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Write select statements as expressions

  • Articolo

You can use a select statement as an expression. This type of select statement is known as an expression select statement.

  • You can't use a table buffer variable in an expression select statement.
  • The name of the table must be used in the from clause.
  • The join keyword isn't supported.
  • The table name can't be used to qualify a field name in the order by clause.
  • In a where clause, the table name must be used as a qualifier of the field.
  • You can mention only one table in an expression select statement. Therefore, subselects aren't supported as a workaround for the unsupported join keyword.
  • The only column that can be filled with data is the column that is named before the from clause in the select clause.
  • After the closing parenthesis, the name of a column is used to reference the data value.

The following expression returns the value in the AccountNum column of the first row in the CustTable table (if a row exists).

str accountNum = (select AccountNum from CustTable order by AccountNum desc).AccountNum;
info('Max AccountNum: ' + accountNum);

Here is a simpler way to achieve the same result as the previous example.

str accountNum = (select maxof(AccountNum) from CustTable).AccountNum;
info('Max AccountNum: ' + accountNum);

The following example returns the maximum RecId value of customers that aren't blocked. Here, the maxof aggregate function is used, and the RecId field is mentioned in the function. The field that is mentioned in the aggregate function must match the field name that is used to reference the data value after the closing parenthesis. Otherwise, empty data is returned.

int64 nRecId = (select maxof(RecId) from CustTable
            where CustTable.Blocked == CustVendorBlocked::No).RecId;
info("Max RecId: " + int642Str(nRecId));

In the following example, the RecId field is used to reference a data value that isn't a RecId value. The count aggregate function doesn't return a RecId value. It's a typical practice to use the RecId field with the count function.

int64 nRecId = (select count(RecId) from CustTable
            where CustTable.Blocked == CustVendorBlocked::No).RecId;
info('Count of unblocked customers: ' + int642Str(nRecId));

select statements on fields

You can use a select statement in a lookup on a field. After a select statement that fetches a record in a table, you can enter .fieldName to reference a field in the table. These select statements must be used in expressions. A normal select statement differs from a field select statement in the following way:

  • The field select statement operates directly on a table.
  • The normal select statement operates on a table buffer variable.

The following examples shows how to access fields from a select statement.

print((select CustTable order by AccountStatement).AccountStatement);

if ((select custTable where CustTable.AccountNum == '3000').CreditMax < 5000)
{
    info('This customer has a credit maximum less than $5000.');
}