count of distincts substring in query - mysql

Question

I'm trying to create a query that count (or at least retrieve) distincts occurrences of a substring in a column.
I have one column that is like this:
elem1=value1|elem2=value2|elem3=value3
I want to retrieve distincts values of elem2 and the number of ocurrences.
SELECT
substring(
column , LOCATE( 'elem2=' , column ) + $1 , $2
) AS a ,
COUNT(*) b ,
FROM
column ORDER BY a;
Thanks

Answer 1

Here's one way to achieve the specified result.
SELECT COUNT(DISTINCT SUBSTRING_INDEX(SUBSTRING_INDEX(t.col,'elem2=',-1),'|',1))
FROM t
WHERE t.col LIKE '%elem2=%'
Apparently, I misread the question (the query above returns a count of distinct values. Or, I just lost track of the specified result, while I was working on the tedious string parsing.
SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(t.col,'elem2=',-1),'|',1) AS a
, COUNT(*) AS b
FROM t
WHERE t.col LIKE '%elem2=%'
GROUP BY SUBSTRING_INDEX(SUBSTRING_INDEX(t.col,'elem2=',-1),'|',1)
ORDER BY SUBSTRING_INDEX(SUBSTRING_INDEX(t.col,'elem2=',-1),'|',1)
NOTE:
Note that SQL wasn't really designed for parsing values out of strings.
The normative relational pattern for this type of data would to create a table, with columns named elem1, elem2, elem3, and to store each separate value in a column.
For example:
CREATE TABLE t
( id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY
, elem1 VARCHAR(80)
, elem2 VARCHAR(80)
, elem3 VARCHAR(80)
);
INSERT INTO t (elem1, elem2, elem3) VALUES ('value1', 'value2', 'value3');
To get a count of distinct values in elem2 column, we'd do something like this.
SELECT COUNT(DISTINCT elem2)
FROM t
To get the distinct values of elem2 along with the count of occurrences
SELECT elem2 AS a
, COUNT(*) AS b
FROM t
GROUP BY elem2
ORDER BY elem2
That's essentially the same as the query at the beginning of my answer; the first query just has to do the parsing the 'elem2=value2' out of the string.