[CALCITE-7456] Improve the conversion of try_cast function with mssql

Author: Terran

core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java

@@ -172,6 +172,13 @@ public MssqlSqlDialect(Context context) {
       final SqlWriter.Frame frame = writer.startFunCall("CEILING");
       call.operand(0).unparse(writer, leftPrec, rightPrec);
       writer.endFunCall(frame);
+    } else if (call.getKind() == (SqlKind.SAFE_CAST)) {
+      // TRY_CAST is supported but not SAFE_CAST in MS SQL
+      final SqlWriter.Frame frame = writer.startFunCall("TRY_CAST");
+      call.operand(0).unparse(writer, leftPrec, rightPrec);
+      writer.sep("as");
+      call.operand(1).unparse(writer, leftPrec, rightPrec);
+      writer.endFunCall(frame);
     } else {
       switch (call.getKind()) {
       case FLOOR:

core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java

@@ -12025,4 +12025,16 @@ public Sql schema(CalciteAssert.SchemaSpec schemaSpec) {
     sql(query).withLibrary(SqlLibrary.HIVE).withHive().ok(expectedHive);
     sql(query).withLibrary(SqlLibrary.SPARK).withSpark().ok(expectedSpark);
   }
+
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7456">[CALCITE-7456]
+   * Improve the conversion of try_cast function with mssql</a>. */
+  @Test void testTryCastWithMssql() {
+    final String query = "select TRY_CAST(\"gross_weight\" as bigint) as gross_weight_value\n"
+        + "from \"product\"";
+    final String expectedSql = "SELECT TRY_CAST([gross_weight] AS BIGINT) AS [GROSS_WEIGHT_VALUE]"
+        + "\nFROM [foodmart].[product]";
+
+    sql(query).withLibrary(SqlLibrary.MSSQL).withMssql().ok(expectedSql);
+  }
 }