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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51e55c8af7caddd96a28ea1ee573d25edd2950cc376662abd8acd600256557be' 
  AND token = '9EimebOMimYp8O4XxMOGfA+9AO2mcyudgv29KDqgETo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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