Remove last, add unscan and rescan, add handle for if not exist, just gets skipped for now

sql/lexer.go

@@ -20,6 +20,7 @@ const (
 	RPAREN
 	COMMA
 
+	// Keywords
 	CREATE
 	TABLE
 
@@ -47,6 +48,8 @@ var keywords map[string]Token = map[string]Token{
 	"TEXT":       TEXT,
 	"INTEGER":    INTEGER,
 	"NULL":       NULL,
+	"IF":         IF,
+	"EXISTS":     EXISTS,
 }
 
 type Position struct {