How to replace every other instance of a particular character in a MySQL string?

Question

How to replace value in mysql column by query like, Column is options and its of type varchar(255)

From

id   options
1    A         


        

Answer 1

Not using stored procedures, I would do it in 2 steps:

1. Insert the comma at the second occurrence of the pipe character:

   update options set options = insert(options, locate('|', options, locate('|', options) + 1), 1, ',');
   

2. Insert the remaining commas - execute the query N times:

   update options set options = insert(options, locate('|', options, locate('|', options, length(options) - locate(',', reverse(options)) + 1) + 1), 1, ',');
   

   where N =

   select max(round(((length(options) - length(replace(options, '|', ''))) - 1 ) / 2) - 1) from options;
   

   (or don't bother with counting and continue to execute the query as long as it doesn't tell you "0 rows affected")

Checked with this set of data:

id   options
1    A|10|B|20|C|30
2    A|Positive|B|Negative
3    A|10|B|20|C|30|D|40|E|50|F|60
4    A|Positive|B|Negative|C|Neutral|D|Dunno

results in:

id   options
1    A|10,B|20,C|30
2    A|Positive,B|Negative
3    A|10,B|20,C|30,D|40,E|50,F|60
4    A|Positive,B|Negative,C|Neutral,D|Dunno

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(I'll provide an explanation later)