feat(api): add TableUnnest operation to support cross-join unnest semantics as well as offset

ibis/backends/bigquery/compiler.py

@@ -690,3 +690,47 @@
         table = sg.to_identifier(parent.alias_or_name, quoted=quoted)
         column = sge.Column(this=star, table=table)
         return sg.select(column).from_(parent)
+
+    def visit_TableUnnest(
+        self, op, *, parent, column, offset: str | None, keep_empty: bool
+    ):
+        quoted = self.quoted
+
+        column_alias = sg.to_identifier(
+            util.gen_name("table_unnest_column"), quoted=quoted
+        )
+
+        selcols = []
+
+        table = sg.to_identifier(parent.alias_or_name, quoted=quoted)
+
+        opname = op.column.name
+        overlaps_with_parent = opname in op.parent.schema
+        computed_column = column_alias.as_(opname, quoted=quoted)
+
+        # replace the existing column if the unnested column hasn't been
+        # renamed
+        #
+        # e.g., table.unnest("x")
+        if overlaps_with_parent:
+            selcols.append(
+                sge.Column(this=sge.Star(replace=[computed_column]), table=table)
+            )
+        else:
+            selcols.append(sge.Column(this=STAR, table=table))
+            selcols.append(computed_column)
+
+        if offset is not None:
+            offset = sg.to_identifier(offset, quoted=quoted)
+            selcols.append(offset)
+
+        unnest = sge.Unnest(
+            expressions=[column],
+            alias=sge.TableAlias(columns=[column_alias]),
+            offset=offset,
+        )
+        return (
+            sg.select(*selcols)
+            .from_(parent)
+            .join(unnest, join_type="CROSS" if not keep_empty else "LEFT")
+        )

ibis/backends/clickhouse/compiler.py

@@ -648,3 +648,60 @@
         table = sg.to_identifier(parent.alias_or_name, quoted=quoted)
         column = sge.Column(this=star, table=table)
         return sg.select(column).from_(parent)
+
+    def visit_TableUnnest(
+        self, op, *, parent, column, offset: str | None, keep_empty: bool
+    ):
+        quoted = self.quoted
+
+        column_alias = sg.to_identifier(
+            util.gen_name("table_unnest_column"), quoted=quoted
+        )
+
+        table = sg.to_identifier(parent.alias_or_name, quoted=quoted)
+
+        selcols = []
+
+        opname = op.column.name
+        overlaps_with_parent = opname in op.parent.schema
+        computed_column = column_alias.as_(opname, quoted=quoted)
+
+        if offset is not None:
+            if overlaps_with_parent:
+                selcols.append(
+                    sge.Column(this=sge.Star(replace=[computed_column]), table=table)
+                )
+            else:
+                selcols.append(sge.Column(this=STAR, table=table))
+                selcols.append(computed_column)
+
+            offset = sg.to_identifier(offset, quoted=quoted)
+            selcols.append(offset)
+        elif overlaps_with_parent:
+            selcols.append(
+                sge.Column(this=sge.Star(replace=[computed_column]), table=table)
+            )
+        else:
+            selcols.append(sge.Column(this=STAR, table=table))
+            selcols.append(computed_column)
+
+        select = (
+            sg.select(*selcols)
+            .from_(parent)
+            .join(
+                sge.Join(
+                    this=column.as_(column_alias, quoted=quoted),
+                    kind="ARRAY",
+                    side=None if not keep_empty else "LEFT",
+                )
+            )
+        )
+
+        if offset is not None:
+            param = sg.to_identifier(util.gen_name("arr_enum"))
+            func = sge.Lambda(this=param - 1, expressions=[param])
+            return select.join(
+                self.f.arrayMap(func, self.f.arrayEnumerate(column_alias)).as_(offset)
+            )
+
+        return select

ibis/backends/duckdb/compiler.py

@@ -14,6 +14,7 @@
 from ibis.backends.sql.compiler import NULL, STAR, AggGen, SQLGlotCompiler
 from ibis.backends.sql.datatypes import DuckDBType
 from ibis.backends.sql.rewrites import exclude_nulls_from_array_collect
+from ibis.util import gen_name
 
