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PDP-10 Archives
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iqlv30
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dbmspg.mem
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CREATING AND EDITING A QUERY
FIND
(for DBMS data base files)
FUNCTION:
The FIND statement locates and reads a record from a DBMS data
base file.
FORMATS:
The IQL FIND DBMS verbs are modelled after the syntax of the
Codasyl DBMS FIND verbs, of which there are five variations in
the current (V5A) implementation of DBMS-10/20. Each of these
variations is called a "record selection expression", or rse, and
each variation has several options. The FIND rse's are described
in detail in the TOPS-20 Data Base Management System Programmer's
Procedures Manual. They are summarized below, along with some
comments on slight variances from the usages described in the
referenced manual.
NOTE
In IQL, the use of the FIND verb always causes a GET of
that record, unlike the Codasyl usage, wherein those are
separate functions.
1. FIND rse 1
FIND record-name USING data-item.
This rse gets the data base record which has the
direct-access data base key value given by the data-item.
The only difference from the Codasyl rse syntax is that the
record-name MUST be specified in IQL.
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CREATING AND EDITING A QUERY
2. FIND rse 2
FIND [OWNER IN set-name-1 SET OF] CURRENT OF
record-name RECORD.
set-name-2 SET.
area-name AREA.
RUN-UNIT.
This rse is used to get the "current" record, as identified
by record name, set name, area name, or RUN-UNIT. The
current record simply means the last accessed record of the
named entity, e.g. the "current of set-name" is the last
accessed record from that set, the "current of record-name"
is the last accessed record of that particlar record type,
the "current of area" is the last accessed record from that
area, and the "current of RUN-UNIT" is the last accessed
record by the query, of any type, from any area or set.
If the phrase "OWNER IN ..." is used, the record accessed is
the owner of the named current record via the set
relationship named in the OWNER phrase. The only difference
from the Codasyl rse syntax is that the keyword SET must be
given in the OWNER phrase in IQL.
3. FIND rse 3
FIND NEXT [record-name] RECORD OF set-name SET.
area-name AREA.
PRIOR
FIRST
LAST
This FIND rse is used to access records in a relative fashion
within an area or set. The NEXT record is the one following
the current record, the PRIOR record is the one preceeding
the current record, the FIRST and LAST records are at the
beginning or end, respectively. The record name is optional,
meaning that if it is not specified, the record accessed is
any record which meets the specified relation. The only
difference from the Codasyl rse syntax is that the ability to
specify a number as the relation operator is not supported
(i.e. FIND integer RECORD ...). Since this is extremely
rare in actual use, this should not be a limitation.
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CREATING AND EDITING A QUERY
This is one of the most frequently used rse's, particularily
the FIND NEXT, since it will in fact find the first record of
the set in case no previous record has been found. A very
common construct to use in queries which need to access all
of the records of some type within an area is the following:
IF FIRSTIME FIND FIRST record-name ...
ELSE FIND NEXT record-name ...
In writing queries, you should always check the ERROR-STATUS
data item, as it will be set to a non-zero value in case
there is no record satisfying the relation specified. This
will occur, for example, if all of the records in the
set/area you are accessing have been found, and there are no
more records in that set/area. This is somewhat analagous to
an "end-of-file" condition.
4. FIND rse 4
FIND OWNER RECORD OF set-name SET.
This rse is used to find the owner of the current record of
the named set. This is identical to using rse 2 if you
specified the same set names for set-name-1 and set-name-2.
5. FIND rse 5
FIND [NEXT DUPLICATE WITHIN] record-name RECORD.
This rse is used to access records which are defined as CALC
records. This is somewhat like an ISAM facility, wherein
certain fields within a record are identified as CALC (or
key) fields, and the value within these fields is used to
calculate a physical location for that record within the data
base. To use this rse, you must pre-initialize the CALC
fields with the data values of the record you wish to access,
and then issue the FIND verb. For example,
SET PERSON-NAME TO "SMITH".
FIND NAME-RECORD RECORD.
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CREATING AND EDITING A QUERY
The NEXT DUPLICATE phrase would be used to access the next
record with the same "key" value, for example the next record
containing SMITH. The schema describing the data base
defines records as having CALC fields, and allows or
prohibits the existence of duplicate key records.
A special data item is provided by IQL for use with rse 5
FIND's, in the case of a certain CALC record type occurring
in more than one area. Since the area name is used as part
of the CALC algorithm to find the record, this area name must
be provided to the DBMS run-time system. The data item
AREA-ID is used for this purpose. It is a 30 character
alpha-numeric item which must be initialized with the name of
the area which is to be used when searching for a certain
record with a certain key. If you have a record which occurs
in more than one area, and you use rse 5 without setting the
AREA-ID, you will get an error with ERROR-STATUS set to 323.
CURRENCY UPDATING:
Normally, whenever a record is accessed, the so-called "currency
indicators" are updated. This means that the record just found
is made the current record of its record type, the current record
of the area, the current record of any sets in which it is a
member, and the current record of the RUN-UNIT. In certain
applications, however, it may be desireable to suppress the
currency updates, thereby causing some previously accessed record
to remain as the current record. This is expressed by adding a
SUPPRESS phrase to the FIND rse statement, as follows:
FIND rse SUPPRESS ALL CURRENCY UPDATES.
RECORD
AREA
SET
The only difference here from the Codasyl syntax is that the
ability to give a list of individual set names for which to
suppress currency updates is not supported by IQL.
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CREATING AND EDITING A QUERY
DBMS STATUS INFORMATION:
Certain status information about the results of DBMS FIND verbs
is made available to a query in the form of special pre-defined
data items. These are:
1. ERROR-COUNT
This is a numeric data item which is set by the DBMS run-time
system whenever a FIND is executed. It is set to 0 if the
FIND was successful, and set to non-zero if the FIND failed
for any reason.
2. ERROR-STATUS
This is a numeric data item which is set by the DBMS run-time
whenever a FIND is executed. It is set to 0 if the FIND was
successful, and is set to a non-zero error code to indicate
the nature of the error. These error codes are described in
the DBMS Programmer's Manual. Most of the errors encountered
by the IQL user will be FIND errors, which are of the format
03xx, where the 03 means that this is a FIND error, and the
xx is the specific error code.
Some of the more frequently encountered errors are listed
below:
356 no record found with this data base key
(rse 1)
317/322 the specified current record does not
participate as a member of the specified set
(rse 2 and rse 4)
307/326 no record matches the specified relational
selection, or the set is empty
(rse 3)
306 no current record for the named set exists
(rse 4)
326 no record exists with these CALC values
(rse 5)
323 the value given in the AREA-ID is invalid
(rse 5)
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CREATING AND EDITING A QUERY
3. RECORD-NAME
This is an alpha-numeric data item, 30 characters long, which
contains the actual record name of the record most recently
accessed by a successful FIND, provided that currency updates
were not suppressed.
4. AREA-NAME
This is an alpha-numeric data item, 30 characters long, which
contains the actual area name of the record most recently
accessed by a successful FIND, provided that currency updates
were not suppressed.
5. CURRENT-RECORD-KEY
This is a numeric data item which contains the actual data
base key value of the record most recently accessed by a
successful FIND, provided that currency updates were not
suppressed.
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