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  • Read operation according to a key
  • Comparing HPrevious and HReadPrevious
  • Various
  • Locks
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Stored procedures
Positions on the previous file record according to a browse item. The record is not read. The number of the current record is only changed when it is returned by the HRecNum function. For functions that manipulate by default the number of the current record (functions HDelete, HRead, HModify,...), the value of this number is not updated: you must use HRecNum(). For example: not to do:
HDelete(Customer)
but
HDelete(Customer, HRecNum())
The read operation is performed from the greatest to the lowest value of the browse item (see remarks for more details).
Caution: The record loaded in memory is not modified. The HFSQL variables (Customer.Name for example, which means the Name item of Customer file) are not updated.
In most cases, HPrevious is used to position in the data file during a browse loop.
Several cases may occur after the call to HPrevious:
  • the data file is empty or no record corresponds to the filter (defined by HFilter): HOut returns True.
  • the function tries to lock a record that is already locked in read-only: HErrorLock returns True and HOut returns True.

Remark: From version 19, HFSQL is the new name of HyperFileSQL.
Example
HLast(Customer, Name)
WHILE HOut() = False
        // Process the record
        HPrevious(Customer, Name)
END
Syntax
<Result> = HPrevious([<Data file> [, <Search key item>] [, <Options>]])
<Result>: Boolean
  • True if the positioning was performed,
  • False if an error occurred. This problem can be caused by:
    • a positioning problem (empty data file, ...): HFound returns False and HError returns 0.
    • an error: HError returns an integer other than 0. HErrorInfo returns more details.
<Data file>: Optional character string (with or without quotes)
Name of HFSQL data file. If this parameter corresponds to an empty string, HPrevious handles the last data file used by the last function for HFSQL management (starting with the letter H).
<Search key item>: Optional character string (with or without quotes)
Name of key item used to browse the data file. If this name is not specified, HPrevious uses the last browse item used on this file by the last HFSQL management function (starting with "H"). If this item does not exist, the best browse item is automatically used.
<Options>: Optional constant
Configures the lock and the management of duplicates performed on the record selected by HPrevious:
hLockWriteLock in write mode: the selected record can be read by another application but it cannot be modified by another application.
hLockReadWriteLock in read/write: the selected record cannot be read or modified by another application.
hLockNoNo lock (even if HStartLock was called): the record can be read or modified by another application.
hDistinctIf duplicates are found, it is used to position on a single record among the duplicates. This parameter is taken into account only if the browse is performed on a key item.
By default, all the duplicates are browsed.
OLE DBNative Connectors (Native Accesses) The lock options will have no effect if the locks are not supported by the OLE DB provider or by Native Access.
OLE DB The lock options specified by HPrevious will be ignored. The lock mode specified by HFirst or HLast will remain effective during the calls to HPrevious and HNext.
To modify the lock mode, you must use:
Native Connectors (Native Accesses) For Native Oracle Access, a different lock mode can be specified for each record. However, if a transaction was started by SQLTransaction before implementing the lock, the lock will only be released at the end of the transaction (SQLTransaction with SQLFin or SQLAnnule).
Hyper File 5.5 The lock options are ignored. Use the lock functions (HLockRecNum) kept for backward compatibility.
Remarks

Read operation according to a key

HPrevious positions on the record with the greatest key value.
The sort order is the one that was specified in the analysis for this key.

Comparing HPrevious and HReadPrevious

HPrevious does not read the record: therefore, HPrevious is faster than HReadPrevious.
HFSQLHFSQL Client/ServerHyper File 5.5OLE DBNative Connectors (Native Accesses)

Various

The current record number is returned by HRecNum.
HChangeKey is used to modify the search key while being positioned on the current record.
Reports and QueriesHFSQLHFSQL Client/ServerOLE DBNative Connectors (Native Accesses)

Locks

By default (<Options> not specified), no lock operation is performed on the record.
If a lock is requested (hLockWrite or hLockReadWrite constant), the positioning on the record will be performed only if this record is not already locked.
There is no need to specify a lock parameter if the data file is locked by HStartLock: the lock specified by HStartLock is automatically taken into account. To ignore the lock performed by HStartLock, use the hLockNo constant.
Component : wd250hf.dll
Minimum version required
  • Version 9
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