[SOLVED] --> [SQLite] Load extension

Seminko · March 5, 2018

In my recent project I'm downloading a bunch of data, so I decided to store it in a SQLite database. NOTE: I'm using sqlite3_x64.dll

Everything is working just fine but I'm struggling with getting the Median value. SQLite has an Average function but not a Median one.

I googled but all of the provided solutions are way above my pay-grade. After some more searching I found 'extension-functions.c' on the SQLite site where Median is included. After almost an hour of struggling I was able to successfully compile it into a DLL.

So I downloaded @jchd's SQLiteExtLoad.au3 as seen here:

But I'm getting these errors:

"Path\SQLiteExtLoad.au3"(21,40) : warning: $g_hDll_SQLite: possibly used before declaration.
    Local $RetVal = DllCall($g_hDll_SQLite,
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
"Path\SQLiteExtLoad.au3"(21,40) : error: $g_hDll_SQLite: undeclared global variable.
    Local $RetVal = DllCall($g_hDll_SQLite,
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^

So I tried, copying the function to my file and changing the DLL variable ($g_hDll_SQLite) directly to the DLL location (C:\...\.. .dll), but now this error fires

If __SQLite_hChk($hConn, 1) Then Return SetError(@error, 0, $SQLITE_MISUSE)

To be honest, I don't know what to use as the $hConn - handle of connection.

I would appreciate any help, be it getting the median using SQLite queries or getting the DLL extension loaded using AutoIt.

Thanks, S.

EDIT: well, I suspect the $hConn variable refers to the return value of the _SQLite_Open function. Well, at least now _SQLite_EnableExtensions doesn't give errors. Now I run into problems with _SQLite_LoadExtension, which gives error -1, and extended 1. Apparently the 1 constant is a generic error where other error do not apply.

BTW, anybody knows whether I need to compile the extension DLL "into" x64 when I use a x64 SQLite? That might be the problem...

EDIT2: I recompiled the dll and tried it using the SQLite3.exe and it works, so I'm confident the extension DLL has been created correctly

Edited March 5, 2018 by Seminko

user4157124 · March 5, 2018

Possible workaround to return median value from a column in SQLite:

SELECT
    avg(name_column)
FROM (
    SELECT
        name_column
    FROM
        name_table
    ORDER BY
        name_column
    LIMIT
        2 - (
            SELECT
                count(*)
            FROM
                name_table
        ) % 2
    OFFSET (
            SELECT
                (count(*) - 1) / 2
            FROM
                name_table
    )
);

Seminko · March 5, 2018

55 minutes ago, user4157124 said:

Possible workaround to return median value from a column in SQLite:

Thanks man. This works great when I need to grab median from single column.

However, I'm grouping this thing by like 7 columns.

CREATE TEMPORARY TABLE avgprices AS

    SELECT Znacka, Model, Verze, Inzerat_ID, Rok_vyroby, Najeto, Najeto_kategorie, Obsah, Obsah_updated, Palivo, Link, Popis, Cena, round(avg(Cena), 0) as Averageif, Count(*) as PocetInz
    
    FROM TableName
    
    GROUP BY Znacka, Model, Verze, Rok_vyroby, Najeto_kategorie, Obsah_updated, Palivo

Not really sure how to incorporate your code...

Despite us deviating from AutoIt, I still very much appreciate the support! Hopefully the mods won't mind that much

user4157124 · March 5, 2018

No easy way in SQLite. Example (single GROUP BY):

DROP TABLE IF EXISTS table_temp;
CREATE TEMPORARY TABLE IF NOT EXISTS table_temp AS
    SELECT
        name_group,
        name_value
    FROM
        name_table
    ORDER BY
        name_group ASC,
        name_value ASC
;
SELECT
    t1.name_group,
    t1.name_value
FROM (
    SELECT
        rowid,
        name_group,
        name_value
    FROM
        table_temp
) AS t1
JOIN (
    SELECT
        name_group,
        CAST(((min(rowid) + max(rowid)) / 2) AS INTEGER) AS rowmid
    FROM
        table_temp AS t2
    GROUP BY
        name_group
) AS t3 ON t1.rowid = t3.rowmid
;

$hConn expects handle as returned from _SQLite_Open(). Example:

#include 
#include "SQLiteExtLoad.au3"

Global Const $g_sFileDb    = @ScriptDir & '\db.sqlite'
Global Const $g_sDllExt    = @ScriptDir & '\extname.dll'
Global Const $g_sDllSQLite = _SQLite_Startup()

Global       $g_hDb        = _SQLite_Open($g_sFileDb)

_SQLite_EnableExtensions($g_hDb, 1)
_SQLite_LoadExtension($g_hDb, $g_sDllExt)

;

