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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'f23a02622df8dd531531e13edb39c8b08c27db4016151d4d47c0b2d74fdf047d' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

JSON explain

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