Oracle. Select all if parameter is null else return specific item issue

Question

I need to return all records if input parameter is null.

I\'ve written a simple query

declare  
   l_sql varchar2(100);
   i number := 1;
 begin
   l_sq         


        

Answer 1

Simply use coalesce. It is the most readable and understandable way to write this. Since the logic is contained in one predicate, it's easier to maintain and remove:

select * from job where id = coalesce(:i, id)

---

As requested, a 'proof' this actually uses the index:

create table x ( id number(15) null );

create unique index x_pk on x( id );

select id
from   x
where  id = coalesce(:x, id)
; -- Uses index

select id
from   x
where  id = :x or :x is null
; -- Full table scan

Plan:

SELECT STATEMENT ALL_ROWS Cost: 1 Bytes: 13 Cardinality: 1

1 INDEX FULL SCAN INDEX (UNIQUE) X_PK Cost: 1 Bytes: 13 Cardinality: 1