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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b6e0256f438e6c32d3284e8b24a63b89fa1db78546bac05a55b5eca756bbef31' 
  AND token = 'WmCXf3Kau3lO8ZMs/OO6Ib+AyusvTCALbxbtBzHNvas=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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