Convert System. Data. DataTable computing

Based on an example, this article focuses on the computing function of System. Data. able. I believe this article will be helpful for your work and learning.
Using System;
Using System. ComponentModel;
Using System. Data;
Using System. Windows. Forms;
Namespace WindowsApplication1
...{
Public partial class Form1: Form
...{
Public Form1 ()
...{
InitializeComponent ();
}
Private void button#click (object sender, EventArgs e)
...{
// Detailed description of the System. Data. DataTable computing function. retained the following information
// Test environment vs2005, c #
System. Data. DataTable table = new DataTable ();
// Calculate the constant. No initialization column is allowed.
Object test = table. Compute ("1 + 1 ","");
Console. WriteLine (test );
// Test = 2;
Test = table. Compute ("1 + 1", "false ");
Console. WriteLine (test );
// Test = 2; constant calculation is irrelevant to filter
Test = table. Compute ("abs (1 )","");
Console. WriteLine (test );
// Test = null. I do not know why this is correct, and null is returned. Other mathematical functions will carry errors.
Test = table. Compute ("2% 2 ","");
Console. WriteLine (test );
// Test = 0;
// For other functions, refer to the following calculation column.
// Initialize datatale
Table. Columns. Add ("id", typeof (string ));
Table. Columns. Add ("value", typeof (int ));
For (int I = 1; I <= 10; I ++)
...{
System. Data. DataRow dRow = table. NewRow ();
DRow ["id"] = "id" + I. ToString ();
DRow ["value"] = I;
Table. Rows. Add (dRow );
}
// Test = table. Compute ("value + 1", "true ");
/** // Throw an exception, which must be an aggregate function
*****************//
// Calculate the quantity
Test = table. Compute ("count (id)", "false ");
Console. WriteLine (test );
// Test = 0;
Test = table. Compute ("count (id)", "true ");
Console. WriteLine (test );
// Test = 10;
// Sum
Test = table. Compute ("sum (value )","");
Console. WriteLine (test );
// Test = 55;
// Test = table. Compute ("sum (id )","");
/** // Throw an exception. It cannot be a string.
// Average
Test = table. Compute ("avg (value )","");
Console. WriteLine (test );
// Test = 5;
// Minimum
Test = table. Compute ("min (value )","");
Console. WriteLine (test );
// Test = 1;
// Maximum
Test = table. Compute ("max (value )","");
Console. WriteLine (test );
// Test = 10;
// Statistical standard deviation
Test = table. Compute ("StDev (value )","");
Console. WriteLine (test );
/// Test = 3.02765035409749
// Statistical variance
Test = table. Compute ("Var (value )","");
Console. WriteLine (test );
/// Test = 9.16666666666667
// Complex computing
Test = table. Compute ("max (value)/sum (value )","");
Console. WriteLine (test );
/// Test = 0.181818181818182
************** ****/
System. Data. DataColumn column = new DataColumn ("exp1", typeof (float ));
Table. Columns. Add (column );
// Simple computing
Column. Expression = "value * 2 ";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test = 2;
// String functions
Column. Expression = "len (id )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test = 3;
// String functions
Column. Expression = "len ('' + id + '')";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test = 5;
// String functions
Column. Expression = "len (trim ('' + id + ''))";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test = 3;
// String functions
Column. Expression = "substring (id, 3, len (id)-2 )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test = 1; // The starting character position of substring is 1, not 0
// Type conversion
Column. Expression = "convert (substring (id, 3, len (id)-2), 'System. Int32") * 1.6 ";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
/// Test = 1.6;
// Equivalent to isnull of sqlserver
Column. Expression = "isnull (value, 10 )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test = 1;
// Ternary operator, equivalent to the case when of sqlserver
Column. Expression = "iif (value> 5,1000, 2000 )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
/// Test = 2000;
// Like Operator
Column. Expression = "iif (id like '% 1', 1000,2000 )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
/// Test = 1000;
// In Operator
Column. Expression = "iif (id not in ('id1'), 1000,2000 )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
/// Test = 2000;
// Nested ternary operation
Column. Expression = "iif (value>, iif (id like '% 1 ))";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
/// Test = 4000;
// Percentage of client computing in total
Column. Expression = "value/sum (value )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
/// Test = 0.01818182
// The client calculates the difference, for example, the nba regular season victory.
Column. Expression = "max (value)-value ";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test = 9
// ********************** Parent-child table calculation ************* ***********/
// Initialize the child table and parent-child table relationships
DataTable tableChild = new DataTable ();
TableChild. Columns. Add ("id", typeof (string ));
TableChild. Columns. Add ("value", typeof (int ));
System. Data. DataSet ds = new DataSet ();
Ds. Tables. Add (tableChild );
Ds. Tables. Add (table );
DataRelation relation =
New DataRelation ("relation", table. Columns ["id"], tableChild. Columns ["id"]);
Ds. Relations. Add (relation );
For (int I = 1; I <= 10; I ++)
...{
System. Data. DataRow dRow = tableChild. NewRow ();
DRow ["id"] = "id1 ";
DRow ["value"] = I;
TableChild. Rows. Add (dRow );
}
// Calculate the number of sub-table records
Column. Expression = "count (child (relation). value )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test = 10;
// Calculate the percentage of parent and child tables
Column. Expression = "value/sum (child (relation). value )";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
/// Test = 0.01818182;
// Calculate the difference between the parent and child tables. For example, the parent table is the inventory quantity, and the sub-table is the order quantity. Then, calculate the quantity to be supplemented.
Column. Expression = "iif (value-sum
(Child (relation). value)> 0, value-sum (child (relation). value ))";
Test = table. Select ("id = 'id1'") [0] ["exp1"];
Console. WriteLine (test );
// Test =-54;
// Unfortunately, no method is found to calculate the year-on-year comparison and period-over-period comparison, and the calculation Column cannot be used as a constraint.
// The End Of ***********. DataTable allows you to use your talents as much as possible to reduce complexity.
SQL statement to reduce server computing compliance.
}
}
}