 _INTERVAL_SUFFIXES = {
     "ms": "milliseconds",
@@ -547,3 +548,55 @@
         table = sg.to_identifier(parent.alias_or_name, quoted=quoted)
         column = sge.Column(this=star, table=table)
         return sg.select(column).from_(parent)
+
+    def visit_TableUnnest(
+        self, op, *, parent, column, offset: str | None, keep_empty: bool
+    ):
+        quoted = self.quoted
+
+        column_alias = sg.to_identifier(gen_name("table_unnest_column"), quoted=quoted)
+
+        opname = op.column.name
+        overlaps_with_parent = opname in op.parent.schema
+        computed_column = column_alias.as_(opname, quoted=quoted)
+
+        selcols = []
+
+        table = sg.to_identifier(parent.alias_or_name, quoted=quoted)
+
+        if offset is not None:
+            # TODO: clean this up once WITH ORDINALITY is supported in DuckDB
+            # no need for struct_extract once that's upstream
+            column = self.f.list_zip(column, self.f.range(self.f.len(column)))
+            extract = self.f.struct_extract(column_alias, 1).as_(opname, quoted=quoted)
+
+            if overlaps_with_parent:
+                replace = sge.Column(this=sge.Star(replace=[extract]), table=table)
+                selcols.append(replace)
+            else:
+                selcols.append(sge.Column(this=STAR, table=table))
+                selcols.append(extract)
+
+            selcols.append(
+                self.f.struct_extract(column_alias, 2).as_(offset, quoted=quoted)
+            )
+        elif overlaps_with_parent:
+            selcols.append(
+                sge.Column(this=sge.Star(replace=[computed_column]), table=table)
+            )
+        else:
+            selcols.append(sge.Column(this=STAR, table=table))
+            selcols.append(computed_column)
+
+        unnest = sge.Unnest(
+            expressions=[column],
+            alias=sge.TableAlias(
+                this=sg.to_identifier(gen_name("table_unnest"), quoted=quoted),
+                columns=[column_alias],
+            ),
+        )
+        return (
+            sg.select(*selcols)
+            .from_(parent)
+            .join(unnest, join_type="CROSS" if not keep_empty else "LEFT")
+        )

ibis/backends/postgres/compiler.py

@@ -15,6 +15,7 @@
 from ibis.backends.sql.datatypes import PostgresType
 from ibis.backends.sql.dialects import Postgres
 from ibis.backends.sql.rewrites import exclude_nulls_from_array_collect
+from ibis.util import gen_name
 
 
 class PostgresUDFNode(ops.Value):
@@ -611,3 +612,59 @@ def visit_Hash(self, op, *, arg):
             f"Hash({arg_dtype!r}) operation is not supported in the "
             f"{self.dialect} backend"
         )
+
+    def visit_TableUnnest(
+        self, op, *, parent, column, offset: str | None, keep_empty: bool
+    ):
+        quoted = self.quoted
+
+        column_alias = sg.to_identifier(gen_name("table_unnest_column"), quoted=quoted)
+
+        parent_alias = parent.alias_or_name
+
+        opname = op.column.name
+        parent_schema = op.parent.schema
+        overlaps_with_parent = opname in parent_schema
+        computed_column = column_alias.as_(opname, quoted=quoted)
+
+        selcols = []
+
+        if overlaps_with_parent:
+            column_alias_or_name = column.alias_or_name
+            selcols.extend(
+                sg.column(col, table=parent_alias, quoted=quoted)
+                if col != column_alias_or_name
+                else computed_column
+                for col in parent_schema.names
+            )
+        else:
+            selcols.append(
+                sge.Column(
+                    this=STAR, table=sg.to_identifier(parent_alias, quoted=quoted)
+                )
+            )
+            selcols.append(computed_column)
+
+        if offset is not None:
+            offset_name = offset
+            offset = sg.to_identifier(offset_name, quoted=quoted)
+            selcols.append((offset - 1).as_(offset_name, quoted=quoted))
+
+        unnest = sge.Unnest(
+            expressions=[column],
+            alias=sge.TableAlias(
+                this=sg.to_identifier(gen_name("table_unnest"), quoted=quoted),
+                columns=[column_alias],
+            ),
+            offset=offset,
+        )
+
+        return (
+            sg.select(*selcols)
+            .from_(parent)
+            .join(
+                unnest,
+                on=None if not keep_empty else sge.convert(True),
+                join_type="CROSS" if not keep_empty else "LEFT",
+            )
+        )

