initial support for is null and is not null

will nedd some work, but just for now

lexer.cpp

@@ -104,7 +104,8 @@ namespace usql {
     bool Lexer::isRelationalOperator(TokenType token_type) {
 	    return (token_type == TokenType::equal || token_type == TokenType::not_equal ||
 		    token_type == TokenType::greater || token_type == TokenType::greater_equal ||
-		    token_type == TokenType::lesser || token_type == TokenType::lesser_equal);
+		    token_type == TokenType::lesser || token_type == TokenType::lesser_equal ||
+		    token_type == TokenType::is);
     }
 
     bool Lexer::isLogicalOperator(TokenType token_type) {
@@ -145,6 +146,8 @@ namespace usql {
 		    return TokenType::lesser;
 	    if (token == "<=")
 		    return TokenType::lesser_equal;
+	    if (token == "is")
+		    return TokenType::is;
 	    if (token == "as")
 		    return TokenType::keyword_as;
 	    if (token == "create")
@@ -321,6 +324,9 @@ namespace usql {
 		    case TokenType::lesser_equal:
 			    txt = "<=";
 			    break;
+		    case TokenType::is:
+			    txt = "is";
+			    break;
 		    case TokenType::keyword_as:
 			    txt = "as";
 			    break;

lexer.h

@@ -20,6 +20,7 @@ namespace usql {
 	greater_equal,
 	lesser,
 	lesser_equal,
+	is,
 	keyword_as,
 	keyword_create,
 	keyword_drop,

main.cpp

@@ -145,9 +145,11 @@ void debug() {
 //		    "select ticker, dimension, calendar_date, eps, dps, roa*100 as roa, roe*100 as roe, pp(revenue), netinc from sf1 where (ticker = 'AIG' or ticker = 'WFC') and dimension = 'MRY' and calendar_date > to_date('2019-01-01', '%Y-%m-%d') order by 3 desc
 //		    "select ticker, dimension, calendar_date, eps, dps, roa*100 as roa, roe*100 as roe, pp(revenue) as revenue, pp(netinc) as netinc from sf1 where (ticker = 'AIG' or ticker = 'WFC') and dimension = 'MRY' and calendar_date > to_date('2019-01-01', '%Y-%m-%d') order by 3 desc",
 		    "create table a (i integer not null, s varchar(64), f float null, d date null,  b boolean)",
-		    "insert into a (i, s, b) values(1, upper('one'), 'Y')",
+		    "insert into a (i, s, b) values(1, upper('zero'), 'Y')",
 		    "insert into a (i, s, b, f) values(1 + 10000, upper('one'), 'N', 3.1415)",
-		    "select * from a where d is null",
+		    "insert into a (i, s, f) values(2 + 10000, upper('two'), 3.1415)",
+		    "select * from a where b is null",
+		    "select * from a where b is not null",
 //		    "select * from a where b='N'",
 //		    "update a set i = i * 100, f = f + 0.01 where i > 1",
 //		    "select to_string(i, '%d.%m.%Y %H:%M:%S'), i, s from a where i < to_date('20.12.2019', '%d.%m.%Y')",

parser.cpp

@@ -472,6 +472,12 @@ namespace usql {
 			    return RelationalOperatorType::lesser;
 		    case TokenType::lesser_equal:
 			    return RelationalOperatorType::lesser_equal;
+		    case TokenType::is:
+		    	    if (m_lexer.tokenType() == TokenType::keyword_not) {
+					m_lexer.skipToken(TokenType::keyword_not);
+			    		return RelationalOperatorType::is_not;
+			    }
+			    return RelationalOperatorType::is;
 		    default:
 			    throw Exception("Unknown relational operator " + op.token_string);
 	    }

parser.h

@@ -210,7 +210,9 @@ namespace usql {
 	greater_equal,
 	lesser,
 	lesser_equal,
-	not_equal
+	not_equal,
+	is,
+	is_not
 	// like
     };
 

usql.cpp

@@ -398,7 +398,15 @@ bool USql::eval_relational_operator(const RelationalOperatorNode &filter, Table
 
 	double comparator;
 
-	if (left_value->node_type == NodeType::int_value && right_value->node_type == NodeType::int_value) {
+	if (left_value->node_type == NodeType::null_value || right_value->node_type == NodeType::null_value) {
+		bool all_null = left_value->isNull()  && right_value->node_type == NodeType::null_value ||
+				right_value->isNull() && left_value->node_type == NodeType::null_value;
+		if (filter.op == RelationalOperatorType::is)
+			return all_null;
+		if (filter.op == RelationalOperatorType::is_not)
+			return !all_null;
+		return false;
+	} else if (left_value->node_type == NodeType::int_value && right_value->node_type == NodeType::int_value) {
 		comparator = left_value->getIntegerValue() - right_value->getIntegerValue();
 	} else if ((left_value->node_type == NodeType::int_value && right_value->node_type == NodeType::float_value) ||
 		(left_value->node_type == NodeType::float_value && right_value->node_type == NodeType::int_value) ||