Stored Procedure Maximum Pattern Match

问题

This is my stored procedure in Oracle:

 CREATE OR REPLACE PROCEDURE execute_cproc (  callnum IN VARCHAR2
                                            , RESULT  OUT VARCHAR2)
 AS
   vara_val NUMBER;
   varb_val NUMBER;
 BEGIN
   SELECT a_val, b_val
     INTO vara_val, varb_val
     FROM data_table
    WHERE callnum LIKE numberpattern || '%';
 END;

If CALLNUM is 03354123 then I am getting 2 results:

03354123 like 033%
03354123 like 03354%

Both are true so I'm getting 2 results.

How to make procedure find the longest matching only, i.e. 03354123 like 03354%?

Table :

Table Name : DATA_TABLE

Columns:

NumberPattern (varchar2) : 033, 03354

a_val ( integer ) : 1, 2

b_val ( integer ) : 1, 2

回答1:

You must restructure you query. If you want to get the best or max pattern, do this:

  select  a_val, b_val 
  into vara_val, varb_val 
  from 
      (select NumberPattern , 
              a_val,
               b_val,
               rank() over(order by length(NumberPattern) desc) ranking 
         from DATA_TABLE  
         where CALLNUM  like NumberPattern  || '%' ) 
         where ranking = 1

This will set your variables vara_val and varb_val into values 2, 2 respectively. Or if you like to get the pattern as well, just declare another variable that will hold that value then edit your query to this:

    select  NumberPattern ,a_val, b_val 
    into yournew_variable,vara_val, varb_val 
    from 
      (select NumberPattern , 
              a_val,
               b_val,
               rank() over(order by length(NumberPattern) desc) ranking 
         from DATA_TABLE  
         where CALLNUM  like NumberPattern  || '%' ) 
         where ranking = 1

Here's a brief explanation: I created a subquery that consists of the NumberPattern , a_val, b_val and the rank of the NumberPattern according to its length. This will only rank patterns that exists on the CALLNUM parameter that you have provided. So for example, you got patterns 12345,1234,789 and you passed 123456789 to your CALLNUM parameter, it will only rank patterns 12345 and 1234 since your CALLNUM starts with 12345 and 1234, not with 789. Once it is ranked, I selected the NumberPattern, a_val and b_val from that subquery where the ranking is 1

回答2:

Does your suggested solution provide an answer?

What if you data contains:

03354121 03354122 03354123

These will all match 03354%. So which one is best?

Maybe there is no answer to that.

One "fix" is to sort the data in descending order and pick the first result.

回答3:

Can you do this (sorry, I have no Oracle DB to test with):

select a_val, b_val into vara_val, varb_val
  from (
    select 
        a_val, b_val, NumberPattern, row_number() as r
    from 
        DATA_TABLE 
    where 
        CALLNUM LIKE NumberPattern || '%'
    order by NumberPattern  DESC)
where r = 1;

Since I can't test, you may have to adjust the syntax.

来源：https://stackoverflow.com/questions/33251452/stored-procedure-maximum-pattern-match

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