Fix for IS NOT NULL

internal-packages/tsql/src/query/parser.ts

@@ -1233,7 +1233,7 @@ export class TSQLParseTreeConverter implements TSQLParserVisitor<any> {
     return {
       expression_type: "compare_operation",
       left: this.visitAsExpr(ctx.columnExpr()),
-      right: { value: null } as Constant,
+      right: { expression_type: "constant", value: null } as Constant,
       op: ctx.NOT() ? CompareOperationOp.NotEq : CompareOperationOp.Eq,
     };
   }

internal-packages/tsql/src/query/printer.test.ts

@@ -320,11 +320,23 @@ describe("ClickHousePrinter", () => {
       expect(sql).toContain("isNull(");
     });
 
-    it("should handle IS NOT NULL comparisons", () => {
+    it("should handle != NULL comparisons", () => {
       const { sql } = printQuery("SELECT * FROM task_runs WHERE started_at != NULL");
 
       expect(sql).toContain("isNotNull(");
     });
+
+    it("should handle IS NULL syntax", () => {
+      const { sql } = printQuery("SELECT * FROM task_runs WHERE error IS NULL");
+
+      expect(sql).toContain("isNull(error)");
+    });
+
+    it("should handle IS NOT NULL syntax", () => {
+      const { sql } = printQuery("SELECT * FROM task_runs WHERE error IS NOT NULL");
+
+      expect(sql).toContain("isNotNull(error)");
+    });
   });
 
   describe("ORDER BY clauses", () => {

internal-packages/tsql/src/query/printer.ts

@@ -238,7 +238,9 @@ export class ClickHousePrinter {
         response = this.visitSampleExpr(node as SampleExpr);
         break;
       default:
-        throw new NotImplementedError(`Unknown expression type: ${nodeType}`);
+        throw new NotImplementedError(
+          `Unknown expression type: ${nodeType}. Node: ${JSON.stringify(node, null, 2).slice(0, 200)}`
+        );
     }
 
     this.indentLevel--;