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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'e921e804bce644e68604bd38551ac2f042f4aee9e6abe4d4e2bfd92d1b06e7b6' 
  AND token = 'mDcEzWcGdVi3//RaYOWD6CgqtxpBBBhClitm0fiDBcc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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