|
|
|
|
|
HStatCalculate (Function) In french: HStatCalcule
Available only with these kinds of connection
Performs various statistical calculations on the file keys.
This function is equivalent to HAccelerateSpeed.These statistics are used when implementing a filter, creating a query or creating a view on the data file. The HFSQL engine analyzes the selection condition, then uses these statistics to define the most discriminating items that will be used to optimize iterations on data files. The statistics are used to get information about the content of the data file when they are calculated. Also, the more modifications there are to the data file after this calculation, the less faithful these statistics are to the content of the data file. The more records the data file contains, the less the modification of a single record impacts the overall statistics. Caution: function HStatCalculate blocks the data file from being written to while statistics are being calculated (the data file is scanned for each key in the data file).. Note For an efficient statistics calculation, it is necessary to perform this calculation on all data files (e.g. in the case of a multi-file query).
HStatCalculate(Customer, CustomerName)
Syntax
<Result> = HStatCalculate([<Data file> [, <Key item> [, <Option>]]])
<Result>: Boolean - True if the calculation was performed,
- False if a problem occurred (data file locked by an application for example). HError is used to identify the error.
<Data file>: Optional character string Name of the data file used. If this name is not specified, HStatCalculate will use the last data file used by the last HFSQL function (function starting with "H"). If this parameter is equal to "*" (without specifying any item), the calculation will be performed on all data files described in the current analysis (including the data files described by HDeclare, HDeclareExternal, HDescribeFile). Warning: This data file must not be blocked by an application. <Key item>: Optional character string Name of the key item used to calculate statistics. If this name is not specified or if it is equal to "*", the statistics will be calculated for all key items found in the data file. <Option>: Integer constant Option for calculating the statistics. - If this parameter is not specified, the calculation of statistics locks the data file in write mode.
- If this parameter corresponds to the hBackgroundTask constant, the statistics are calculated in background task, without locking the data file.
Important This parameter is only taken into account for HFSQL Client/Server data files. In the other cases, the data file is automatically locked while the statistics are calculated. Remarks - HStatCalculate does not close the data file.
- The statistics can also be updated by HIndex. HIndex and HStatCalculate can both be used to update the file statistics.
- In the HFSQL Classic or Client/Server data files, the statistical calculation can only be performed on the key items.
- The syntax HStatCalculate(<Data file>) is equivalent to HStatCalculate(<Data file>, "*")
- To use HStatCalculate with the data files of an HFSQL cluster, the <Option> parameter must correspond to the hBackgroundTask constant to avoid locking the cluster.
This page is also available for…
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|