问ORACLE LISTAGG当子查询，没有结果?

有AB两条查询语句
A查询 
SELECT LISTAGG(COLUMN_NAME, ' ||  ') WITHIN GROUP(ORDER BY COLUMN_ID) AS full_select_sql   FROM ALL_TAB_COLUMNS  WHERE TABLE_NAME = 'MK_USER' GROUP BY TABLE_NAME;
A查询 结果  
USERNAME ||  ROLE


B查询
SELECT    t.* FROM    MK_USER  t WHERE   (XXXXX||XXXXX) LIKE '%zhang%';


将A查询结果放入B查询，成功找到数据
SELECT    t.* FROM    MK_USER  t WHERE   (USERNAME ||  ROLE) LIKE '%zhang%';

但是将A查询放入B查询当子查询，没有结果
SELECT    t.* FROM    MK_USER  t WHERE   (SELECT LISTAGG(COLUMN_NAME, ' ||  ') WITHIN GROUP(ORDER BY COLUMN_ID) AS full_select_sql   FROM ALL_TAB_COLUMNS  WHERE TABLE_NAME = 'MK_USER' GROUP BY TABLE_NAME) LIKE '%zhang%';