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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8a5c99cdb79bd240190da0235756566539e9156b0256ed99a2fff811aa12898' 
  AND token = '16jSlAGq96QpHzd9Cionl9MRdD3wxh2BMFIPsq+/Ayc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00029

JSON explain

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