From 449a3cbaf7dcd1940560cde4cf69d3625556cc57 Mon Sep 17 00:00:00 2001
From: Matt Aitken <matt@mattaitken.com>
Date: Sat, 20 Dec 2025 17:42:48 +0000
Subject: [PATCH] Fix for IS NOT NULL

---
 internal-packages/tsql/src/query/parser.ts       |  2 +-
 internal-packages/tsql/src/query/printer.test.ts | 14 +++++++++++++-
 internal-packages/tsql/src/query/printer.ts      |  4 +++-
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/internal-packages/tsql/src/query/parser.ts b/internal-packages/tsql/src/query/parser.ts
index 28330e81f..05b1df052 100644
--- a/internal-packages/tsql/src/query/parser.ts
+++ b/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,
     };
   }
diff --git a/internal-packages/tsql/src/query/printer.test.ts b/internal-packages/tsql/src/query/printer.test.ts
index d8b1f1f99..e96fee5c2 100644
--- a/internal-packages/tsql/src/query/printer.test.ts
+++ b/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", () => {
diff --git a/internal-packages/tsql/src/query/printer.ts b/internal-packages/tsql/src/query/printer.ts
index 0c27bb1d8..2de1c6d08 100644
--- a/internal-packages/tsql/src/query/printer.ts
+++ b/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--;