The while select statement in X++ is primarily used for data handling and is one of the most commonly used forms of the select statement. It allows you to iterate through multiple records that meet certain conditions and perform actions on each of them.
This type of loop resembles the standard select statement in syntax, but is prefixed with while select instead of just select.
When using while select for data manipulation, it’s typically enclosed in a transaction to maintain data integrity.
The query results are stored in a table buffer variable. If a field list is specified in the select, only those fields are accessible in the buffer.
If aggregate functions like sum, count, or avg are used, the computed results are stored in the respective fields. These aggregate functions work only on int and real data types.
The select portion of the while select loop is executed only once, right before the loop begins its first iteration. Any Boolean condition included in the while select (such as iCounter < 1) is also evaluated only a single time, which is different from the typical while loop behavior in languages like C++ or C#.
Example 1:
int iCounter = 0;
BankAccountTable xrecBAT;
while select * from xrecBAT
where iCounter < 1
{
iCounter++;
info(strFmt("%1 , %2", iCounter, xrecBAT.AccountID));
}
In this example, the loop may execute more than once even though the condition iCounter < 1 is specified—because the condition is evaluated only once, not during each loop iteration.
Example 2:
CustTable custTable;
while select custTable
order by custTable.AccountNum
where custTable.AccountNum >= '4010' && custTable.AccountNum <= '4100'
{
info(strFmt("%1 , %2", custTable.AccountNum, custTable.SalesGroup));
}
This loop prints the AccountNum and SalesGroup for each customer in the CustTable whose account number falls within the specified range.