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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '50ca079cf553f91b812b28afc49931104769901c26070a5a84ee75734cadd776' 
  AND token = '6JdexDLuBUltEzBhyG2oixdj3xFUf1IYO38FPkGi58I=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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