query-performance

问题 In our product we have a generic search engine, and trying to optimze the search performance. A lot of the tables used in the queries allow null values. Should we redesign our table to disallow null values for optimization or not? Our product runs on both Oracle and MS SQL Server . 回答1: In Oracle , NULL values are not indexed, i. e. this query: SELECT * FROM table WHERE column IS NULL will always use full table scan since index doesn't cover the values you need. More than that, this query:

问题 I\'m trying to debug the source of a SQL timeout in a web application that I maintain. I have the source code of the C# code behind, so I know exactly what code is running. I have debugged the application right down to the line that executes the SQL code that times out, and I watch the query running in SQL profiler. When this query executes from the web, it times out after 30 seconds. However, when I cut/paste the query exactly as presented in Profiler, and I put it into SSMS and run it, it

问题 I\'m curious which of the following below would be more efficient? I\'ve always been a bit cautious about using IN because I believe SQL Server turns the result set into a big IF statement. For a large result set, this could result in poor performance. For small result sets, I\'m not sure either is preferable. For large result sets, wouldn\'t EXISTS be more efficient? WHERE EXISTS (SELECT * FROM Base WHERE bx.BoxID = Base.BoxID AND [Rank] = 2) vs. WHERE bx.BoxID IN (SELECT BoxID FROM Base