ibis/backends/pyspark/compiler.py

@@ -452,3 +452,68 @@
             return self.f.sha2(arg, int(how[-3:]))
         else:
             raise NotImplementedError(f"No available hashing function for {how}")
+
+    def visit_TableUnnest(
+        self, op, *, parent, column, offset: str | None, keep_empty: bool
+    ):
+        quoted = self.quoted
+
+        column_alias = sg.to_identifier(gen_name("table_unnest_column"), quoted=quoted)
+
+        opname = op.column.name
+        parent_schema = op.parent.schema
+        overlaps_with_parent = opname in parent_schema
+        computed_column = column_alias.as_(opname, quoted=quoted)
+
+        parent_alias = parent.alias_or_name
+
+        selcols = []
+
+        if overlaps_with_parent:
+            column_alias_or_name = column.alias_or_name
+            selcols.extend(
+                sg.column(col, table=parent_alias, quoted=quoted)
+                if col != column_alias_or_name
+                else computed_column
+                for col in parent_schema.names
+            )
+        else:
+            selcols.append(
+                sge.Column(
+                    this=STAR, table=sg.to_identifier(parent_alias, quoted=quoted)
+                )
+            )
+            selcols.append(computed_column)
+
+        alias_columns = []
+
+        if offset is not None:
+            offset = sg.column(offset, quoted=quoted)
+            selcols.append(offset)
+            alias_columns.append(offset)
+
+        alias_columns.append(column_alias)
+
+        # four possible functions
+        #
+        # explode: unnest
+        # explode_outer: unnest preserving empties and nulls
+        # posexplode: unnest with index
+        # posexplode_outer: unnest with index preserving empties and nulls
+        funcname = (
+            ("pos" if offset is not None else "")
+            + "explode"
+            + ("_outer" if keep_empty else "")
+        )
+
+        return (
+            sg.select(*selcols)
+            .from_(parent)
+            .lateral(
+                sge.Lateral(
+                    this=self.f[funcname](column),
+                    view=True,
+                    alias=sge.TableAlias(columns=alias_columns),
+                )
+            )
+        )

ibis/backends/snowflake/compiler.py

@@ -662,3 +662,70 @@
         table = sg.to_identifier(parent.alias_or_name, quoted=quoted)
         column = sge.Column(this=star, table=table)
         return sg.select(column).from_(parent)
+
+    def visit_TableUnnest(
+        self, op, *, parent, column, offset: str | None, keep_empty: bool
+    ):
+        quoted = self.quoted
+
+        column_alias = sg.to_identifier(
+            util.gen_name("table_unnest_column"), quoted=quoted
+        )
+
+        sep = sge.convert(util.guid())
+        null_sentinel = sge.convert(util.guid())
+
+        table = sg.to_identifier(parent.alias_or_name, quoted=quoted)
+
+        selcols = []
+
+        opcol = op.column
+        opname = opcol.name
+        overlaps_with_parent = opname in op.parent.schema
+        computed_column = self.cast(
+            self.f.nullif(column_alias, null_sentinel), opcol.dtype.value_type
+        ).as_(opname, quoted=quoted)
+
+        if overlaps_with_parent:
+            selcols.append(
+                sge.Column(this=sge.Star(replace=[computed_column]), table=table)
+            )
+        else:
+            selcols.append(sge.Column(this=STAR, table=table))
+            selcols.append(computed_column)
+
+        if offset is not None:
+            offset = sg.to_identifier(offset, quoted=quoted)
+            selcols.append(offset)
+
+        alias = sge.TableAlias(
+            this=sg.to_identifier(util.gen_name("table_unnest"), quoted=quoted),
+            columns=[column_alias],
+        )
+
+        # there has to be a better way
+        param = sg.to_identifier(util.gen_name("table_unnest_param"))
+        column = self.f.transform(
+            column,
+            sge.Lambda(
+                this=self.f.coalesce(self.cast(param, dt.string), null_sentinel),
+                expressions=[param],
+            ),
+        )
+        empty_array = self.f.array()
+        split = self.f.coalesce(
+            self.f.nullif(
+                self.f.split(
+                    self.f.array_to_string(self.f.nullif(column, empty_array), sep), sep
+                ),
+                empty_array,
+            ),
+            self.f.array(null_sentinel),
+        )
+
+        unnest = sge.Unnest(expressions=[split], alias=alias, offset=offset)
+        return (
+            sg.select(*selcols)
+            .from_(parent)
+            .join(unnest, join_type="CROSS" if not keep_empty else "LEFT")
+        )