Dynamic sql in field of query

Question

Hello friends,
I have a struct bellow:
-- tanks: tanks of corporation
create table tanks
owner varchar2(6) not null,
tank_id varchar2(6) not null,
oil_volume number not null,
water_volume number not null,
availabled char(1) --> calculated. true (1), false (0)
primary key (tank_id, owner)
insert into tanks (owner, tank_id, oil_volume, water_volume)
select 'L', 'tank_A', 6, 10 from dual union
select 'L', 'tank_B', 7, 1 from dual union
select 'M' 'tank_C', 9, 7 from dual;
/* available_tank_rules:
table that defines the availability rules of a tank of corporate
if any of the rules is false, the tank's availability is also false
create table available_tank_rules
owner varchar2(6),
column_name varchar2(10),
operator_type varchar2(2),
value_ number,
primary key (owner, column_name)
alter table available_tank_rules
add constraint CK_1
check (operador_type in ('>', '>=', '<', '<=', '='));
insert into available_tank_rules (owner, column_name, operator_type, value_in_test)
select 'L', 'oil_volume', '>=', 6 from dual union
select 'L', 'water_volume', '=', 1 from dual union
select 'M', 'water_volume', '<', 3 from dual union
select from dual;
-- how to execute this expression dynamically on a sql query?
--I need this output of available_tank_rules table:
owner, tank_id , oil_volume, water_volume, availabled
'L' , 'tank_A', 6 , 10 , 0
'L' , 'tank_B', 3 , 1 , 1
'M' , 'tank_C', 9 , 7 , 0
thanks.

Answer 1

Should be possible with a method like this:
SQL> with tanks as (
select 'L' owner, 'tank_A' tank_id, 6 oil_volume, 10 water_volume from dual union
select 'L',       'tank_B',         7,             1              from dual union
select 'M',       'tank_C',         9,             7              from dual
available_tank_rules as (
select 'L' owner, 'oil_volume' column_name, '>=' operator_type, 6 value_in_test from dual union
select 'L',       'water_volume',           '=',                1               from dual union
select 'M',       'water_volume',           '<',                3               from dual
select owner,
       tank_id,
       oil_volume,
       water_volume,
       case when dbms_xmlgen.getxml('select * from dual where ' || cond) is not null then 1 else 0 end available
  from (
        select t.*,
              nvl((select t.oil_volume || operator_type || value_in_test from available_tank_rules a where t.owner=a.owner and column_name = 'oil_volume'),'1=1') || ' and ' ||
              nvl((select t.water_volume || operator_type || value_in_test from available_tank_rules a where t.owner=a.owner and column_name = 'water_volume'),'1=1') cond
          from tanks t)
O TANK_I OIL_VOLUME WATER_VOLUME  AVAILABLE
L tank_A          6           10          0
L tank_B          7            1          1
M tank_C          9            7          0but I strongly suggest to rethink your design. To store conditions and operators in a table is certainly not the way to go ...