How to have a select query from string datatype into numerals?

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Hi,
I have a DataTable StudentsDtb having String DataType Column roll_no
roll_no holding data's like the following

C#

1
2
3
3a
3b
4
5
6
7
8
9
10
11
11a
12
13
13a
13b

From the above data I wish to have a max(roll_no) as 13. Is I possible?

object MyComputeValue=StudetsDtb.Compute(Max(roll_no),"");??????

Thanks

What I have tried:

Tried to find a Maximum Value from a String Column DataTable

Posted 17-Jun-20 5:07am

Paramu1973

Updated 18-Jun-20 2:51am

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3 solutions

Solution 2

This is a bit clunk but should work:

SQL

SELECT MAX(
  CASE WHEN T.roll_no NOT LIKE '%[^0-9]%' THEN CAST(T.roll_no AS INT) ELSE NULL END
) 
FROM Table AS T

This will look at each entry: if there are non-numeric characters in it, it will return null, otherwise, it will convert the string into an integer. MAX() will filter out the nulls, and return the maximum integer.

The only caveat is that if you have '14a' and '14b' without '14', then 13 will be returned as the max.

Posted 17-Jun-20 5:36am

Gregory Gadow

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Maciej Los 18-Jun-20 8:54am

5ed!

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#realJSOP · Accepted Answer · 2020-06-17T05:15:00

Solution 1

try this:

SQL

select max(case when isnumeric(roll_no)=0 then 0 else roll_no end) as max_roll

if there's a chance your data will not always have a simple numeric value (in other words:

1
2
3b

you probably want to try this

SQL

SELECT MAX(SUBSTRING(string, PATINDEX('%[0-9]%', roll_no), PATINDEX('%[0-9][^0-9]%', roll_no + 't') - PATINDEX('%[0-9]%', 
                    roll_no) + 1)) AS max_roll

Posted 17-Jun-20 5:15am

#realJSOP

Updated 17-Jun-20 5:24am

v3

Comments

Paramu1973 17-Jun-20 11:25am

Hi, how to use this select statement like any codes? thanks

#realJSOP 17-Jun-20 12:06pm

I have no idea what you're asking

Maciej Los 18-Jun-20 8:54am

5ed!

Maciej Los · Accepted Answer · 2020-06-18T02:52:00

If you would like to get the highest number from c# code, check this out:

C#

DataTable dt = new DataTable();
dt.Columns.Add(new DataColumn("roll_no", typeof(string)));

dt.Rows.Add("1");
dt.Rows.Add("2");
dt.Rows.Add("3");
dt.Rows.Add("3a");
dt.Rows.Add("3b");
dt.Rows.Add("4");
dt.Rows.Add("5");
dt.Rows.Add("6");
dt.Rows.Add("7");
dt.Rows.Add("8");
dt.Rows.Add("9");
dt.Rows.Add("10");
dt.Rows.Add("11");
dt.Rows.Add("11a");
dt.Rows.Add("12");
dt.Rows.Add("13");
dt.Rows.Add("13a");
dt.Rows.Add("13b");


int highestNumber = dt.AsEnumerable()
	.Max(x=> Convert.ToInt32(Regex.Split(x.Field<string>("roll_no"), @"[a-zA-z]")[0]));
//result: 13