Oracle select similar values [closed] - sql

Question

Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 7 years ago.
Improve this question
i have a database table with a lot of values like this: 340.13 and 232.89.
Now i want to select the value with the best match with a comparison value.
Is this possible without great effort?

Answer 1

This will match values that are within +-10% of the search value and, if there are multiple values, will find the closest match by absolute difference.
SQL Fiddle
Oracle 11g R2 Schema Setup:
CREATE TABLE TABLE_NAME ( VALUE ) AS
SELECT 340.13 FROM DUAL UNION ALL
SELECT 232.89 FROM DUAL UNION ALL
SELECT 224.73 FROM DUAL UNION ALL
SELECT 100.00 FROM DUAL;
Query 1:
WITH search_values ( search_value ) AS (
SELECT 330 FROM DUAL UNION ALL
SELECT 230 FROM DUAL
)
SELECT search_value,
value
FROM (
SELECT search_value,
value,
RANK() OVER ( PARTITION BY Search_value
ORDER BY ABS( value - search_value ) ) AS rnk
FROM table_name t
INNER JOIN
search_values v
ON ( t.value BETWEEN search_value * 0.9 AND search_value * 1.1 )
)
WHERE Rnk = 1
Results:
| SEARCH_VALUE | VALUE |
|--------------|--------|
| 230 | 232.89 |
| 330 | 340.13 |

Answer 2

This is a pretty basic and common task so here is the general approach.
First you need to decide on "best-match-criteria". Basically it as a function of value stored in row and input value. So you can implement this function and evaluate it calling something like MATCH_RATING(COLUMN, :value) for each row. Now that you have this rating for every row, you can sort rows in any way you like and filter the most fitting one (ROWNUM is great for this as are analytic functions like RANK or ROW_NUMBER).
SELECT *
FROM (
SELECT VALUE,
MATCH_RATING(VALUE, :input_value) RATING
FROM YOUR_TABLE
ORDER BY RATING DESC)
WHERE ROWNUM = 1
Then a good idea is to check whether your chosen criteria are implemented in language because if they are, using SQL features will surely be bettter performance-wise.
For example, if distance between two numbers is the only thing that concerns you, SQL will look something like this.
SELECT VALUE
FROM (
SELECT VALUE,
ABS(VALUE - :input_value) DISTANCE
FROM YOUR_TABLE
ORDER BY DISTANCE)
WHERE ROWNUM = 1
If your function assumes 0 value on some interval meaning some rows should never get into your resultset then you should also use WHERE clause filtering useless rows (WHERE MATCH_RATING(COLUMN, :value) > 0).
Back to our distance example: let's accept distance not more than 5% of input value.
SELECT VALUE
FROM (
SELECT VALUE,
ABS(VALUE - :input_value) DISTANCE
FROM YOUR_TABLE
WHERE VALUE BETWEEN 0.95 * :input_value AND 1.05 * :input_value
ORDER BY DISTANCE)
WHERE ROWNUM = 1
By the way, index on YOUR_TABLE.VALUE will surely be helpful for this example.