Counting number of grouped rows in mysql

I found the solution. So, if you want to count quantity of groups, not quantity of elements in each group, and return duplicate value to every group record in result table, you should use OVER() clause on you'r count function.

So, for example above the solution would be

SELECT component, COUNT(*) OVER() as number_of_components FROM `xyz` 
WHERE labref = 'NDQA201303001' 
GROUP BY component

I suppose that works with any query that use GROUP BY, additional info, check in the link above.

You need to do -

SELECT
    COUNT(*)
FROM
    (
        SELECT
            DISTINCT component
        FROM
            `multiple_sample_assay_abc`
        WHERE
            labref = 'NDQA201303001'
    ) AS DerivedTableAlias

---

You can also avoid subquery as suggested by @hims056 here

Try this simple query without a sub-query:

SELECT COUNT(DISTINCT component) AS TotalRows
FROM xyz
WHERE labref = 'NDQA201303001';

See this SQLFiddle