3 ms·

In short: * Java doesn't have rich computing libraries despite being around for decades * SPL has those libraries, and is faster than Java, despite being inte

• followSPL 3y ago
  Let’s start with an example to explain why it’s difficult to write in SQL: calculate the maximum consecutive days that a stock keeps rising. SELECT MAX(ContinuousDays) FROM (SELECT COUNT(*) ContinuousDays FROM (SELECT SUM(UpDownTag) OVER ( ORDER BY TradeDate) NoRisingDays FROM (SELECT TradeDate, CASE WHEN Price>LAG(price) OVER ( ORDER BY TradeDate) THEN 0 ELSE 1 END UpDownTag FROM Stock ) ) GROUP BY NoRisingDays ) SQL adopts a four-layer nested code, which is more complicated overall. This problem was once used as a recruitment test of our company, the pass rate was less than 20%. Since this test question was too difficult, we modified it: give the statement and ask the candidate to find its objective. Unfortunately, the pass rate was still not high. What does it tell us? It tells us that once the calculation logic becomes slightly complex, SQL will become difficult in both understanding and writing! Then, how SPL solve these? For the first example: Stock.sort(TradeDate).group@i(Price<Price[-1]).max(~.len())