From aa8fc0d45d8e7826625913f45d9c9dc64dcfd234 Mon Sep 17 00:00:00 2001
From: Egor Vorontsov <sdoregor@sdore.me>
Date: Sat, 8 Nov 2025 02:08:56 +0300
Subject: [PATCH] Implemented NULL literal in SQL for Units and Options.

---
 crates/expr/src/expr.rs             | 17 +++++++++++++++++
 crates/expr/src/lib.rs              |  4 ++++
 crates/expr/src/statement.rs        | 19 +++++++++++++++++++
 crates/sql-parser/src/ast/mod.rs    |  2 ++
 crates/sql-parser/src/parser/mod.rs |  1 +
 5 files changed, 43 insertions(+)

diff --git a/crates/expr/src/expr.rs b/crates/expr/src/expr.rs
index 92883df0cc9..5c9c262ef3b 100644
--- a/crates/expr/src/expr.rs
+++ b/crates/expr/src/expr.rs
@@ -351,6 +351,23 @@ impl Expr {
         }
     }
 
+    /// A literal unit value
+    pub fn unit() -> Self {
+        Self::Value(AlgebraicValue::unit(), AlgebraicType::unit())
+    }
+
+    /// A literal option none value
+    #[allow(non_snake_case)]
+    pub fn OptionNone(ty: AlgebraicType) -> Self {
+        Self::Value(AlgebraicValue::OptionNone(), AlgebraicType::option(ty))
+    }
+
+    /// A literal option none value
+    #[allow(non_snake_case)]
+    pub fn OptionSome(ty: AlgebraicType, v: AlgebraicValue) -> Self {
+        Self::Value(AlgebraicValue::OptionSome(v), AlgebraicType::option(ty))
+    }
+
     /// A literal boolean value
     pub const fn bool(v: bool) -> Self {
         Self::Value(AlgebraicValue::Bool(v), AlgebraicType::Bool)
diff --git a/crates/expr/src/lib.rs b/crates/expr/src/lib.rs
index 2d9b3cdc5ab..94b28fb6b5c 100644
--- a/crates/expr/src/lib.rs
+++ b/crates/expr/src/lib.rs
@@ -88,6 +88,10 @@ fn _type_expr(vars: &Relvars, expr: SqlExpr, expected: Option<&AlgebraicType>, d
     recursion::guard(depth, recursion::MAX_RECURSION_TYP_EXPR, "expr::type_expr")?;
 
     match (expr, expected) {
+        (SqlExpr::Lit(SqlLiteral::Null), None) => Ok(Expr::unit()),
+        (SqlExpr::Lit(SqlLiteral::Null), Some(ty)) if ty.is_unit() => Ok(Expr::unit()),
+        (SqlExpr::Lit(SqlLiteral::Null), Some(ty)) if ty.is_option() => Ok(Expr::OptionNone(ty.clone())),
+        (SqlExpr::Lit(SqlLiteral::Null), Some(ty)) => Err(UnexpectedType::new(&AlgebraicType::unit(), ty).into()),
         (SqlExpr::Lit(SqlLiteral::Bool(v)), None | Some(AlgebraicType::Bool)) => Ok(Expr::bool(v)),
         (SqlExpr::Lit(SqlLiteral::Bool(_)), Some(ty)) => Err(UnexpectedType::new(&AlgebraicType::Bool, ty).into()),
         (SqlExpr::Lit(SqlLiteral::Str(_) | SqlLiteral::Num(_) | SqlLiteral::Hex(_)), None) => {
diff --git a/crates/expr/src/statement.rs b/crates/expr/src/statement.rs
index 8a3aa3a8d70..378ca3de968 100644
--- a/crates/expr/src/statement.rs
+++ b/crates/expr/src/statement.rs
@@ -137,6 +137,15 @@ pub fn type_insert(insert: SqlInsert, tx: &impl SchemaView) -> TypingResult<Tabl
                 .map(|ColumnSchema { col_type, .. }| col_type),
         ) {
             match (value, ty) {
+                (SqlLiteral::Null, _) if ty.is_unit() => {
+                    values.push(AlgebraicValue::unit())
+                }
+                (SqlLiteral::Null, _) if ty.is_option() => {
+                    values.push(AlgebraicValue::OptionNone())
+                }
+                (SqlLiteral::Null, _) => {
+                    return Err(UnexpectedType::new(ty, &AlgebraicType::unit()).into());
+                }
                 (SqlLiteral::Bool(v), AlgebraicType::Bool) => {
                     values.push(AlgebraicValue::Bool(v));
                 }
@@ -212,6 +221,15 @@ pub fn type_update(update: SqlUpdate, tx: &impl SchemaView) -> TypingResult<Tabl
             .get_column_by_name(&field)
             .ok_or_else(|| Unresolved::field(&table_name, &field))?;
         match (lit, ty) {
+            (SqlLiteral::Null, _) if ty.is_unit() => {
+                values.push((*col_id, AlgebraicValue::unit()));
+            }
+            (SqlLiteral::Null, _) if ty.is_option() => {
+                values.push((*col_id, AlgebraicValue::OptionNone()));
+            }
+            (SqlLiteral::Null, _) => {
+                return Err(UnexpectedType::new(ty, &AlgebraicType::unit()).into());
+            }
             (SqlLiteral::Bool(v), AlgebraicType::Bool) => {
                 values.push((*col_id, AlgebraicValue::Bool(v)));
             }
@@ -286,6 +304,7 @@ pub fn type_and_rewrite_set(set: SqlSet, tx: &impl SchemaView) -> TypingResult<T
     }
 
     match lit {
+        SqlLiteral::Null => Err(UnexpectedType::new(&AlgebraicType::U64, &AlgebraicType::unit()).into()),
         SqlLiteral::Bool(_) => Err(UnexpectedType::new(&AlgebraicType::U64, &AlgebraicType::Bool).into()),
         SqlLiteral::Str(_) => Err(UnexpectedType::new(&AlgebraicType::U64, &AlgebraicType::String).into()),
         SqlLiteral::Hex(_) => Err(UnexpectedType::new(&AlgebraicType::U64, &AlgebraicType::bytes()).into()),
diff --git a/crates/sql-parser/src/ast/mod.rs b/crates/sql-parser/src/ast/mod.rs
index 776d4fc5006..50390f312be 100644
--- a/crates/sql-parser/src/ast/mod.rs
+++ b/crates/sql-parser/src/ast/mod.rs
@@ -199,6 +199,8 @@ impl From<Ident> for SqlIdent {
 /// A SQL constant expression
 #[derive(Debug)]
 pub enum SqlLiteral {
+    /// Null literal
+    Null,
     /// A boolean constant
     Bool(bool),
     /// A hex value like 0xFF or x'FF'
diff --git a/crates/sql-parser/src/parser/mod.rs b/crates/sql-parser/src/parser/mod.rs
index 9e6e5642bda..aca60c0d604 100644
--- a/crates/sql-parser/src/parser/mod.rs
+++ b/crates/sql-parser/src/parser/mod.rs
@@ -291,6 +291,7 @@ pub(crate) fn parse_binop(op: BinaryOperator) -> SqlParseResult<BinOp> {
 /// Parse a literal expression
 pub(crate) fn parse_literal(value: Value) -> SqlParseResult<SqlLiteral> {
     match value {
+        Value::Null => Ok(SqlLiteral::Null),
         Value::Boolean(v) => Ok(SqlLiteral::Bool(v)),
         Value::Number(v, _) => Ok(SqlLiteral::Num(v.into_boxed_str())),
         Value::SingleQuotedString(s) => Ok(SqlLiteral::Str(s.into_boxed_str())),