Wednesday, July 4, 2018

Select Joins

Use joins to link tables so they can return values together. By default, inner joins
are created. The following table describes the types of joins available:

Join Type Use to
inner Combine records into one table only when there are
matching values in a common field.
outer Combine records into one table even if there are no matching
values in the common field.
exists Combine records from one table whenever a value exists in a
common field in another table.
notexists Combine records from one table whenever a value in a
common field in another table does not exist.

Not only is there additional syntax needed to specify what table is being joined,
but the
where clause also has to be modified. Within the where clause, the two
fields that relate the tables must be specified in addition to any other conditions
of the search. When using an inner or outer join the table buffers of both tables
are populated with the retrieved records. An exists or not exists join only
populates the first table.
Example: Using a Join
The join shown in the following code combines records from the Customer table
and the Customer transaction table to show all vouchers and dates for customer
4000.



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CustTable custTable;
CustTrans custTrans;
while select AccountNum from custTable
join custTrans
where (custTrans.AccountNum ==
custTrans.AccountNum)
&& custTrans.AccountNum =="1103"
{
   print custTable.accountNum, " 
   ",custTrans.Voucher,' ',
 date2str(custTrans.TransDate,213,1,4,2,4,2);
}
pause;

Best Regards,
Hossein Karimi

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