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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '68abb42d639e4048ac0defb15f5ee88d39dbb391a0845fd7da0b2043e31e9720' 
  AND token = '4UVUauBQhuHJHZ1smTfTXunGA3yS814BC0ULUmjBjho=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

JSON explain

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