Counting number of grouped rows in mysql

Question

In a table xyz I have a row called components and a labref row which has labref number as shown here

Table xyz

labref             component
NDQA201303001         


        

Answer 1

You need to do -

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

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You can also avoid subquery as suggested by @hims056 here