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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8c6f804d206dc4d9c6f2471dbbb330be63bb0256f3d6d9d4006edb0a97afc77b' 
  AND token = '3Ssj3d0nYiWPHLlniy7ssAADS2zbhPst4j6/Rm6f63E=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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