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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b8488604057b990dff92a0e1342a4420c37a1f30d7b6bf2de0fd8a4909caec68' 
  AND token = 'byqRclS3c782byk1pvXQh4vAlpb+62PX10yD5QpeMDE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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