问题
I am using the following code in ACCESS 2010 to rank ~30000 rows from a table. However it takes around 15 minutes to do the ranking (I have to do this for 5 more columns and it could easily take more than an hour). I need these columns for further processing and hence tried creating a new table. I have also tried appending and updating to existing tables. Everything takes the same time. Am I missing something obvious here that could make it work faster?
SELECT MasterTable.Sales, (SELECT Count(*)+1 as HowMany
From MasterTable AS Dupe
WHERE Dupe.Sales > MasterTable.Sales) AS SalesRank INTO tableRank
FROM MasterTable;
Details on the MasterTable:
11 columns. 1 primary key (Text). 5 parameters (Sales SalesQty Profit Hits Cost, all numeric). Ranks of 5 parameters(like SalesRank and so on)
30,000 rows
回答1:
Did you try a left join with grouping?
SELECT
m1.Sales,
COUNT(*) AS HowMany
FROM
MasterTable AS m1
LEFT JOIN MasterTable m2 ON m1.Sales <= m2.Sales
GROUP BY
m1.Sales
来源：https://stackoverflow.com/questions/30848800/making-the-ranking-query-efficient