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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b4b51fb07afcb757c800b4295cf9b603ed3b6b70e85b2d5254bce96b58b14c6b' 
  AND token = '1P2uetgmPO2Sj6CcagdRswnsPpuVbpyzbfhcI+nMisM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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