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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '26d7b780b522c4b0a8e43f01cd088cb790cf4e7f6d6fad257b28c8a496d7ac64' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

JSON explain

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