Storing MD5 in MySQL - mysql

Question

Instead of storing a MD5 hash in a 32-byte field, I will like to store it in a 16-byte binary field. Mysql field "TEMP_MD5" is defined as Binary(16).
The MySQL CREATE TABLE with a sample row insert is:
CREATE TABLE `mytable` (
`TEMP_MD5` binary(16) DEFAULT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
INSERT INTO mytable (TEMP_MD5) VALUES UNHEX("202cb962ac59075b964b07152d234b70") );
The sample code:
Let's say after the 16-byte binary field has been stored in the MySQL field TEMP_MD5, how do I compare this 16-byte field in Delphi code after I retrieve the value?
Is it possible to skip MySQL HEX/UNHEX internal functions, and just use Delphi code to compare the 16-byte binary field (32-byte string) in MySQL?
For example :
FDQuery1.Open( 'SELECT TEMP_MD5 from mytable;' );
if THashMD5.GetHashBytes('123') = fDQuery1.FieldByName('TEMP_MD5').VALUE then
SHOWMESSAGE('MATCHED!');
However, it seems that the values for FieldByName('TEMP_MD5').value never matched the THashMD5.GetHashString('123') value
and another way of comparing by using SELECT statement also failed
FDQuery1.Open( 'SELECT TEMP_MD5 mytable ' +
'WHERE (TEMP_MD5=:myvalue)',
[THashMD5.GetHashBytes('123')] );
above also failed to give FDQuery1.RecordCount = 1.
Basically I'm trying to compare the 16-byte Binary I stored in MySQL to a value, let's say '123' in code to see if both matches.
I'm using Delphi 10.2 moving to 10.4 next year.

Answer 1

Here is an example of code showing how to write an MD5 into your database and how to read it back and compare with a given MD5 hash:
Inserting data:
procedure TForm1.InsertDataButtonClick(Sender: TObject);
var
MD5 : TArray<Byte>;
begin
MD5 := THashMD5.GetHashBytes('123');
FDConnection1.Connected := TRUE;
FDQuery1.SQL.Text := 'INSERT INTO mytable (TEMP_MD5) VALUES(:MD5)';
FDQuery1.ParamByName('MD5').SetBlobRawData(Length(MD5), PByte(MD5));
FDQuery1.ExecSQL;
Memo1.Lines.Add('Rows affected = ' + FDQuery1.RowsAffected.ToString);
end;
Reading data back and comparing with given hash:
procedure TForm1.ReadDataButtonClick(Sender: TObject);
var
MD5 : TArray<Byte>;
MD5_123 : TArray<Byte>;
FieldMD5 : TField;
RecCnt : Integer;
begin
MD5_123 := THashMD5.GetHashBytes('123');
FDConnection1.Connected := TRUE;
// First version: get all records
// FDQuery1.SQL.Text := 'SELECT TEMP_MD5 FROM mytable';
// Second version: Get only records where TEMP_MD5 is hash('123').
FDQuery1.SQL.Text := 'SELECT TEMP_MD5 FROM mytable WHERE TEMP_MD5 = :MD5';
FDQuery1.ParamByName('MD5').SetBlobRawData(Length(MD5_123), PByte(MD5_123));
// Execute the query
FDQuery1.Open;
RecCnt := 0;
while not FDQuery1.Eof do begin
Inc(RecCnt);
FieldMD5 := FDQuery1.FieldByName('TEMP_MD5');
SetLength(MD5, FieldMD5.DataSize);
FieldMD5.GetData(MD5);
if (Length(MD5) = Length(MD5_123)) and
(CompareMem(PByte(MD5), PByte(MD5_123), Length(MD5))) then
Memo1.Lines.Add(RecCnt.ToString + ') MD5(123) = ' + MD5ToStr(MD5))
else
Memo1.Lines.Add(RecCnt.ToString + ') ' + MD5ToStr(MD5));
FDQuery1.Next;
end;
end;
As you can see reading the code, I compare the MD5 from database with given MD5 by comparing the memory containing the values (arrays of bytes).
Utility function:
function MD5ToStr(MD5 : TArray<Byte>) : String;
var
B : Byte;
begin
Result := '';
for B in MD5 do
Result := Result + B.ToHexString(2);
end;