Added support for the "null" expression.

Author: RyanLamansky

SqlServerSimulator.Tests/BuiltInFunctionTests.cs

@@ -6,6 +6,8 @@ namespace SqlServerSimulator;
 [TestClass]
 public sealed class BuiltInFunctionTests
 {
+    private static object? ExecuteScalar(string commandText) => new Simulation().ExecuteScalar(commandText);
+
     private static T ExecuteScalar<T>(string commandText) where T : struct => new Simulation().ExecuteScalar<T>(commandText);
 
     [TestMethod]
@@ -16,7 +18,11 @@ public void UnrecognizedBuiltInFunction()
     }
 
     [TestMethod]
-    public void DataLength() => AreEqual(4, ExecuteScalar<int>("select datalength(1)"));
+    public void DataLengthOfNull() => IsInstanceOfType<DBNull>(ExecuteScalar("select datalength(null)"));
+
+    [TestMethod]
+    [DataRow("1", 4)]
+    public void DataLength(string input, object? output) => AreEqual(output, ExecuteScalar($"select datalength({input})"));
 
     [TestMethod]
     public void DataLengthAllCaps() => AreEqual(4, ExecuteScalar<int>("select DATALENGTH(1)"));

SqlServerSimulator.Tests/SelectTests.cs

@@ -5,7 +5,9 @@ namespace SqlServerSimulator;
 [TestClass]
 public class SelectTests
 {
-    private static DbDataReader ScalarViaReaderTest(string commandText)
+    private static object? ExecuteScalar(string commandText) => new Simulation().ExecuteScalar(commandText);
+
+    private static DbDataReader ExecuteReaderAndRead(string commandText)
     {
         var reader = new Simulation().ExecuteReader(commandText);
         Assert.IsTrue(reader.Read());
@@ -14,11 +16,14 @@ private static DbDataReader ScalarViaReaderTest(string commandText)
 
     [TestMethod]
     public void Select1ViaExecuteReaderIndexer()
-        => Assert.AreEqual(1, ScalarViaReaderTest("select 1")[0]);
+        => Assert.AreEqual(1, ExecuteReaderAndRead("select 1")[0]);
 
     [TestMethod]
     public void Select1ViaExecuteReaderGetInt32()
-        => Assert.AreEqual(1, ScalarViaReaderTest("select 1").GetInt32(0));
+        => Assert.AreEqual(1, ExecuteReaderAndRead("select 1").GetInt32(0));
+
+    [TestMethod]
+    public void Null() => Assert.IsInstanceOfType<DBNull>(ExecuteScalar("select null"));
 
     [TestMethod]
     [DataRow("SELECT @@VERSION")]

SqlServerSimulator/Parser/Expression.cs

@@ -48,6 +48,9 @@ public static Expression Parse(Simulation simulation, IEnumerator<Token> tokens,
                                     throw SimulatedSqlException.SyntaxErrorNear(name);
 
                                 return expression;
+                            case Keyword.Null:
+                                expression = new Value();
+                                continue;
                         }
                     }
 
@@ -154,6 +157,10 @@ private sealed class Value : Expression
     {
         private readonly object? value;
 
+        public Value()
+        {
+        }
+
         public Value(Numeric value)
         {
             this.value = value.Value;