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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8e51b5608821eb919dfa7d687c60159dc571f9c6eaeaa22432f825378a674f86' 
  AND token = 'QMESywVtRyv9ZWgcYABYb8WL+gf/gwAEdrefCgR1Myw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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