    208                    column_names = [explode_alias]
    209                    to_replace.replace(exp.column(explode_alias))
    210
    211                unnest = exp.alias_(unnest, unnest_source_alias, table=column_names)
    212
    213                if not expression.args.get("from"):
    214                    expression.from_(unnest, copy=False)
    215                else:
    216                    expression.join(unnest, join_type="CROSS", copy=False)
    217
    218    return expression
    219
    220
    221def remove_within_group_for_percentiles(expression: exp.Expression) -> exp.Expression:
    222    if (
    223        isinstance(expression, exp.WithinGroup)
    224        and isinstance(expression.this, (exp.PercentileCont, exp.PercentileDisc))
    225        and isinstance(expression.expression, exp.Order)
    226    ):
    227        quantile = expression.this.this
    228        input_value = t.cast(exp.Ordered, expression.find(exp.Ordered)).this
    229        return expression.replace(exp.ApproxQuantile(this=input_value, quantile=quantile))
    230
    231    return expression
    232
    233
    234def add_recursive_cte_column_names(expression: exp.Expression) -> exp.Expression:
    235    if isinstance(expression, exp.With) and expression.recursive:
    236        next_name = name_sequence("_c_")
    237
    238        for cte in expression.expressions:
    239            if not cte.args["alias"].columns:
    240                query = cte.this
    241                if isinstance(query, exp.Union):
    242                    query = query.this
    243
    244                cte.args["alias"].set(
    245                    "columns",
    246                    [exp.to_identifier(s.alias_or_name or next_name()) for s in query.selects],
    247                )
    248
    249    return expression
    250
    251
    252def epoch_cast_to_ts(expression: exp.Expression) -> exp.Expression:
    253    if (
    254        isinstance(expression, (exp.Cast, exp.TryCast))
    255        and expression.name.lower() == "epoch"
    256        and expression.to.this in exp.DataType.TEMPORAL_TYPES
    257    ):
    258        expression.this.replace(exp.Literal.string("1970-01-01 00:00:00"))
    259
    260    return expression
    261
    262
    263def preprocess(
    264    transforms: t.List[t.Callable[[exp.Expression], exp.Expression]],
    265) -> t.Callable[[Generator, exp.Expression], str]:
    266    """
    267    Creates a new transform by chaining a sequence of transformations and converts the resulting
    268    expression to SQL, using either the "_sql" method corresponding to the resulting expression,
    269    or the appropriate `Generator.TRANSFORMS` function (when applicable -- see below).
    270
    271    Args:
    272        transforms: sequence of transform functions. These will be called in order.
    273
    274    Returns:
    275        Function that can be used as a generator transform.
    276    """
    277
    278    def _to_sql(self, expression: exp.Expression) -> str:
    279        expression_type = type(expression)
    280
    281        expression = transforms[0](expression.copy())
    282        for t in transforms[1:]:
    283            expression = t(expression)
    284
    285        _sql_handler = getattr(self, expression.key + "_sql", None)
    286        if _sql_handler:
    287            return _sql_handler(expression)
    288
    289        transforms_handler = self.TRANSFORMS.get(type(expression))
    290        if transforms_handler:
    291            # Ensures we don't enter an infinite loop. This can happen when the original expression
    292            # has the same type as the final expression and there's no _sql method available for it,
    293            # because then it'd re-enter _to_sql.
    294            if expression_type is type(expression):
    295                raise ValueError(
    296                    f"Expression type {expression.__class__.__name__} requires a _sql method in order to be transformed."
    297                )
    298
    299            return transforms_handler(self, expression)
    300
    301        raise ValueError(f"Unsupported expression type {expression.__class__.__name__}.")
    302
    303    return _to_sql

def unalias_group( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

    13def unalias_group(expression: exp.Expression) -> exp.Expression:
    14    """
    15    Replace references to select aliases in GROUP BY clauses.
    16
    17    Example:
    18        >>> import sqlglot
    19        >>> sqlglot.parse_one("SELECT a AS b FROM x GROUP BY b").transform(unalias_group).sql()
    20        'SELECT a AS b FROM x GROUP BY 1'
    21
    22    Args:
    23        expression: the expression that will be transformed.
    24
    25    Returns:
    26        The transformed expression.
    27    """
    28    if isinstance(expression, exp.Group) and isinstance(expression.parent, exp.Select):
    29        aliased_selects = {
    30            e.alias: i
    31            for i, e in enumerate(expression.parent.expressions, start=1)
    32            if isinstance(e, exp.Alias)
    33        }
    34
    35        for group_by in expression.expressions:
    36            if (
    37                isinstance(group_by, exp.Column)
    38                and not group_by.table
    39                and group_by.name in aliased_selects
    40            ):
    41                group_by.replace(exp.Literal.number(aliased_selects.get(group_by.name)))
    42
    43    return expression

Replace references to select aliases in GROUP BY clauses.

