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但sql调用的还是系统函数
SQL> with
2 function g1(s varchar)
3 return varchar
4 is
5 g varchar(1):=' ';
6 begin
7 for i in 1..length(s) loop
8 if substr(s,i,1)>g then
9 g:=substr(s,i,1);
10 end if;
11 end loop;
12 return g;
13 end;
14 select g1('abz') from dual;
15 /
G1('ABZ')
-----------------------------------------
z
SQL> with
2 function greatest(s varchar)
3 return varchar
4 is
5 g varchar(1):=' ';
6 begin
7 for i in 1..length(s) loop
8 if substr(s,i,1)>g then
9 g:=substr(s,i,1);
10 end if;
11 end loop;
12 return g;
13 end;
14 select greatest('abz') from dual;
15 /
GRE
---
abz
SQL>
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