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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5939421c9f740dd9f3a015edd62f9a876e4191b043c5da12721965844c6f4d14' 
  AND token = 'nz6JiWbM6LaCslBQjc+iMEraz1i46nyE2fYELCxtcU8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

JSON explain

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