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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '42b68349e04f67b172bccfe9140915417056286e347febd39b5a9aec4b6f5a0a' 
  AND token = 't7F4pOfHjzF1AnVXp4op+4xjlltnO6z3IKVEhhEZajU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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