_SQLite_Close($g_hDb)
_SQLite_Shutdown()

Seminko · March 5, 2018

26 minutes ago, user4157124 said:

$hConn expects handle as returned from _SQLite_Open(). Example:

#include 
#include "SQLiteExtLoad.au3"

Global Const $g_sFileDb    = @ScriptDir & '\db.sqlite'
Global Const $g_sDllExt    = @ScriptDir & '\extname.dll'
Global Const $g_sDllSQLite = _SQLite_Startup()

Global       $g_hDb        = _SQLite_Open($g_sFileDb)

_SQLite_EnableExtensions($g_hDb, 1)
_SQLite_LoadExtension($g_hDb, $g_sDllExt)

;

_SQLite_Close($g_hDb)
_SQLite_Shutdown()

I'm getting away from using nested selects because it is slow as hell. But thank you for the example script.

Please check my first post, I made some updates. I figured the $hConn was returned by _SQLite_Open(), but it still doesn't work for me.

Btw, have you tried the _SQLite_EnableExtensions function? It doesn't give you errors?

Seminko · March 5, 2018

So, apparently, the partial issue was that $g_hDll_SQLite was renamed to $__g_hDll_SQLite, which I updated in JCHD's script.

Still receiving errors, though...

Error code: -1 (SQLite Reported an Error (Check @extended Value))

@extended: 1 (apparently that is a generic code)

My code:

Spoiler

#include <SQLite.au3>
#include <SQLite.dll.au3>
#include "SQLiteExtLoad.au3"

Local $aResult, $iRows, $iColumns, $iRval

Global Const $g_sFileDb    = @ScriptDir & '\test.db'
Global Const $g_sDllExt    = @ScriptDir & '\median.dll'
Global Const $g_sDllSQLite = _SQLite_Startup()

Global       $g_hDb        = _SQLite_Open($g_sFileDb)

_SQLite_EnableExtensions($g_hDb, 1)
If @error Then
    MsgBox(1, "", "error1: " & @error & " / " & @extended)
EndIf

_SQLite_LoadExtension($g_hDb, $g_sDllExt)
If @error Then
    MsgBox(1, "", "error2: " & @error & " / " & @extended)
EndIf

$iRval = _SQLite_GetTable2d(-1, "SELECT median(Time) FROM SpeedTest", $aResult, $iRows, $iColumns)

If $iRval = $SQLITE_OK Then
    _ArrayDisplay($aResult)
Else
    MsgBox(1, "SQLite Error: " & $iRval, _SQLite_ErrMsg())
EndIf

_SQLite_Close($g_hDb)
_SQLite_Shutdown()

JCHD's file updated:

Spoiler

;; SQLiteExtLoad.au3

#include-once

; #FUNCTION# ====================================================================================================================
; Name...........: _SQLite_EnableExtensions
; Description ...: Enables or disables loading of SQLite extensions
; Syntax.........: _SQLite_EnableExtensions($hConn, $Enable = 1)
; Parameters ....: $hConn       handle of connection
;                  $Enable      1 to enable (default) or 0 to disable
; Return values .: none
;                  @error Value(s):       -1 - SQLite Reported an Error (Check @extended Value)
;                  1 - Call prevented by safe mode (invalid handle)
;                  2 - Error calling SQLite API 'sqlite3_enable_load_extension'
;                  @extended Value(s): Can be compared against $SQLITE_* Constants
; Author ........: jchd
; ===============================================================================================================================

Func _SQLite_EnableExtensions($hConn, $Enable = 1)
    If __SQLite_hChk($hConn, 1) Then Return SetError(@error, 0, $SQLITE_MISUSE)
    Local $RetVal = DllCall($__g_hDll_SQLite, "int:cdecl", "sqlite3_enable_load_extension", "ptr", $hConn, "int", $Enable)
    If @error Then
        Return(SetError(2, 0, 0))
    Else
        If $RetVal[0] <> $SQLITE_OK Then Return(SetError(-1, $RetVal[0], 0))
    EndIf
EndFunc   ;==>__SQLite_EnableExtensions


; #FUNCTION# ====================================================================================================================
; Name...........: _SQLite_LoadExtension
; Description ...: Loads an SQLite extension for current connection
; Syntax.........: _SQLite_LoadExtension($hConn, $sFullPath [, $sEntry = ''])
; Parameters ....: $hConn       handle of the connection for which the extension will be loaded
;                  $sFullPath   path and name of the extension DLL
;                  $sEntry      name of entry point, defaults to 'sqlite3_extension_init'
; Return values .: none
;                  @error Value(s):       -1 - SQLite Reported an Error (Check @extended Value)
;                  1 - Call prevented by safe mode (invalid handle)
;                  2 - Error while converting path to UTF-8
;                  3 - Error calling SQLite API 'sqlite3_load_extension'
;                  @extended Value(s): Can be compared against $SQLITE_* Constants
; Author ........: jchd
; ===============================================================================================================================

Func _SQLite_LoadExtension($hConn, $sFullPath, $sEntry = 'sqlite3_extension_init')
    If __SQLite_hChk($hConn, 1) Then Return SetError(@error, 0, $SQLITE_MISUSE)
    Local $tDllPath = __SQLite_StringToUtf8Struct($sFullPath)
    If @error Then Return(SetError(2, @extended, 0))
    Local $RetVal = DllCall($__g_hDll_SQLite, "int:cdecl", "sqlite3_load_extension", _
                                                "ptr", $hConn, _
                                                "ptr", DllStructGetPtr($tDllPath), _
                                                "str", $sEntry, _
                                                "ptr", 0)
    If @error Then
        Return(SetError(3, 0, 0))
    Else
        If $RetVal[0] <> $SQLITE_OK Then Return(SetError(-1, $RetVal[0], 0))
    EndIf
EndFunc   ;==>_SQLiteLoadExtension


; #FUNCTION# ====================================================================================================================
; Name...........: _SQLite_LoadAutoExtension
; Description ...: Permanently loads an SQLite extension for current session
; Syntax.........: _SQLite_LoadAutoExtension($sFullPath [, $sEntry = ''])
; Parameters ....: $sDllPath    path of the extension DLL
;                  $sEntry      optional name of entry point, defaults to 'sqlite3_extension_init'
; Return values .: none
;                  @error Value(s):       -1 - SQLite Reported an Error (Check @extended Value)
;                  1 - Error while loading extension DLL
;                  2 - Error obtaining address of named entry point
;                  3 - Error calling SQLite API 'sqlite3_auto_extension'
;                  @extended Value(s): Can be compared against $SQLITE_* Constants
; Author ........: jchd
; ===============================================================================================================================

Func _SQLite_LoadAutoExtension($sFullPath, $sEntry = 'sqlite3_extension_init')
    Local $RetVal = DllCall("kernel32.dll", "ptr", "LoadLibraryW", "wstr", $sFullPath)
    If (@error Or $RetVal[0] = 0) Then Return(SetError(1, 0, 0))
    $RetVal = DllCall('kernel32.dll', 'ptr', 'GetProcAddress', 'ptr', $RetVal[0], 'str', $sEntry)
    If (@error Or $RetVal[0] = 0) Then Return(SetError(2, 0, 0))
    $RetVal = DllCall($__g_hDll_SQLite, "none:cdecl", "sqlite3_auto_extension", "ptr", $RetVal[0])
    If @error Then
        Return(SetError(3, 0, 0))
    Else
        If $RetVal[0] <> $SQLITE_OK Then Return(SetError(-1, $RetVal[0], 0))
    EndIf
EndFunc   ;==>_SQLite_LoadAutoExtension

Edited March 5, 2018 by Seminko

Seminko · March 5, 2018

UPDATE:

The issue got solved. I incorrectly compiled the median.dll. It seems that despite me using MinGQ-W64, I somehow messed up the install and the compiled DLL ended up being 32bit (I'm using a 64bit SQLite DLL).

I re-installed MinGQ-W64, recompiled the DLL and it works now.

For all of you having issues with JCHD's SQLiteExtLoad.au3, replace '$g_hDll_SQLite' with '$__g_hDll_SQLite'.

Thanks for you help mr. @user4157124

Edited March 6, 2018 by Seminko

jchd · March 6, 2018

You're correct. The posted script dates from ages and x64 wasn't popular at this time. Also x64 is often slower than x86 in many use cases.

The global naming convention changed in the meantime.

About subqueries: are you sure you have created convenient indices? Try prepending EXPLAIN QUERY PLAN to you query and look at the output to see if any new index can speed up things.

Seminko · March 6, 2018

17 minutes ago, jchd said:

You're correct. The posted script dates from ages and x64 wasn't popular at this time. Also x64 is often slower than x86 in many use cases.

The global naming convention changed in the meantime.

About subqueries: are you sure you have created convenient indices? Try prepending EXPLAIN QUERY PLAN to you query and look at the output to see if any new index can speed up things.

Thanks for the reply.

Since the median extension works now, there is no need to dabble into the queries. It works great and is pretty fast .

Edited March 6, 2018 by Seminko

jchd · March 6, 2018

Fine. This advice is nevertheless quite generic and helps to find optimization clues.

Seminko · March 6, 2018

2 minutes ago, jchd said:

Fine. This advice is nevertheless quite generic and helps to find optimization clues.

I will make sure to look into it!

[SOLVED] --> [SQLite] Load extension

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