Create unique index oracle with where clause

oracleoracle-11g

I m trying to create a unique index with where clause like this:

CREATE UNIQUE INDEX cmt_unique_sid_yid_ct
          ON COMMENTARY (source_id, year_id)
       WHERE comment_type_id = (
         select comment_type_name 
         from comment_type 
         where comment_type_name = 'Final'
       );

Getting this error :

02158. 00000 -  "invalid CREATE INDEX option"
*Cause:    An option other than COMPRESS, NOCOMPRESS, PCTFREE, INITRANS,
           MAXTRANS, STORAGE, TABLESPACE, PARALLEL, NOPARALLEL, RECOVERABLE,
           UNRECOVERABLE, LOGGING, NOLOGGING, LOCAL, or GLOBAL was specified.
*Action:   Choose one of the valid CREATE INDEX options.

I m basically trying restrict comments with type Final from comment_type table, to only one row per source/year. So scope to :

comment_type_name | source_id | year_id

How can I do this with SQL, specifically oracle?

Best Answer

No such thing in Oracle, just some workaround with function based indexes:

CREATE UNIQUE INDEX cmt_unique_sid_yid_ct
ON COMMENTARY (
  case when comment_type_name = 'Final' then source_id end,
  case when comment_type_name = 'Final' then year_id end
);

Sample query that can use this index:

select * from commentary
where 
case when comment_type_name = 'Final' then source_id end = :B1
and case when comment_type_name = 'Final' then year_id end = :B2
;

Related Solutions

Oracle – Building Dynamic WHERE Clause

This might give you an idea:

create table Customer (
  c_firstname varchar2(50),
  c_lastname  varchar2(50),
  c_userid    varchar2(50)
);

insert into Customer values ('Micky' , 'Mouse', 'mm');
insert into Customer values ('Donald', 'Duck' , 'dd');
insert into Customer values ('Peter' , 'Pan'  , 'pp');

create or replace function GetCustomer(
  FirstN    varchar2 := null,
  LastN     varchar2 := null,
  CID       varchar2 := null
) return sys_refcursor
as
  stmt varchar2(4000);
  ret sys_refcursor;
begin
  stmt := 'select * from Customer where 1=1';

  if  FirstN is not null then
      stmt := stmt || ' and c_firstname like ''%' || FirstN || '%''';
  end if;

  if  LastN is not null then
      stmt := stmt || ' and c_lastname like ''%' || LastN  || '%''';
  end if;

  if  CID is not null then
      stmt := stmt || ' and c_userid like ''%' || CID || '%''';
  end if;

  dbms_output.put_line(stmt);

  open ret for stmt;
  return ret;
end;
/

Later, in SQL*Plus:

set serveroutput on size 100000 format wrapped

declare
  c sys_refcursor;
  fn Customer.c_firstname%type;
  ln Customer.c_lastname %type;
  id Customer.c_userid   %type;
begin
  c := GetCustomer(LastN => 'u');

  fetch c into fn, ln, id;
  while  c%found loop
      dbms_output.put_line('First Name: ' || fn);
      dbms_output.put_line('Last Name:  ' || ln);
      dbms_output.put_line('user id:    ' || id);

      fetch c into fn, ln, id;
  end loop;

  close c;
end;
/

Edit: The comment is right, and the procedure is subject to SQL injection. So, in order to prevent that, you could go with bind variables such as in this modified procedure:

create or replace function GetCustomer(
  FirstN    varchar2 := null,
  LastN     varchar2 := null,
  CID       varchar2 := null
) return sys_refcursor
as
  stmt varchar2(4000);
  ret  sys_refcursor;

  type parameter_t is table of varchar2(50);
  parameters parameter_t := parameter_t();
begin
  stmt := 'select * from Customer where 1=1';

  if  FirstN is not null then
      parameters.extend;
      parameters(parameters.count) := '%' || FirstN || '%';
      stmt := stmt || ' and c_firstname like :' || parameters.count;
  end if;

  if  LastN is not null then
      parameters.extend;
      parameters(parameters.count) := '%' || LastN || '%';
      stmt := stmt || ' and c_lastname like :' || parameters.count;
  end if;

  if  CID is not null then
      parameters.extend;
      parameters(parameters.count) := '%' || CID || '%';
      stmt := stmt || ' and c_userid like :' || parameters.count;
  end if;


  if    parameters.count = 0 then
        open ret for stmt;
  elsif parameters.count = 1 then
        open ret for stmt using parameters(1);
  elsif parameters.count = 2 then
        open ret for stmt using parameters(1), parameters(2);
  elsif parameters.count = 3 then
        open ret for stmt using parameters(1), parameters(2), parameters(3);
  else  raise_application_error(-20800, 'Too many parameters');
  end   if;

  return ret;
end;
/

Note, that now, whatever the input, the select statement becomes something like select ... from ... where 1=1 and col1 like :1 and col2 :2 ... which is obviously much safer.

Oracle not using index when > used in where clause

Oracle should be able to use the statistics to determine the high and low values for any column if you are keeping them up to date:

drop table foo;
create table foo(id date primary key);
insert into foo select sysdate-level from dual connect by level<31;
select low_value, high_value from dba_tab_columns where table_name='FOO';
/*
LOW_VALUE                                    HIGH_VALUE
-------------------------------------------- ------------------------------------------ 

*/
execute dbms_stats.gather_table_stats('JDOUGLAS', 'FOO');
select low_value, high_value from dba_tab_columns where table_name='FOO';
/*
LOW_VALUE                                    HIGH_VALUE
-------------------------------------------- ------------------------------------------
786F0C0A0E0837                               787001080E0837
*/

Best Answer

Related Solutions

Oracle – Building Dynamic WHERE Clause

Oracle not using index when > used in where clause

Related Question