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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'fd699b9df2e16e0d2c4ab102931e9fe8a0fba488950d109270f2503f260b11f9' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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