Oracle: Fastest Way in PL/SQL to See if Value Exists: List, VARRAY, or Temp Table

问题

UPDATE View the edits if you care to see the long original question. This is the clearer short version of the question...

I need to see if GroupA (not always GroupA, this changes each loop iteration) exists in a [list,varray,temp table, whatever] of 200 or so groups. How I store those 200 groups is totally in my control. But I want to store them in a construct that lends itself to the FASTEST "existence" checking because I will have to check this list MANY times within a loop against different values (not always GroupA). So whats fastest in PL/SQL, checking a list...

IF 'GroupA' IN ('GroupA','GroupB') THEN...

or checking a VARRAY using MEMBER OF...

IF 'GroupA' MEMBER OF myGroups THEN

or checking a VARRAY this way...

FOR i IN myGroups.FIRST .. myGroups.LAST
LOOP
    IF myGroups(i) = 'GroupA' THEN
        v_found := TRUE;
        EXIT;
    END IF;
END LOOP;

or checking associative arrays... will test this tomorrow

UPDATE: FINAL RESULTS OF TESTING FROM EVERYONE'S SUGGESTIONS Thanks all. I ran these tests, looped 10 million times and the commas separated string using a LIKE seemed to be the fastest so I guess the points have to go to @Brian McGinity (the times are in the comments below). But since the times were all so close it probably doesn't matter which method I go with. I think I'll go with the VARRAY MEMBER OF method since I can load the array with a single line of code (bulk collect) instead of having to loop a cursor to build a string (thanks @Wernfried for bringing MEMBER OF to my attention)...

comma separated list, example: ,GroupA,GroupB,GroupC,...around 200 groups... (list made by looping a cursor)

FOR i IN 1 .. 10000000 loop
    if myGroups like '%,NONE,%' then
        z:=z+1;
    end if;
end loop;
--690msec

same commas separated list (list made by looping a cursor)...

FOR i IN 1 .. 10000000 loop
    if instr(myGroups, ',NONE,') > 0 then   
        z:=z+1;
    end if;
end loop;
--818msec

varray, same 200 groups (varray made by bulk collect)...

FOR i IN 1 .. 10000000 loop
    IF 'NONE' MEMBER of myGroups THEN
        z:=z+1;
    end if;
end loop;
--780msec

associative array method suggested by @Yaroslav Shabalin (assoc. array made by looping a cursor)...

FOR i IN 1 .. 10000000 loop
    if (a_values('NONE') = 1) then
        z:=z+1;
    end if;
end loop;
--851msec

回答1:

Is myGroup a varray? If it is a string try something like:

select 1
  from dual
 where 'abc,NONE,def' like '%,NONE,%'

It is hard to follow the constraints you're working under... If at all possible, do everything inside of sql and it will be faster.

Update:

So if you're already in a plsql unit and wanted to stay in a plsql unit then the logic above would go something like this:

declare
    gp varchar2(200) := 'abc,def,NONE,higlmn,op';
  begin
    if ','||gp||',' like '%,NONE,%' then
      dbms_output.put_line('y');
    else
      dbms_output.put_line('n');
    end if;
  end;

if this itself is in a loop then, make the list once as:

declare
    gp varchar2(200)  := 'abc,def,NONE,higlmn,op';
    gp2 varchar2(200) := ',' || gp || ',';
  begin
    if g2 like '%,NONE,%' then
      dbms_output.put_line('y');
    else
      dbms_output.put_line('n');
    end if;
  end;

Also try instr which is probably faster than like:

  declare
    gp varchar2(200) := ',abc,def,NONE,hig,';
  begin
    if instr(gp, ',NONE,') > 0 then
      dbms_output.put_line('y');
    else
      dbms_output.put_line('n');
    end if;
  end;

I have no idea if this faster than the other solutions mentioned (it stands a good chance), it is something else to try.

回答2:

I did not get your full question but perhaps this function helps you: MEMBER Condition

WHERE 'groupA' MEMBER of myGroups

回答3:

Have you considered using associative arrays also formerly known as "index-by tables"? Associative arrays indexed by string are optimized for efficient lookup by implicitly using the B*-tree organization of the values. It is PL/SQL equivalent to hash tables in other programming languages.

For example if you define an array as:

type t_values is table of number index by varchar2(20);

Then assign GroupA etc. to keys and 1 to each respective value:

a_values t_values;
for c_cursor in (select ...)
loop
 a_value(c_cursor.group_name) := 1;
end loop;

When you try to access the value for non-existent index, you will get null. Whereas for any real index you have 1 returned;

(a_value('GroupA') = 1) => TRUE
(a_value('Some_not_existent_index') IS NULL) => TRUE

来源：https://stackoverflow.com/questions/21241680/oracle-fastest-way-in-pl-sql-to-see-if-value-exists-list-varray-or-temp-tabl

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