Add long text type STRING, with a maximum length of 2GB. Usage is similar to varchar, and there is no guarantee for the performance of storing extremely long data (#6391)

be/src/exec/merge_join_node.cpp

@@ -103,6 +103,7 @@ Status MergeJoinNode::prepare(RuntimeState* state) {
 
         case TYPE_CHAR:
         case TYPE_VARCHAR:
+        case TYPE_STRING:
             _cmp_func.push_back(compare_value<StringValue>);
             break;