Support for DuckDB Union datatype

src/ast/data_type.rs

@@ -20,7 +20,7 @@ use serde::{Deserialize, Serialize};
 #[cfg(feature = "visitor")]
 use sqlparser_derive::{Visit, VisitMut};
 
-use crate::ast::{display_comma_separated, ObjectName, StructField};
+use crate::ast::{display_comma_separated, ObjectName, StructField, UnionField};
 
 use super::{value::escape_single_quote_string, ColumnDef};
 
@@ -303,6 +303,10 @@ pub enum DataType {
     /// [hive]: https://docs.cloudera.com/cdw-runtime/cloud/impala-sql-reference/topics/impala-struct.html
     /// [bigquery]: https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types#struct_type
     Struct(Vec<StructField>),
+    /// Union
+    ///
+    /// [duckdb]: https://duckdb.org/docs/sql/data_types/union.html
+    Union(Vec<UnionField>),
     /// Nullable - special marker NULL represents in ClickHouse as a data type.
     ///
     /// [clickhouse]: https://clickhouse.com/docs/en/sql-reference/data-types/nullable
@@ -516,6 +520,9 @@ impl fmt::Display for DataType {
                     write!(f, "STRUCT")
                 }
             }
+            DataType::Union(fields) => {
+                write!(f, "UNION({})", display_comma_separated(fields))
+            }
             // ClickHouse
             DataType::Nullable(data_type) => {
                 write!(f, "Nullable({})", data_type)

src/ast/mod.rs

@@ -294,6 +294,23 @@ impl fmt::Display for StructField {
     }
 }
 
+/// A field definition within a union
+///
+/// [duckdb]: https://duckdb.org/docs/sql/data_types/union.html
+#[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
+pub struct UnionField {
+    pub field_name: Ident,
+    pub field_type: DataType,
+}
+
+impl fmt::Display for UnionField {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} {}", self.field_name, self.field_type)
+    }
+}
+
 /// A dictionary field within a dictionary.
 ///
 /// [duckdb]: https://duckdb.org/docs/sql/data_types/struct#creating-structs

src/parser/mod.rs

@@ -2246,6 +2246,32 @@ impl<'a> Parser<'a> {
         ))
     }
 
+    /// DuckDB specific: Parse a Union type definition as a sequence of field-value pairs.
+    ///
+    /// Syntax:
+    ///
+    /// ```sql
+    /// UNION(field_name field_type[,...])
+    /// ```
+    ///
+    /// [1]: https://duckdb.org/docs/sql/data_types/union.html
+    fn parse_union_type_def(&mut self) -> Result<Vec<UnionField>, ParserError> {
+        self.expect_keyword(Keyword::UNION)?;
+
+        self.expect_token(&Token::LParen)?;
+
+        let fields = self.parse_comma_separated(|p| {
+            Ok(UnionField {
+                field_name: p.parse_identifier(false)?,
+                field_type: p.parse_data_type()?,
+            })
+        })?;
+
+        self.expect_token(&Token::RParen)?;
+
+        Ok(fields)
+    }
+
     /// DuckDB specific: Parse a duckdb dictionary [1]
     ///
     /// Syntax:
@@ -7136,6 +7162,11 @@ impl<'a> Parser<'a> {
                     trailing_bracket = _trailing_bracket;
                     Ok(DataType::Struct(field_defs))
                 }
+                Keyword::UNION if dialect_of!(self is DuckDbDialect | GenericDialect) => {
+                    self.prev_token();
+                    let fields = self.parse_union_type_def()?;
+                    Ok(DataType::Union(fields))
+                }
                 Keyword::NULLABLE if dialect_of!(self is ClickHouseDialect | GenericDialect) => {
                     Ok(self.parse_sub_type(DataType::Nullable)?)
                 }

tests/sqlparser_duckdb.rs

@@ -545,3 +545,98 @@ fn test_array_index() {
         expr
     );
 }
+
+#[test]
+fn test_duckdb_union_datatype() {
+    let sql = "CREATE TABLE tbl1 (one UNION(a INT), two UNION(a INT, b INT), nested UNION(a UNION(b INT)))";
+    let stmt = duckdb_and_generic().verified_stmt(sql);
+    assert_eq!(
+        Statement::CreateTable(CreateTable {
+            or_replace: Default::default(),
+            temporary: Default::default(),
+            external: Default::default(),
+            global: Default::default(),
+            if_not_exists: Default::default(),
+            transient: Default::default(),
+            volatile: Default::default(),
+            name: ObjectName(vec!["tbl1".into()]),
+            columns: vec![
+                ColumnDef {
+                    name: "one".into(),
+                    data_type: DataType::Union(vec![UnionField {
+                        field_name: "a".into(),
+                        field_type: DataType::Int(None)
+                    }]),
+                    collation: Default::default(),
+                    options: Default::default()
+                },
+                ColumnDef {
+                    name: "two".into(),
+                    data_type: DataType::Union(vec![
+                        UnionField {
+                            field_name: "a".into(),
+                            field_type: DataType::Int(None)
+                        },
+                        UnionField {
+                            field_name: "b".into(),
+                            field_type: DataType::Int(None)
+                        }
+                    ]),
+                    collation: Default::default(),
+                    options: Default::default()
+                },
+                ColumnDef {
+                    name: "nested".into(),
+                    data_type: DataType::Union(vec![UnionField {
+                        field_name: "a".into(),
+                        field_type: DataType::Union(vec![UnionField {
+                            field_name: "b".into(),
+                            field_type: DataType::Int(None)
+                        }])
+                    }]),
+                    collation: Default::default(),
+                    options: Default::default()
+                }
+            ],
+            constraints: Default::default(),
+            hive_distribution: HiveDistributionStyle::NONE,
+            hive_formats: Some(HiveFormat {
+                row_format: Default::default(),
+                serde_properties: Default::default(),
+                storage: Default::default(),
+                location: Default::default()
+            }),
+            table_properties: Default::default(),
+            with_options: Default::default(),
+            file_format: Default::default(),
+            location: Default::default(),
+            query: Default::default(),
+            without_rowid: Default::default(),
+            like: Default::default(),
+            clone: Default::default(),
+            engine: Default::default(),
+            comment: Default::default(),
+            auto_increment_offset: Default::default(),
+            default_charset: Default::default(),
+            collation: Default::default(),
+            on_commit: Default::default(),
+            on_cluster: Default::default(),
+            primary_key: Default::default(),
+            order_by: Default::default(),
+            partition_by: Default::default(),
+            cluster_by: Default::default(),
+            options: Default::default(),
+            strict: Default::default(),
+            copy_grants: Default::default(),
+            enable_schema_evolution: Default::default(),
+            change_tracking: Default::default(),
+            data_retention_time_in_days: Default::default(),
+            max_data_extension_time_in_days: Default::default(),
+            default_ddl_collation: Default::default(),
+            with_aggregation_policy: Default::default(),
+            with_row_access_policy: Default::default(),
+            with_tags: Default::default()
+        }),
+        stmt
+    );
+}