Add support of MATERIAILZED/ALIAS/EPHERMERAL default column options for ClickHouse

ClickHouse supports using MATERIAILZED/ALIAS/EPHERMERAL expression to
set the default value while creating table.

For detailed syntax, please refer to: https://clickhouse.com/docs/en/sql-reference/statements/create/table#default_values

Author: git-hulk

src/ast/ddl.rs

@@ -923,6 +923,18 @@ pub enum ColumnOption {
     NotNull,
     /// `DEFAULT <restricted-expr>`
     Default(Expr),
+
+    /// ClickHouse supports `MATERIALIZE`, `EPHEMERAL` and `ALIAS` expr to generate default values.
+    /// Syntax: `b INT MATERIALIZE (a + 1)`
+    /// [ClickHouse](https://clickhouse.com/docs/en/sql-reference/statements/create/table#default_values)
+
+    /// MATERIALIZE <expr>
+    Materialized(Expr),
+    /// EPHEMERAL [<expr>]
+    Ephemeral(Option<Expr>),
+    /// ALIAS <expr>
+    Alias(Expr),
+
     /// `{ PRIMARY KEY | UNIQUE } [<constraint_characteristics>]`
     Unique {
         is_primary: bool,
@@ -978,6 +990,15 @@ impl fmt::Display for ColumnOption {
             Null => write!(f, "NULL"),
             NotNull => write!(f, "NOT NULL"),
             Default(expr) => write!(f, "DEFAULT {expr}"),
+            Materialized(expr) => write!(f, "MATERIALIZED {expr}"),
+            Ephemeral(expr) => {
+                if let Some(e) = expr {
+                    write!(f, "EPHEMERAL {e}")
+                } else {
+                    write!(f, "EPHEMERAL")
+                }
+            }
+            Alias(expr) => write!(f, "ALIAS {expr}"),
             Unique {
                 is_primary,
                 characteristics,

src/keywords.rs

@@ -77,6 +77,7 @@ define_keywords!(
     AFTER,
     AGAINST,
     AGGREGATION,
+    ALIAS,
     ALL,
     ALLOCATE,
     ALTER,
@@ -267,6 +268,7 @@ define_keywords!(
     ENFORCED,
     ENGINE,
     ENUM,
+    EPHEMERAL,
     EPOCH,
     EQUALS,
     ERROR,

src/parser/mod.rs

@@ -5743,6 +5743,24 @@ impl<'a> Parser<'a> {
             Ok(Some(ColumnOption::Null))
         } else if self.parse_keyword(Keyword::DEFAULT) {
             Ok(Some(ColumnOption::Default(self.parse_expr()?)))
+        } else if dialect_of!(self is ClickHouseDialect| GenericDialect)
+            && self.parse_keyword(Keyword::MATERIALIZED)
+        {
+            Ok(Some(ColumnOption::Materialized(self.parse_expr()?)))
+        } else if dialect_of!(self is ClickHouseDialect| GenericDialect)
+            && self.parse_keyword(Keyword::ALIAS)
+        {
+            Ok(Some(ColumnOption::Alias(self.parse_expr()?)))
+        } else if dialect_of!(self is ClickHouseDialect| GenericDialect)
+            && self.parse_keyword(Keyword::EPHEMERAL)
+        {
+            // The expression is optional for the EPHEMERAL syntax, so we need to check
+            // if the column definition has remaining tokens before parsing the expression.
+            if matches!(self.peek_token().token, Token::Comma | Token::RParen) {
+                Ok(Some(ColumnOption::Ephemeral(None)))
+            } else {
+                Ok(Some(ColumnOption::Ephemeral(Some(self.parse_expr()?))))
+            }
         } else if self.parse_keywords(&[Keyword::PRIMARY, Keyword::KEY]) {
             let characteristics = self.parse_constraint_characteristics()?;
             Ok(Some(ColumnOption::Unique {

tests/sqlparser_clickhouse.rs

@@ -493,6 +493,102 @@ fn parse_create_table_with_primary_key() {
         .expect_err("ORDER BY supports one expression with tuple");
 }
 
+#[test]
+fn parse_create_table_with_variant_default_expressions() {
+    let sql = concat!(
+        "CREATE TABLE table (",
+        "a DATETIME MATERIALIZED now(),",
+        " b DATETIME EPHEMERAL now(),",
+        " c DATETIME EPHEMERAL,",
+        " d STRING ALIAS toString(c)",
+        ") ENGINE=MergeTree"
+    );
+    match clickhouse_and_generic().verified_stmt(sql) {
+        Statement::CreateTable(CreateTable { columns, .. }) => {
+            assert_eq!(
+                columns,
+                vec![
+                    ColumnDef {
+                        name: Ident::new("a"),
+                        data_type: DataType::Datetime(None),
+                        collation: None,
+                        options: vec![ColumnOptionDef {
+                            name: None,
+                            option: ColumnOption::Materialized(Expr::Function(Function {
+                                name: ObjectName(vec![Ident::new("now")]),
+                                args: FunctionArguments::List(FunctionArgumentList {
+                                    args: vec![],
+                                    duplicate_treatment: None,
+                                    clauses: vec![],
+                                }),
+                                parameters: FunctionArguments::None,
+                                null_treatment: None,
+                                filter: None,
+                                over: None,
+                                within_group: vec![],
+                            }))
+                        }],
+                    },
+                    ColumnDef {
+                        name: Ident::new("b"),
+                        data_type: DataType::Datetime(None),
+                        collation: None,
+                        options: vec![ColumnOptionDef {
+                            name: None,
+                            option: ColumnOption::Ephemeral(Some(Expr::Function(Function {
+                                name: ObjectName(vec![Ident::new("now")]),
+                                args: FunctionArguments::List(FunctionArgumentList {
+                                    args: vec![],
+                                    duplicate_treatment: None,
+                                    clauses: vec![],
+                                }),
+                                parameters: FunctionArguments::None,
+                                null_treatment: None,
+                                filter: None,
+                                over: None,
+                                within_group: vec![],
+                            })))
+                        }],
+                    },
+                    ColumnDef {
+                        name: Ident::new("c"),
+                        data_type: DataType::Datetime(None),
+                        collation: None,
+                        options: vec![ColumnOptionDef {
+                            name: None,
+                            option: ColumnOption::Ephemeral(None)
+                        }],
+                    },
+                    ColumnDef {
+                        name: Ident::new("d"),
+                        data_type: DataType::String(None),
+                        collation: None,
+                        options: vec![ColumnOptionDef {
+                            name: None,
+                            option: ColumnOption::Alias(Expr::Function(Function {
+                                name: ObjectName(vec![Ident::new("toString")]),
+                                args: FunctionArguments::List(FunctionArgumentList {
+                                    args: vec![FunctionArg::Unnamed(FunctionArgExpr::Expr(
+                                        Identifier(Ident::new("c"))
+                                    ))],
+                                    duplicate_treatment: None,
+                                    clauses: vec![],
+                                }),
+                                parameters: FunctionArguments::None,
+                                null_treatment: None,
+                                filter: None,
+                                over: None,
+                                within_group: vec![],
+                            }))
+                        }],
+                    }
+                ]
+            )
+        }
+        _ => unreachable!(),
+    }
+}
+
 #[test]
 fn parse_create_view_with_fields_data_types() {
     match clickhouse().verified_stmt(r#"CREATE VIEW v (i "int", f "String") AS SELECT * FROM t"#) {