###### Example:

>     >>> import sqlglot
>     >>> sqlglot.parse_one("SELECT a AS b FROM x GROUP BY b").transform(unalias_group).sql()
>     'SELECT a AS b FROM x GROUP BY 1'

###### Arguments:

- expression: the expression that will be transformed.

###### Returns:

> The transformed expression.

def eliminate_distinct_on( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

    46def eliminate_distinct_on(expression: exp.Expression) -> exp.Expression:
    47    """
    48    Convert SELECT DISTINCT ON statements to a subquery with a window function.
    49
    50    This is useful for dialects that don't support SELECT DISTINCT ON but support window functions.
    51
    52    Args:
    53        expression: the expression that will be transformed.
    54
    55    Returns:
    56        The transformed expression.
    57    """
    58    if (
    59        isinstance(expression, exp.Select)
    60        and expression.args.get("distinct")
    61        and expression.args["distinct"].args.get("on")
    62        and isinstance(expression.args["distinct"].args["on"], exp.Tuple)
    63    ):
    64        distinct_cols = expression.args["distinct"].pop().args["on"].expressions
    65        outer_selects = expression.selects
    66        row_number = find_new_name(expression.named_selects, "_row_number")
    67        window = exp.Window(this=exp.RowNumber(), partition_by=distinct_cols)
    68        order = expression.args.get("order")
    69
    70        if order:
    71            window.set("order", order.pop().copy())
    72
    73        window = exp.alias_(window, row_number)
    74        expression.select(window, copy=False)
    75
    76        return exp.select(*outer_selects).from_(expression.subquery()).where(f'"{row_number}" = 1')
    77
    78    return expression

Convert SELECT DISTINCT ON statements to a subquery with a window function.

This is useful for dialects that don't support SELECT DISTINCT ON but support window functions.

###### Arguments:

- expression: the expression that will be transformed.

###### Returns:

> The transformed expression.

def eliminate_qualify( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

     81def eliminate_qualify(expression: exp.Expression) -> exp.Expression:
     82    """
     83    Convert SELECT statements that contain the QUALIFY clause into subqueries, filtered equivalently.
     84
     85    The idea behind this transformation can be seen in Snowflake's documentation for QUALIFY:
     86    https://docs.snowflake.com/en/sql-reference/constructs/qualify
     87
     88    Some dialects don't support window functions in the WHERE clause, so we need to include them as
     89    projections in the subquery, in order to refer to them in the outer filter using aliases. Also,
     90    if a column is referenced in the QUALIFY clause but is not selected, we need to include it too,
     91    otherwise we won't be able to refer to it in the outer query's WHERE clause.
     92    """
     93    if isinstance(expression, exp.Select) and expression.args.get("qualify"):
     94        taken = set(expression.named_selects)
     95        for select in expression.selects:
     96            if not select.alias_or_name:
     97                alias = find_new_name(taken, "_c")
     98                select.replace(exp.alias_(select, alias))
     99                taken.add(alias)
    100
    101        outer_selects = exp.select(*[select.alias_or_name for select in expression.selects])
    102        qualify_filters = expression.args["qualify"].pop().this
    103
    104        select_candidates = exp.Window if expression.is_star else (exp.Window, exp.Column)
    105        for expr in qualify_filters.find_all(select_candidates):
    106            if isinstance(expr, exp.Window):
    107                alias = find_new_name(expression.named_selects, "_w")
    108                expression.select(exp.alias_(expr, alias), copy=False)
    109                column = exp.column(alias)
    110
    111                if isinstance(expr.parent, exp.Qualify):
    112                    qualify_filters = column
    113                else:
    114                    expr.replace(column)
    115            elif expr.name not in expression.named_selects:
    116                expression.select(expr.copy(), copy=False)
    117
    118        return outer_selects.from_(expression.subquery(alias="_t")).where(qualify_filters)
    119
    120    return expression

Convert SELECT statements that contain the QUALIFY clause into subqueries, filtered equivalently.

