Build dynamic query in oracle - oracle

Question

Could you help me building a query as below?
TABLE_A
id brand color size model yn_buy
1 A blue M A -
2 A grey X C -
3 B red X B -
4 C blue S C -
TABLE_B
brand critery
A color=grey and size=X
B color=red
C size=M
I want to build a query to update table A and the answer should be:
TABLE_A
id brand color size model yn_buy
1 A blue M A N
2 A grey X C Y
3 B red X B Y
4 C blue S C N
As you can see the data on the column "critery" should be the decisor to buy or not
I'd like to use a single merge, like the following
merge into TABLE_A a
using
(
select id, brand, CASE WHEN critery THEN 'Y' ELSE 'N' END yn_buy
TABLE_A a
left join TABLE_B b ON a.brand = b.brand
) b
ON (a.id = b.id)
WHEN MATCHED THEN UPDATE set a.yn_buy = b.yn_buy
Is it possible to do something like this? maybe using execute immediate, some kind of bind...?
thank you

Answer 1

If I don't miss something in your particular case you don't need dynamic SQL - you can simply change TABLE_B structure and use static MERGE (because I don't know how complex your criteria can be this is just an illustration):
SQL> create table table_a (id, brand, color, size#, model#, tn_buy) as
2 select 1, 'A', 'blue', 'M', 'A', cast(null as varchar2(3)) from dual union all
3 select 2, 'A', 'grey', 'X', 'C', cast(null as varchar2(3)) from dual union all
4 select 3, 'B', 'red', 'X', 'B', cast(null as varchar2(3)) from dual union all
5 select 4, 'C', 'blue', 'S', 'C', cast(null as varchar2(3)) from dual
6 /
Table screated.
SQL> create table TABLE_B (brand, color, size#)
2 as
3 select 'A', 'grey', 'X' from dual union all
4 select 'B', 'red', null from dual union all
5 select 'C', null, 'M' from dual
6 /
Table created.
SQL> merge into TABLE_A a USING (
2 select a.id, a.brand, CASE
3 WHEN a.color = nvl(a.color, a.color) and a.size# = nvl(b.size#,a.size#)
4 THEN 'Y' ELSE 'N' END yn_buy FROM
5 TABLE_A a
6 left join TABLE_B b ON a.brand = b.brand
7 ) b
8 ON (a.id = b.id)
9 WHEN MATCHED THEN UPDATE set a.yn_buy = b.yn_buy
10 /
4 rows merged.
SQL> select * from table_a order by id;
ID B COLO S M YN_
---------- - ---- - - ---
1 A blue M A N
2 A grey X C Y
3 B red X B Y
4 C blue S C N
But of your criteria are difficult enough to be implemented using simple static condition, then you can use dynamic SQL:
SQL> create table TABLE_B1 (brand, criteria)
2 as
3 select 'A', q'[color='grey' and size# in ('X','M')]' from dual union all
4 select 'B', q'[color = 'red']' from dual union all
5 select 'C', q'[size#='M']' from dual
6 /
Table created.
SQL> update table_a set yn_buy = null;
4 rows updated.
SQL> commit;
Committed.
SQL> begin
2 for cur in (select brand, criteria from table_b1) loop
3 execute immediate
4 'update table_a set yn_buy = case when '||cur.criteria||
5 q'[ then 'Y' else 'N' end where brand = :1]' using cur.brand;
6 end loop;
7 end;
8 /
PL/SQL procedure completed.
SQL> select * from table_a;
ID B COLO S M YN_
---------- - ---- - - ---
1 A blue M A N
2 A grey X C Y
3 B red X B Y
4 C blue S C N