Converting delimited string to multiple values in mysql

Question

I have a mysql legacy table which contains an client identifier and a list of items, the latter as a comma-delimited string. E.g. \"xyz001\", \"foo,bar,baz\". T

Answer 1

Overview

• This is to add on to the answers that suggest using UNION

Context

• MySQL 5.7

Problem

• User xyz001epo wishes to convert a single-row delimited string into multiple rows

Screenshot

• The goal is to change BEFORE into AFTER

Solution

• if the maximum number of items per single-row delimited string is known in advance, this can be accomplished using a UNION query over the known number of elements
• in this example we ignore the first element as it is considered superfluous to the output result (e.g., you have a case where all delimited strings start with some throw-away token such as http:// or something similar)

Sample code

SELECT
  tta.*
FROM
(
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',2),'/',-1)  as txtvalu
    FROM zzdemo_uu112pingasrcdata
UNION
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',3),'/',-1)  as txtvalu
    FROM zzdemo_uu112pingasrcdata
UNION
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',4),'/',-1)  as txtvalu
    FROM zzdemo_uu112pingasrcdata
UNION
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',5),'/',-1)  as txtvalu
    FROM zzdemo_uu112pingasrcdata
UNION
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',6),'/',-1)  as txtvalu
    FROM zzdemo_uu112pingasrcdata
UNION
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',7),'/',-1)  as txtvalu
    FROM zzdemo_uu112pingasrcdata
UNION
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',8),'/',-1)  as txtvalu
    FROM zzdemo_uu112pingasrcdata
UNION
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',9),'/',-1)  as txtvalu
    FROM zzdemo_uu112pingasrcdata
UNION
    SELECT
      rowid                                                              as txtname
      ,SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(fld005,'/'),'/',10),'/',-1) as txtvalu
    FROM zzdemo_uu112pingasrcdata
) as tta
WHERE 1
  AND (txtvalu is not null)
  AND (txtvalu <> '')
;;;

Complete example

• a complete example is available at the public lab space for this answer

Rationale

• for use when the transformation must be done inside MySQL instead of on the application layer
• for use when the specific user account does not have permissions to create new functions in MySQL for security or other reasons

Pitfalls

• this solution assumes a known maximum number of items per delimited string which is not always an option
• this solution requires a trailing delimiter at the end of the delimited string, or else it will not produce the desired result
• this approach is not aesthetically pleasing, it will hurt some eyes and it will hurt some feelings