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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '0403be53790c033622b1da511c6fe82c901e98a9f9878e1673a030557d9a2315' 
  AND token = '7xbWSAWHGEtAxIMSwyAz6vz/XsLILafPQkvxErCs15s=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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