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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50cff12757843f363fc855767474993c43c5ee6fdbd6da9621009d3df0941507' 
  AND token = 'ZaxXc7iLugpCZjn92YwR56IqqlxCZ3sBWkxidCT7+Rs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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