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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b6ba1ff847965e2f420ace120b5a38eae08629f9209a7a4924658c1b71a5be92' 
  AND token = 'Sa7X4iMJbdTzFf4Wb0p41cQwyOk1KMELuHvtr5TTeSM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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