MySQL String separation by comma operator

Question

I have String asdasdwdfef,rgrgtggt,weef and i want output like in table format as shown below

id      decription
1       asdasdwdfef
2       rgrgtgg         


        

Answer 1

Requirements: split a 'delimited' column into rows (a table).

Why? You can use all the SQL Aggregate functions to process the rows.

Working SQLFiddle

Related questions that use this code:

• Count number of unique characters in a string

• Can I resolve this with pure mysql? (joining on ';' separated values in a column)

I chose to use:

• table of integers (integersequence) which when 'inner joined' or 'cross joined' (same thing) to another table will generate rows which are certain to have a unique sequence number starting from 1. This is just using what RDBMS engines are required to do.

• why a table of integers?: It is small and will get loaded into the cache. It is easy to understand.

• Rather than have lots of code in the query that obscures what it actually does. I use functions that do one job. It simplifies the main query and can be tested and checked separately. I am only concerned about ease of maintenance and understanding at this point.

The example here is for one string. However, It can be easily expanded to a table of delimited strings of various sizes. The 'cross join' will create all the possible options of index starting from 1 when joining to integersequence (i really need to use another name :-/).

So, the query:

SET @StrToParse = "asdasdwdfef,rgrgtggt,weef";

/* example */
select integerseries.id,
       count_in_set(@StrToParse, ','),
       value_in_set(@StrToParse, ',', integerseries.id)
from integerseries
where integerseries.id <= count_in_set(@StrToParse, ',');

The output:

PositionOfString, CountOfCommaDelimitedStrings, StringAtThatPosition 

1                 3                             asdasdwdfef
2                 3                             rgrgtggt
3                 3                             weef

Now, how do we get those values:

I chose to use two functions:

The names are related to the mysql function 'FIND_IN_SET'.

1) The COUNT_IN_SET function: returns the count of character delimited items in the column.

CREATE FUNCTION `COUNT_IN_SET`(haystack VARCHAR(1024), 
                               delim CHAR(1)
                               ) RETURNS INTEGER
BEGIN
      RETURN CHAR_LENGTH(haystack) - CHAR_LENGTH( REPLACE(haystack, delim, '')) + 1;
END$$

2) The VALUE_IN_SET function: treats the delimited list as a one based array and returns the value at the given 'index'.

CREATE FUNCTION `VALUE_IN_SET`(haystack VARCHAR(1024), 
                               delim CHAR(1), 
                               which INTEGER
                               ) RETURNS VARCHAR(255) CHARSET utf8 COLLATE utf8_unicode_ci
BEGIN
      RETURN  SUBSTRING_INDEX(SUBSTRING_INDEX(haystack, delim, which),
                     delim,
                     -1);
END$$

The intereseries table - see (Tally tables)

CREATE TABLE `integerseries` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=500 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

/*Data for the table `integerseries` */

insert  into `integerseries`(`id`) values (1);
insert  into `integerseries`(`id`) values (2);
insert  into `integerseries`(`id`) values (3);
insert  into `integerseries`(`id`) values (4);
insert  into `integerseries`(`id`) values (5);
insert  into `integerseries`(`id`) values (6);
insert  into `integerseries`(`id`) values (7);
insert  into `integerseries`(`id`) values (8);
insert  into `integerseries`(`id`) values (9);
insert  into `integerseries`(`id`) values (10);