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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c4d303d0fc23757838b86bbb1a051079af553e64fccf47efbdf32230f060db84' 
  AND token = '5J3irOgJcmydpGeh/ez2EysisMcBqlfLuCv+y/1vFqk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}