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SQL> with t as(
2 select 'ffff' code from dual union all
3 select 'cs' from dual union all
4 select 'cs' from dual union all
5 select 'cs' from dual union all
6 select 'ffff' from dual union all
7 select 'cs' from dual
8 )
9 select max(code) from t;
/*
MAX(CODE)
---------
ffff
*/
SQL> with t as(
2 select 'ffff' code from dual union all
3 select 'cs' from dual union all
4 select 'cs' from dual union all
5 select 'cs' from dual union all
6 select 'ffff' from dual union all
7 select 'cs' from dual
8 )
9 select min(code) from t;
/*
MIN(CODE)
---------
cs
*/
SQL> select ascii('f'),ascii('c') from dual;
/*
ASCII('F') ASCII('C')
---------- ----------
102 99
*/
--102>99,所以max(code)返回'ffff',min(code)返回'cs'