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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'fc3678ef77c76e349342b3c8fc31075cbbccd23751a4bbb54a30a93aa52981c8' 
  AND token = 'gx7rA4+rrnY8K9UGY64QvY51AyktFoBYweP8peAtWVQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}