Added support for 'IS NOT? NULL' clauses, added back load.sql for jus…

…t the demo.csv

sql/load.sql

@@ -0,0 +1,3 @@
+IMPORT FROM CSV FILE 'core/demo/sample.csv' INTO sample(usage double, latency
+  double, location string, version string);
+

sql/src/main/java/edu/stanford/futuredata/macrobase/sql/QueryEngine.java

@@ -22,6 +22,7 @@
 import edu.stanford.futuredata.macrobase.sql.tree.FunctionCall;
 import edu.stanford.futuredata.macrobase.sql.tree.Identifier;
 import edu.stanford.futuredata.macrobase.sql.tree.ImportCsv;
+import edu.stanford.futuredata.macrobase.sql.tree.IsNotNullPredicate;
 import edu.stanford.futuredata.macrobase.sql.tree.Literal;
 import edu.stanford.futuredata.macrobase.sql.tree.LogicalBinaryExpression;
 import edu.stanford.futuredata.macrobase.sql.tree.LogicalBinaryExpression.Type;

sql/src/main/java/edu/stanford/futuredata/macrobase/sql/tree/IsNotNullPredicate.java

@@ -18,22 +18,19 @@
 import com.google.common.collect.ImmutableList;
 import java.util.List;
 import java.util.Objects;
-import java.util.Optional;
 
-public class IsNotNullPredicate extends Expression {
+public class IsNotNullPredicate extends ComparisonExpression {
 
     private final Expression value;
 
     public IsNotNullPredicate(Expression value) {
-        this(Optional.empty(), value);
+        super(ComparisonExpressionType.NOT_EQUAL, value, new NullLiteral());
+        requireNonNull(value, "value is null");
+        this.value = value;
     }
 
     public IsNotNullPredicate(NodeLocation location, Expression value) {
-        this(Optional.of(location), value);
-    }
-
-    private IsNotNullPredicate(Optional<NodeLocation> location, Expression value) {
-        super(location);
+        super(location, ComparisonExpressionType.NOT_EQUAL, value, new NullLiteral(location));
         requireNonNull(value, "value is null");
         this.value = value;
     }

sql/src/main/java/edu/stanford/futuredata/macrobase/sql/tree/IsNullPredicate.java

@@ -18,22 +18,19 @@
 import com.google.common.collect.ImmutableList;
 import java.util.List;
 import java.util.Objects;
-import java.util.Optional;
 
-public class IsNullPredicate extends Expression {
+public class IsNullPredicate extends ComparisonExpression {
 
     private final Expression value;
 
     public IsNullPredicate(Expression value) {
-        this(Optional.empty(), value);
+        super(ComparisonExpressionType.EQUAL, value, new NullLiteral());
+        requireNonNull(value, "value is null");
+        this.value = value;
     }
 
     public IsNullPredicate(NodeLocation location, Expression value) {
-        this(Optional.of(location), value);
-    }
-
-    private IsNullPredicate(Optional<NodeLocation> location, Expression value) {
-        super(location);
+        super(location, ComparisonExpressionType.EQUAL, value, new NullLiteral(location));
         requireNonNull(value, "value is null");
         this.value = value;
     }