MS SQL Server compatibility: ISNULL is now an alias for IFNULL.

h2/src/main/org/h2/expression/Function.java

@@ -310,6 +310,7 @@ public class Function extends Expression implements FunctionCall {
         addFunction("DATABASE_PATH", DATABASE_PATH, 0, Value.STRING);
         addFunctionNotDeterministic("LOCK_TIMEOUT", LOCK_TIMEOUT, 0, Value.INT);
         addFunctionWithNull("IFNULL", IFNULL, 2, Value.NULL);
+        addFunctionWithNull("ISNULL", IFNULL, 2, Value.NULL);
         addFunctionWithNull("CASEWHEN", CASEWHEN, 3, Value.NULL);
         addFunctionWithNull("CONVERT", CONVERT, 1, Value.NULL);
         addFunctionWithNull("CAST", CAST, 1, Value.NULL);

h2/src/test/org/h2/test/test-1.3.txt

@@ -9755,6 +9755,12 @@ select ifnull(null, '1') x1, ifnull(null, null) xn, ifnull('a', 'b') xa from tes
 > 1  null a
 > rows: 1
 
+select isnull(null, '1') x1, isnull(null, null) xn, isnull('a', 'b') xa from test;
+> X1 XN   XA
+> -- ---- --
+> 1  null a
+> rows: 1
+
 select casewhen(null, '1', '2') xn, casewhen(1>0, 'n', 'y') xy, casewhen(0<1, 'a', 'b') xa from test;
 > XN XY XA
 > -- -- --