The idea behind this transformation can be seen in Snowflake's documentation for QUALIFY: https://docs.snowflake.com/en/sql-reference/constructs/qualify

Some dialects don't support window functions in the WHERE clause, so we need to include them as projections in the subquery, in order to refer to them in the outer filter using aliases. Also, if a column is referenced in the QUALIFY clause but is not selected, we need to include it too, otherwise we won't be able to refer to it in the outer query's WHERE clause.

def remove_precision_parameterized_types( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

    123def remove_precision_parameterized_types(expression: exp.Expression) -> exp.Expression:
    124    """
    125    Some dialects only allow the precision for parameterized types to be defined in the DDL and not in
    126    other expressions. This transforms removes the precision from parameterized types in expressions.
    127    """
    128    for node in expression.find_all(exp.DataType):
    129        node.set(
    130            "expressions", [e for e in node.expressions if not isinstance(e, exp.DataTypeSize)]
    131        )
    132
    133    return expression

Some dialects only allow the precision for parameterized types to be defined in the DDL and not in other expressions. This transforms removes the precision from parameterized types in expressions.

def unnest_to_explode( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

    136def unnest_to_explode(expression: exp.Expression) -> exp.Expression:
    137    """Convert cross join unnest into lateral view explode (used in presto -> hive)."""
    138    if isinstance(expression, exp.Select):
    139        for join in expression.args.get("joins") or []:
    140            unnest = join.this
    141
    142            if isinstance(unnest, exp.Unnest):
    143                alias = unnest.args.get("alias")
    144                udtf = exp.Posexplode if unnest.args.get("ordinality") else exp.Explode
    145
    146                expression.args["joins"].remove(join)
    147
    148                for e, column in zip(unnest.expressions, alias.columns if alias else []):
    149                    expression.append(
    150                        "laterals",
    151                        exp.Lateral(
    152                            this=udtf(this=e),
    153                            view=True,
    154                            alias=exp.TableAlias(this=alias.this, columns=[column]),  # type: ignore
    155                        ),
    156                    )
    157
    158    return expression

Convert cross join unnest into lateral view explode (used in presto -> hive).

def explode_to_unnest( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

    161def explode_to_unnest(expression: exp.Expression) -> exp.Expression:
    162    """Convert explode/posexplode into unnest (used in hive -> presto)."""
    163    if isinstance(expression, exp.Select):
    164        from sqlglot.optimizer.scope import Scope
    165
    166        taken_select_names = set(expression.named_selects)
    167        taken_source_names = {name for name, _ in Scope(expression).references}
    168
    169        for select in expression.selects:
    170            to_replace = select
    171
    172            pos_alias = ""
    173            explode_alias = ""
    174
    175            if isinstance(select, exp.Alias):
    176                explode_alias = select.alias
    177                select = select.this
    178            elif isinstance(select, exp.Aliases):
    179                pos_alias = select.aliases[0].name
    180                explode_alias = select.aliases[1].name
    181                select = select.this
    182
    183            if isinstance(select, (exp.Explode, exp.Posexplode)):
    184                is_posexplode = isinstance(select, exp.Posexplode)
    185
    186                explode_arg = select.this
    187                unnest = exp.Unnest(expressions=[explode_arg.copy()], ordinality=is_posexplode)
    188
    189                # This ensures that we won't use [POS]EXPLODE's argument as a new selection
    190                if isinstance(explode_arg, exp.Column):
    191                    taken_select_names.add(explode_arg.output_name)
    192
    193                unnest_source_alias = find_new_name(taken_source_names, "_u")
    194                taken_source_names.add(unnest_source_alias)
    195
    196                if not explode_alias:
    197                    explode_alias = find_new_name(taken_select_names, "col")
    198                    taken_select_names.add(explode_alias)
    199
    200                    if is_posexplode:
    201                        pos_alias = find_new_name(taken_select_names, "pos")
    202                        taken_select_names.add(pos_alias)
    203
    204                if is_posexplode:
    205                    column_names = [explode_alias, pos_alias]
    206                    to_replace.pop()
    207                    expression.select(pos_alias, explode_alias, copy=False)
    208                else:
    209                    column_names = [explode_alias]
    210                    to_replace.replace(exp.column(explode_alias))
    211
    212                unnest = exp.alias_(unnest, unnest_source_alias, table=column_names)
    213
    214                if not expression.args.get("from"):
    215                    expression.from_(unnest, copy=False)
    216                else:
    217                    expression.join(unnest, join_type="CROSS", copy=False)
    218
    219    return expression

