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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b68f6937513b9a80cefaf0ecfff426a7e8ae36dd8f596f40eb33ab9bd92dbe5e' 
  AND token = 'px/e+nVrv6IOMCAnhrYd1ur9qj34JEYeHTvi2sp+hhM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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