fix(sqlsmith): generate typed null (#7679)

Approved-By: fuyufjh

src/tests/sqlsmith/src/sql_gen/expr.rs

@@ -638,6 +638,13 @@ fn make_bin_op(func: ExprType, exprs: &[Expr]) -> Option<Expr> {
     })
 }
 
+pub(crate) fn typed_null(ty: &DataType) -> Expr {
+    Expr::Cast {
+        expr: Box::new(sql_null()),
+        data_type: data_type_to_ast_data_type(ty),
+    }
+}
+
 /// Generates a `NULL` value.
 pub(crate) fn sql_null() -> Expr {
     Expr::Value(Value::Null)

src/tests/sqlsmith/src/sql_gen/scalar.rs

@@ -21,8 +21,7 @@ use rand::Rng;
 use risingwave_common::types::DataType;
 use risingwave_sqlparser::ast::{DataType as AstDataType, Expr, Value};
 
-use crate::sql_gen::expr::sql_null;
-use crate::sql_gen::types::data_type_to_ast_data_type;
+use crate::sql_gen::expr::typed_null;
 use crate::sql_gen::SqlGenerator;
 
 impl<'a, R: Rng> SqlGenerator<'a, R> {
@@ -35,10 +34,7 @@ impl<'a, R: Rng> SqlGenerator<'a, R> {
             // NOTE(kwannoel): We generate Cast with NULL to avoid generating lots of ambiguous
             // expressions. For instance agg calls such as `max(NULL)` may be generated,
             // and coerced to VARCHAR, where we require a `NULL::int` instead.
-            return Expr::Cast {
-                expr: Box::new(sql_null()),
-                data_type: data_type_to_ast_data_type(typ),
-            };
+            return typed_null(typ);
         }
         // Scalars which may generate negative numbers are wrapped in
         // `Nested` to ambiguity while parsing.
@@ -103,7 +99,7 @@ impl<'a, R: Rng> SqlGenerator<'a, R> {
             //         .map(|typ| self.gen_simple_scalar(typ))
             //         .collect(),
             // ),
-            _ => sql_null(),
+            _ => typed_null(typ),
         }
     }