Update row based on conditional value, MySQL

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CREATE TEMPORARY TABLE IF NOT EXISTS contacts AS (
SELECT * FROM
(SELECT 1   AS contact_id       ,53   AS contact_score        , 'email1@xx.com' AS contact_email UNION ALL
SELECT 2   AS contact_id       ,53   AS contact_score        , 'email2@xx.com' AS contact_email  UNION ALL
SELECT 3   AS contact_id       ,4    AS contact_score        , 'email3@xx.com' AS contact_email) data);

CREATE TEMPORARY TABLE IF NOT EXISTS reputation_email_score AS (
SELECT * FROM
(SELECT 'email1@xx.com' AS email , 3 AS score UNION ALL
SELECT 'email3@xx.com' AS email , 4 AS score) data
);

CREATE TEMPORARY TABLE IF NOT EXISTS x_message_batch_4_pq AS (
SELECT * FROM
(SELECT 1 AS prequeue_contact_id UNION ALL
SELECT 2 AS prequeue_contact_id) data
);

SELECT * FROM  contacts;

UPDATE contacts a 
       JOIN x_message_batch_4_pq b 
         ON a.contact_id = b.prequeue_contact_id 
       LEFT JOIN reputation_email_score c 
              ON a.contact_email = c.email 
SET    a.contact_score = CASE 
                           WHEN c.score IS NULL THEN 2 
                           ELSE c.score 
                         END 
WHERE  a.contact_score = 53;

SELECT * FROM  contacts;


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