grammar: Add NULLIF(...).

Author: anse1

expr.cc

@@ -19,8 +19,10 @@ shared_ptr<value_expr> value_expr::factory(prod *p, sqltype *type_constraint)
   try {
     if (1 == d20() && p->level < d6() && window_function::allowed(p))
       return make_shared<window_function>(p, type_constraint);
-    else if (1 == d20() && p->level < d6())
+    else if (1 == d42() && p->level < d6())
       return make_shared<coalesce>(p, type_constraint);
+    else if (1 == d42() && p->level < d6())
+      return make_shared<nullif>(p, type_constraint);
     else if (d9()<3 && p->level < d6())
       return make_shared<funcall>(p, type_constraint);
     else if (d6()<3)
@@ -156,7 +158,8 @@ comparison_op::comparison_op(prod *p) : bool_binop(p)
   }
 }
 
-coalesce::coalesce(prod *p, sqltype *type_constraint) : value_expr(p)
+coalesce::coalesce(prod *p, sqltype *type_constraint, const char *abbrev)
+     : value_expr(p), abbrev_(abbrev)
 {
   auto first_expr = value_expr::factory(this, type_constraint);
   auto second_expr = value_expr::factory(this, first_expr->type);
@@ -177,7 +180,7 @@ coalesce::coalesce(prod *p, sqltype *type_constraint) : value_expr(p)
 
 void coalesce::out(std::ostream &out)
 {
-  out << "cast(coalesce(";
+  out << "cast(" << abbrev_ << "(";
   for (auto expr = value_exprs.begin(); expr != value_exprs.end(); expr++) {
     out << **expr;
     if (expr+1 != value_exprs.end())

expr.hh

@@ -66,9 +66,10 @@ struct column_reference: value_expr {
 };
 
 struct coalesce : value_expr {
+  const char *abbrev_;
   vector<shared_ptr<value_expr> > value_exprs;
   virtual ~coalesce() { };
-  coalesce(prod *p, sqltype *type_constraint = 0);
+  coalesce(prod *p, sqltype *type_constraint = 0, const char *abbrev = "coalesce");
   virtual void out(std::ostream &out);
   virtual void accept(prod_visitor *v) {
     v->visit(this);
@@ -77,6 +78,13 @@ struct coalesce : value_expr {
   }
 };
 
+struct nullif : coalesce {
+ virtual ~nullif() { };
+     nullif(prod *p, sqltype *type_constraint = 0)
+	  : coalesce(p, type_constraint, "nullif")
+	  { };
+};
+
 struct bool_expr : value_expr {
   virtual ~bool_expr() { }
   bool_expr(prod *p) : value_expr(p) { type = scope->schema->booltype; }