Insert based on existing values

Question

I have a text field with values like this (simplified): 'XXX_01', 'XXX_02', 'YYY_01'...
I need to insert values with increasing final number, for example the next 'XXX' would be 'XXX_03', so i need to check which is the current higher 'XXX_%' and add +1.
The problem comes when there are many concurrent clients, so one may read 'XXX_02' but meanwhile another client does the same and they both try to insert 'XXX_03'.
I can't use sequences cause i would need one for XXX, one for YYY... (infinite possibilities).
What would you recommend?

Answer 1

I agree, the design/data model is flawed.
An improvement would be to use parent and child table. Here is an illustration:
06:25:22 > create table parent_tb
06:25:22   2    (prefix varchar2(3),
06:25:22   3     max_child_seq number(2));
Table created.
Elapsed: 00:00:00.10
06:25:22 >
06:25:22 > alter table parent_tb add constraint parent_pk primary key(prefix);
Table altered.
Elapsed: 00:00:00.09
06:25:22 >
06:25:22 > create table child_tb
06:25:22   2    (prefix varchar2(3),
06:25:22   3     child_seq number(2),
06:25:22   4     formatted_key varchar2(6));
Table created.
Elapsed: 00:00:00.09
06:25:22 >
06:25:22 > alter table child_tb add constraint child_pk primary key(prefix, child_seq);
Table altered.
Elapsed: 00:00:00.09
06:25:22 >
06:25:22 > alter table child_tb add constraint child_parent_fk
06:25:22   2     foreign key (prefix) references parent_tb(prefix);
Table altered.
Elapsed: 00:00:00.06
06:25:22 >
06:25:22 > alter table parent_tb add constraint parent_maxchild_fk
06:25:22   2     foreign key (prefix,max_child_seq) references child_tb(prefix,child_seq)
06:25:22   3     deferrable initially deferred;
Table altered.
Elapsed: 00:00:00.12
06:25:22 >
06:25:22 >
06:25:22 > insert into parent_tb (prefix, max_child_seq) values('XXX',null);
1 row created.
Elapsed: 00:00:00.03
06:25:22 > insert into parent_tb (prefix, max_child_seq) values('YYY',null);
1 row created.
Elapsed: 00:00:00.01
06:25:22 > commit;
Commit complete.
Elapsed: 00:00:00.00
06:25:22 >
06:25:22 > declare
06:25:22   2    procedure insert_child(in_prefix in parent_tb.prefix%type) is
06:25:22   3      v_latest_seq parent_tb.max_child_seq%type;
06:25:22   4    begin
06:25:22   5      update parent_tb set max_child_seq = nvl(max_child_seq,0)+1
06:25:22   6        where prefix=in_prefix
06:25:22   7        returning max_child_seq into v_latest_seq ;
06:25:22   8      insert into child_tb(prefix, child_seq, formatted_key)
06:25:22   9        values(in_prefix,v_latest_seq,in_prefix||'_'||to_char(v_latest_seq,'FM09'));
06:25:22  10    end insert_child;
06:25:22  11  begin
06:25:22  12    insert_child('XXX');
06:25:22  13    insert_child('YYY');
06:25:22  14    insert_child('XXX');
06:25:22  15    insert_child('XXX');
06:25:22  16    commit;
06:25:22  17  end;
06:25:22  18  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.01
06:25:23 >
06:25:23 > select * from parent_tb order by prefix;
PRE MAX_CHILD_SEQ
XXX             3
YYY             1
2 rows selected.
Elapsed: 00:00:00.11
06:25:23 > select * from child_tb order by prefix, child_seq;
PRE  CHILD_SEQ FORMAT
XXX          1 XXX_01
XXX          2 XXX_02
XXX          3 XXX_03
YYY          1 YYY_01
4 rows selected.
Elapsed: 00:00:00.75