get the maximum number that extracted from a string using mysql - php

Question

I have a table called Elements
id reference
101 AES/JN/2001
102 AMES/JN/2001
103 AES/JN/2002
104 AES/JN/2003
105 AMES/JN/2002
I want to get the maximum number from the string. If my search key word is AMES/JN I should get 2002. And If my key word is AES/JN then output should be 2003
I have tried the following code:
select max(convert(substring_index(reference,'/', -1), unsigned)) as max
FROM Elements WHERE reference like 'AES/JN/'

Answer 1

I almost agree with Shyam except for that horribly convoluted function.
I recommend this query:
SELECT SUBSTRING_INDEX(reference,'/',-1) as `max`
FROM `Elements`
WHERE reference LIKE 'AES/JN/%'
ORDER BY reference DESC
LIMIT 1
This will output a single row with with 2003 as the value in the max column.
The reason I like this method is because CONVERT() is omitted/unnecessary.
I've compared my query against Xenofexs' on my server and mine is only .0001 seconds faster -- but this is only running on the 5 rows that the OP posted. As the database volume increases, I am confident that my query's performance lead will increase.
Even if you don't care about the micro-optimization, I think this query is easier to read/comprehend because it doesn't have a function inside a function inside a function.
In fact, I believe this next query may outperform my above query:
SELECT SUBSTRING_INDEX(reference,'/',-1) as `max`
FROM `Elements`
WHERE LOCATE('AES/JN/',reference)
ORDER BY reference DESC
LIMIT 1
Because LOCATE() will be checking the leading characters from the reference column, and the targeted substring will not occur later in the string, LOCATE() has been benchmarked to outperform LIKE.
Additional reading:
MySQL LIKE vs LOCATE
For the record, here is the table that I used:
CREATE TABLE `Elements` (
`id` int(10) NOT NULL,
`reference` varchar(100) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
INSERT INTO `Elements` (`id`, `reference`) VALUES
(101, 'AES/JN/2001'),
(102, 'AMES/JN/2001'),
(103, 'AES/JN/2002'),
(104, 'AES/JN/2003'),
(105, 'AMES/JN/2002');
ALTER TABLE `Elements`
ADD PRIMARY KEY (`id`);
ALTER TABLE `Elements`
MODIFY `id` int(10) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=106;

Answer 2

Please check how "LIKE" work's.
You can use % as joker
Just change your query and add % character. And it's work
SELECT
max(
CONVERT (
substring_index(reference, '/', - 1),
UNSIGNED
)
) AS max
FROM
reference
WHERE
reference LIKE 'AES/JN/%'
Please note : LIKE 'AES/JN/%'

Answer 3

Please find below solution.
Query:
select id,reference,digits(reference) as num_values from asasas where reference like 'AMES/JN%' order by num_values DESC limit 1
You need to create one function in mysql
DELIMITER $$
DROP FUNCTION IF EXISTS `test`.`digits`$$
CREATE FUNCTION `digits`( str CHAR(32) ) RETURNS char(32) CHARSET latin1
BEGIN
DECLARE i, len SMALLINT DEFAULT 1;
DECLARE ret CHAR(32) DEFAULT '';
DECLARE c CHAR(1);
IF str IS NULL
THEN
RETURN "";
END IF;
SET len = CHAR_LENGTH( str );
REPEAT
BEGIN
SET c = MID( str, i, 1 );
IF c BETWEEN '0' AND '9' THEN
SET ret=CONCAT(ret,c);
END IF;
SET i = i + 1;
END;
UNTIL i > len END REPEAT;
RETURN ret;
END$$
DELIMITER ;
Let me know if it not works for you

Answer 4

SELECT MAX(Z.COUNT),reference FROM
(
SELECT reference,CAST(SUBSTRING_INDEX(reference, '/', -1) AS DECIMAL) count
FROM Elements where reference like 'AES/JN/%'
)Z
Try above code.
Hope this helps.