“选择计数()”很慢
我有一个包含 1,000,000 条记录的数据库和一个如下查询：
select count(code) from table1
它在本地系统上运行良好，但在网络上变得非常慢。其他查询（例如 select * from table）执行速度很快，但 select count(code) from table1 非常慢。我无法更改数据库的结构。我的数据库是Foxpro，我使用VB.NET。
有解决办法吗？
编辑：我应该编写这样的代码吗？
dim ds as new dataset
dim da as new datadapter("select count(*) from table ", connection)
da.fill(ds,"tbl1")
那么如何从数据集中获取 select count(code) from table1 呢？
或者我必须使用 LINQ 吗？
编辑2：我的意思是select count(*)和select count(code)之间的比较。
解决办法是什么？
I have a database with 1,000,000 records and a query like this:
select count(code) from table1
It works well on the local system but becomes very slow on the network. Other queries like select * from table execute quickly, but select count(code) from table1 is very slow. I can't change the database's structure. My database is Foxpro and I use VB.NET.
Is there a solution?
Edit: Should I write code like this?
dim ds as new dataset
dim da as new datadapter("select count(*) from table ", connection)
da.fill(ds,"tbl1")
Then how can I get select count(code) from table1 from the dataset?
Or do I have to use LINQ?
Edit 2: I mean the comparison between select count(*) and select count(code).
What is the solution?
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会更快。
使用
count(code)It will be faster to do
then to use
count(code).select count(code) 从表中选择“code”列，然后对它们进行计数，但 select * 只是选择它们，但不进行计数。因此，如果您比较这两者，那么逻辑上 select * 很快。
对于拥有超过 1,000,000 条记录的表，执行时间为：
select * = 0.9818625
select count(column_name) = 1.571275
The select count(code) selects the column 'code' from the table, and then counts them, but select * just selects them, but does not do the count. So if you are comparing these two then logically select * is fast.
For my table which has more than 1,000,000 records the execution time is:
select * = 0.9818625
select count(column_name) = 1.571275