如何使用C＃中的sqlite max（）函数？ [英] How do I use the sqlite max() function from C#?

问题描述

我正在使用C＃/ WPF应用程序中的SQLite数据库。我有一个表有一个声明为 INTEGER UNIQUE 的列。



我从通常的<$ c执行下面的SQL脚本$ c> ExecuteReader（）代码，我得到一个结果，这是我所期望的。问题是结果总是为零。有谁知道我可能做错了什么？

I am using an SQLite database from a C#/WPF application. I have a table that has a column that is declared as INTEGER UNIQUE.

I execute the SQL script below from my usual ExecuteReader() code and I get one single result, which is what I would expect. The problem is that the result is always zero. Does anyone know what I may be doing wrong?

SELECT max( enquiry_job_number ) FROM EnquiryJobs;

我尝试过的：



查看调试器，看来该列不存在。即使我向SQL添加 AS 子句（如下所示），命名列 SQLiteDataReader.GetOrdinal（columnName）也会返回-1。 />

What I have tried:

Looking in the debugger, it appears that the column does not exist. Even if I add an AS clause to the SQL (shown below), the named column SQLiteDataReader.GetOrdinal( columnName ) returns -1.

SELECT max( enquiry_job_number ) FROM EnquiryJobs AS "ABC";

推荐答案

除了RyanDev的出色建议外，还值得注意的是，如果你使用这个SQL：

In addition to RyanDev's excellent suggestion, it's also worth noting that if you use this SQL:

SELECT max( enquiry_job_number ) FROM EnquiryJobs;

你无法从这样的DataReader访问数据：

You cannot access the data from a DataReader like this:

SQLiteDataReader.GetOrdinal( columnName )

Becaus eyou haven;'给数据列一个名称。

将来，当你返回时尝试命名列：

Becaus eyou haven;'t given the data column a name at all.
In future, try naming the column when you return it:

SELECT max( enquiry_job_number ) AS MaxJobNo FROM EnquiryJobs;

您可以按名称访问该列：

And you can access the column by name:

int max = (int) myDataReader["MaxJobNo"];

正如评论中所提到的那样使用ExecuteScalar，因为它返回第一行的第一列。



使用DataReader参见解决方案1。

As mentioned in comments use ExecuteScalar instead since it returns the first column of the first row.

And to use DataReader see Solution 1.

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