MySQL LEFT JOIN performance

Question

Recently I wrote a PHP web app to gather a list of data and output it. Originally I thought the PHP code was running slow but I checked the amount of time this query takes to run and noticed it's MySQL and not PHP.

My conclusion is that I need to make indexes on these tables but I wanted to get feedback from.others before moving forward and doing that.

Here's my query:

SELECT * 
  FROM claims c
  LEFT 
  JOIN claims_data d
    ON c.claim_number = d.claim_number
  LEFT 
  JOIN merchant_category_code m
    ON c.procedure_code = m.code
  LEFT JOIN claim_log l
    ON c.claim_number = l.claim_number
  WHERE c.social_security_num = :num 
 ORDER 
    BY c.start_date DESC

Answer 1

For your QUERY, indexes are needed for each line with

ON   left and right side of = for each table, column
WHERE for each table, column
SORT BY  each table, column

spend some time with MYSQL INDEX TUTORIALS