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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '839462d09cf03a1449787027f4d1d3b800bbbceaaa78c576dda3e656fc3ce621' 
  AND token = 'b+PlSkDni497iBT3FrTay87eMgavLcPtN5uubpmm+P4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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