The above example has also added a new field to the Person record set
to contain that person’s mobile phone number. Note that the Telephone
field belongs to the Residence record set because that contains the telephone
number of the home,
whereas Mobile belongs to Person since mobile telephones are normally
used exclusively by one individual.
If we want to look up the name and address of a person in our recfile, we can
use recsel as before.
Because we now have more than one record set in the acquaintances.rec
file, we have to tell recsel in which record set we want to
look up
records.
We do this with the -t flag as follows:
$ recsel -t Person -P Name,Abode acquaintances.rec Alfred Nebel 42AbbeterWay Mandy Nebel 42AbbeterWay Bertram Nebel 42AbbeterWay Charles Spencer 2SerpeRise Dirk Spencer 2SerpeRise Ernest Wright ChezGrampa
This result tells us the names of all the people in the recfile, as well as
giving a concise and hopefully effective reminder telling us where they live.
However these results would not be useful to someone unacquainted with the
individuals.
They need a list of names and full addresses.
We can use recsel to produce such a list:
$ recsel -t Person -j Abode acquaintances.rec Name: Charles Spencer Dob: 4 July 1997 Email: charlie@example.com Abode_Address: 2 Serpe Rise, Little Worning, SURREY Abode_Telephone: 09876 5432109 Abode_Id: 2SerpeRise Name: Dirk Spencer Dob: 29 June 1945 Email: dirk@example.com Mobile: 0555 342123 Abode_Address: 2 Serpe Rise, Little Worning, SURREY Abode_Telephone: 09876 5432109 Abode_Id: 2SerpeRise Name: Ernest Wright Dob: 26 April 1978 Abode_Address: 1 Wanter Rise, Greater Inncombe, BUCKS Abode_Id: ChezGrampa
The -t flag we have seen before. It tells recsel that we want
to extract records of type Person.
The -j flag is new. It says that we want to perform a join.
Specifically we want to join the Person records according to their
Abode field.
In the above example, recsel displays several field names which
do not appear anywhere in the input e.g. Abode_Address.
This is the Address field in the record joined by the foreign key Abode.
In this example probably only the name and address are of interest.
The other information such as date of birth is incidental.
The foreign key Abode_Id is certainly not wanted in the output since it
is redundant.
As usual, you can use the -P or -p options to limit the fields
which will be displayed.
However the full joined field name, if appropriate, must be specified.
So the names and addresses without the other information can be retrieved thus:
$ recsel -t Person -j Abode -p Name,Abode_Address acquaintances.rec Name: Charles Spencer Abode_Address: 2 Serpe Rise, Little Worning, SURREY Name: Dirk Spencer Abode_Address: 2 Serpe Rise, Little Worning, SURREY Name: Ernest Wright Abode_Address: 1 Wanter Rise, Greater Inncombe, BUCKS