github.com/matrixorigin/matrixone@v1.2.0/test/distributed/cases/function/func_string_empty.result (about)

     1  drop table if exists t1;
     2  create table t1(a varchar(255),b char(255));
     3  insert into t1 values('', 'abcd');
     4  insert into t1 values('1111', '');
     5  select empty(a),empty(b) from t1;
     6  empty(a)	empty(b)
     7  true	false
     8  false	true
     9  drop table t1;
    10  drop table if exists t1;
    11  create table t1(a varchar(255),b char(255));
    12  insert into t1 values(NULL, NULL);
    13  select empty(a),empty(b) from t1;
    14  empty(a)	empty(b)
    15  null	null
    16  drop table t1;