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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5e804aa71df326edee781330b3636b27552fd6d4e75b9dc29748da9c2d17fbda' 
  AND token = 'fLVaKL3d9iZCzx50Z/wC9DZs40+LT2tFsexoLwPzwt4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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