Datatable's compute method and expression syntax

The compute function of datatable is powerful.

 
Public ObjectCompute (StringExpression,StringFilter );
 

Expression: the expression to be calculated.

Filter: Filter expression

Both expressions use SQL syntax, for example:

 
Table. Compute ("Sum (count)","Count> 0");
 

When our table contains the count and price columns, how should we write an expression to calculate the total amount?

Table. Compute ("Sum (count * price)","");
 

You will surely think of this calculation, but it is wrong. We should use an expression to add the amount column for each row, and then calculate the total amount:

Table. Columns. Add ("Total",Typeof(Decimal),"Count * price"); Table. Compute ("Total","");
 

The total amount can be obtained at this time.