Question

SELECT
    description
FROM 
    diagnosis_mapping 
LEFT JOIN
    diagnosis_codes
ON
    diagnosis_codes.codeid = diagnosis_mapping.codeid

SELECT
    description
FROM 
    diagnosis_mapping 
LEFT JOIN 
    diagnosis_codes
ON
    diagnosis_codes.codeid = diagnosis_mapping.secondarycodeid

How to merge these 2 queries and get info in a single resultset?
In first i need to match with codeid and in second i need to match with secondarycodeid to the same mastertable to fetch the description of both.

Answer 1

You can do two joins in one query, just give an alias to the table names so MySQL knows what you want to get:

SELECT
    a.description desc_a,
    b.description desc_b
FROM 
    diagnosis_mapping 
LEFT JOIN
    diagnosis_codes a
ON
    a.codeid = diagnosis_mapping.codeid
LEFT JOIN 
    diagnosis_codes b
ON
    b.codeid = diagnosis_mapping.secondarycodeid

In this example, a is an alias for the first diagnosis_codes table and b to the other. When you give alias names to the tables, MySQL (and any other SQL aware database) treats them basically as two separate tables and fetches data from them independently.