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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a521cdb5247c8976e8b1947a8d811161b35344f3473c1ee8eb205dde38d88971' 
  AND token = 'gUw2AZiFnxSvQVyfGkkdNygeoyo/uv4AX1tSB4eDy2k=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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