MySQL 5.6

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SELECT *
FROM customer
UNION ALL
SELECT
  CONCAT(id, '_1') AS id,
  COALESCE(
    (SELECT old_value
     FROM audit_log
     WHERE id = (
       SELECT MIN(id)
       FROM audit_log WHERE entity_id = c.id AND property = 'name')
    ),
    c.name)
  AS name,
  COALESCE(
    (SELECT old_value
     FROM audit_log
     WHERE id = (
       SELECT MIN(id)
       FROM audit_log WHERE entity_id = c.id AND property = 'surname')
    ),
    c.surname)
  AS surname,
  COALESCE(
    (SELECT old_value
     FROM audit_log
     WHERE id = (
       SELECT MIN(id)
       FROM audit_log WHERE entity_id = c.id AND property = 'dob')
    ),
    c.dob)
  AS dob,
  COALESCE(
    (SELECT old_value
     FROM audit_log
     WHERE id = (
       SELECT MIN(id)
       FROM audit_log WHERE entity_id = c.id AND property = 'email')
    ),
    c.email)
  AS email,
  COALESCE(
    (SELECT old_value
     FROM audit_log
     WHERE id = (
       SELECT MIN(id)
       FROM audit_log WHERE entity_id = c.id AND property = 'telephone')
    ),
    c.telephone)
  AS telephone
FROM customer c
WHERE EXISTS (SELECT * FROM audit_log WHERE entity_id = c.id)

id	name	surname	dob	email	telephone
10	Steve	Bobbly	1970-01-01	uvw@xyz.com	0123456789
15	James	Bond	1950-01-01	007@bond.com	0101010999
10_1	John	Bobbly	1970-01-01	abc@def.com