Question

这是HDBC和Sqlite3。它说“CASE”附近有语法错误。但我能找到这样的。有没有？

calculateNoOfStocksTraded :: String-＆gt; Database.HDBC.Sqlite3.Connection-＆gt; IO（） calculateNoOfStocksTraded code conn = do

                                run conn " CREATE TRIGGER calcStocks \
                                           \ AFTER INSERT ON historicalData \
                                           \ FOR EACH ROW \
                                           \ BEGIN \
                                           \ CASE WHEN (SELECT COUNT(*) FROM historicalData) >= 1  THEN \
                                           \    UPDATE company \
                                           \    SET noOfStocks=(SELECT SUM(volume) FROM historicalData  WHERE companyCode= ? ) \
                                           \    WHERE code= ? ; \
                                           \ ELSE \
                                           \    UPDATE company \
                                           \    SET noOfStocks=0  \
                                           \    WHERE code= ? ; \
                                           \ END \

                                           \ END; " [toSql code,toSql code, toSql code]

                                commit conn

Answer 1

CREATE TRIGGER期望触发器的主体为update-stmt，insert-stmt，delete-stmt或select-stmt之一;所以我们需要根据其中一个重写触发器;

~~事实证明，您可以简化触发器，以便我们可以用任何内容替换CASE语法;如果count(foo.*) < 1，则必须是sum(foo.bar) = 0的情况，因此：~~

在sqlite中; count(foo.*) < 1，导致sum(foo.bar) IS NULL这是不幸的;但我们可以通过将null转换为0 coalesce()来使其做正确的事情：

CREATE TRIGGER calcStocks
AFTER INSERT ON historicalData
FOR EACH ROW
BEGIN
   UPDATE company
   SET noOfStocks=(SELECT COALESCE(SUM(volume), 0) FROM historicalData  WHERE companyCode= ? )
   WHERE code= ? ;
END

Haskell Sqlite 3 CASE语句语法错误

1 个答案: