_SQLite_FetchTypes()

[argumentum 731]

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#include <SQLite.au3>
;~ #include <SQLite.dll.au3>

Local $hQuery, $aRow, $aNames
_SQLite_Startup()
ConsoleWrite("_SQLite_LibVersion=" & _SQLite_LibVersion() & @CRLF)
_SQLite_Open() ; open :memory: Database
_SQLite_Exec(-1, "CREATE TABLE aTest (A,B int not null unique ,C text);")
_SQLite_Exec(-1, "INSERT INTO aTest(a,b,c) VALUES ('c','2','World');")
_SQLite_Exec(-1, "INSERT INTO aTest(a,b,c) VALUES ('b','3',' ');")
_SQLite_Exec(-1, "INSERT INTO aTest(a,b,c) VALUES ('a','1','Hello');")
_SQLite_Query(-1, "SELECT _ROWID_,* FROM aTest ORDER BY a;", $hQuery)
_SQLite_FetchTypes($hQuery, $aNames) ; Read out Column Types
ConsoleWrite(StringFormat(" %-10s  %-10s  %-10s  %-10s ", $aNames[0], $aNames[1], $aNames[2], $aNames[3]) & @CRLF)
_SQLite_FetchNames($hQuery, $aNames) ; Read out Column Names
ConsoleWrite(StringFormat(" %-10s  %-10s  %-10s  %-10s ", $aNames[0], $aNames[1], $aNames[2], $aNames[3]) & @CRLF)
While _SQLite_FetchData($hQuery, $aRow) = $SQLITE_OK
    ConsoleWrite(StringFormat(" %-10s  %-10s  %-10s  %-10s ", $aRow[0], $aRow[1], $aRow[2], $aRow[3]) & @CRLF)
WEnd
_SQLite_Exec(-1, "DROP TABLE aTest;")
_SQLite_Close()
_SQLite_Shutdown()

; Output:
; INTEGER                 int         text
; rowid       A           B           C
; 3           a           1           Hello
; 2           b           3
; 1           c           2           World

Func _SQLite_FetchTypes($hQuery, ByRef $aTypes)
    Dim $aTypes[1]
    If __SQLite_hChk($hQuery, 3, False) Then Return SetError(@error, 0, $SQLITE_MISUSE)
    Local $avDataCnt = DllCall($__g_hDll_SQLite, "int:cdecl", "sqlite3_column_count", "ptr", $hQuery)
    If @error Then Return SetError(1, @error, $SQLITE_MISUSE) ; DllCall error
    If $avDataCnt[0] <= 0 Then Return SetError(-1, 0, $SQLITE_DONE)
    ReDim $aTypes[$avDataCnt[0]]
    Local $avColName
    For $iCnt = 0 To $avDataCnt[0] - 1
        $avColName = DllCall($__g_hDll_SQLite, "wstr:cdecl", "sqlite3_column_decltype16", "ptr", $hQuery, "int", $iCnt)
        If @error Then Return SetError(2, @error, $SQLITE_MISUSE) ; DllCall error
        $aTypes[$iCnt] = $avColName[0]
    Next
    Return $SQLITE_OK
EndFunc   ;==>_SQLite_FetchTypes

 If you wanna build a proper JSON string, you may want to know if is {"int":123} or {"text":"123"}
and for that, this can help, obviously only when declared in the SQLite table.

Edited March 7, 2020 by argumentum

[jchd 1,557]

Don't believe this!

You can store any type in (almost) any column of any row, you can declare fantasy types or no type at all.

The only reliable way to know which default type a result column of the current row is is to invoke sqlite3_column_type(), which returns the type of the data as it is for each value of each row. Nonetheless you can still force conversion by calling a retrieval function for another type.

A column declared INT can store the string value 'abc123' in a given row; sqlite3_column_type() would return SQLITE_TEXT but you can call sqlite3_column_blob() to force conversion to binary and retrieve the corresponding blob.

Of course the conversions you can force this way don't always make sense. A picture stored as a 3.5 Mb blob value in a column declared CHAR and retrieved with sqlite3_column_int64() is going to be deceptive.

Edited March 8, 2020 by jchd

[argumentum 731]

19 minutes ago, jchd said:

The only reliable way to know which default type a result column of the current row is is to invoke sqlite3_column_type(), which returns the type of the data as it is for each value of each row.

lol, yes, SQLite is some fantastic piece of code. The only column that'll adhere to INTEGER is the RowID. ( ...or PK if I understand that right )
But the expectation of a column defined as INT by the coder, is to pull INTegers from that column and attempt to use it as INT.
If I declare a column "MyStuffType", SQLite will return it as "MyStuffType" type in the above function.
Declarations do help organize the code, and if:

3 hours ago, argumentum said:

you wanna build a proper JSON string, you may want to know if is {"int":123} or {"text":"123"}

And that's the idea  

[jchd 1,557]

Under the assumption that correctly declared types are actually enforced by inserts and updates, then this function will work.

I only made the point to warn unsuspecting readers to fall into the trap.