Convert explode/posexplode into unnest (used in hive -> presto).

def remove_within_group_for_percentiles( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

    222def remove_within_group_for_percentiles(expression: exp.Expression) -> exp.Expression:
    223    if (
    224        isinstance(expression, exp.WithinGroup)
    225        and isinstance(expression.this, (exp.PercentileCont, exp.PercentileDisc))
    226        and isinstance(expression.expression, exp.Order)
    227    ):
    228        quantile = expression.this.this
    229        input_value = t.cast(exp.Ordered, expression.find(exp.Ordered)).this
    230        return expression.replace(exp.ApproxQuantile(this=input_value, quantile=quantile))
    231
    232    return expression

def add_recursive_cte_column_names( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

    235def add_recursive_cte_column_names(expression: exp.Expression) -> exp.Expression:
    236    if isinstance(expression, exp.With) and expression.recursive:
    237        next_name = name_sequence("_c_")
    238
    239        for cte in expression.expressions:
    240            if not cte.args["alias"].columns:
    241                query = cte.this
    242                if isinstance(query, exp.Union):
    243                    query = query.this
    244
    245                cte.args["alias"].set(
    246                    "columns",
    247                    [exp.to_identifier(s.alias_or_name or next_name()) for s in query.selects],
    248                )
    249
    250    return expression

def epoch_cast_to_ts( expression: sqlglot.expressions.Expression) -> sqlglot.expressions.Expression: View Source

    253def epoch_cast_to_ts(expression: exp.Expression) -> exp.Expression:
    254    if (
    255        isinstance(expression, (exp.Cast, exp.TryCast))
    256        and expression.name.lower() == "epoch"
    257        and expression.to.this in exp.DataType.TEMPORAL_TYPES
    258    ):
    259        expression.this.replace(exp.Literal.string("1970-01-01 00:00:00"))
    260
    261    return expression

def preprocess( transforms: List[Callable[[sqlglot.expressions.Expression], sqlglot.expressions.Expression]]) -> Callable[[sqlglot.generator.Generator, sqlglot.expressions.Expression], str]: View Source

    264def preprocess(
    265    transforms: t.List[t.Callable[[exp.Expression], exp.Expression]],
    266) -> t.Callable[[Generator, exp.Expression], str]:
    267    """
    268    Creates a new transform by chaining a sequence of transformations and converts the resulting
    269    expression to SQL, using either the "_sql" method corresponding to the resulting expression,
    270    or the appropriate `Generator.TRANSFORMS` function (when applicable -- see below).
    271
    272    Args:
    273        transforms: sequence of transform functions. These will be called in order.
    274
    275    Returns:
    276        Function that can be used as a generator transform.
    277    """
    278
    279    def _to_sql(self, expression: exp.Expression) -> str:
    280        expression_type = type(expression)
    281
    282        expression = transforms[0](expression.copy())
    283        for t in transforms[1:]:
    284            expression = t(expression)
    285
    286        _sql_handler = getattr(self, expression.key + "_sql", None)
    287        if _sql_handler:
    288            return _sql_handler(expression)
    289
    290        transforms_handler = self.TRANSFORMS.get(type(expression))
    291        if transforms_handler:
    292            # Ensures we don't enter an infinite loop. This can happen when the original expression
    293            # has the same type as the final expression and there's no _sql method available for it,
    294            # because then it'd re-enter _to_sql.
    295            if expression_type is type(expression):
    296                raise ValueError(
    297                    f"Expression type {expression.__class__.__name__} requires a _sql method in order to be transformed."
    298                )
    299
    300            return transforms_handler(self, expression)
    301
    302        raise ValueError(f"Unsupported expression type {expression.__class__.__name__}.")
    303
    304    return _to_sql

Creates a new transform by chaining a sequence of transformations and converts the resulting expression to SQL, using either the "_sql" method corresponding to the resulting expression, or the appropriate `Generator.TRANSFORMS` function (when applicable -- see below).

###### Arguments:

- transforms: sequence of transform functions. These will be called in order.

###### Returns:

> Function that can be used as a generator transform.