Storing MD5 in MySQL

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;