Question

I have a nice MySQL table like this:

CREATE TABLE IF NOT EXISTS BLOBTest(Id INT PRIMARY KEY AUTO_INCREMENT,

    Data BLOB);

And inside it I have the following:

SELECT HEX(Data) from BLOBTest;

+----------------------------------+
| HEX(Data)                        |
+----------------------------------+
| E764DF04463B55E9E2305934266227A1 |
+----------------------------------+

Translated, I have a table with 1 row and two columns (Id and Data). This row holds byte[] data, the byte[] array stored is the following:
[-25, 100, -33, 4, 70, 59, 85, -23, -30, 48, 89, 52, 38, 98, 39, -95]

How do I make a query to get the entire how?
At first I tried:

SELECT * FROM BLOBTest WHERE Data='[-25, 100, -33, 4, 70, 59, 85, -23, -30, 48, 89, 52, 38, 98, 39, -95]';

However this approach does not work at all, it always returns an empty set. I need to get all the information of that row and all I have is the byte[] value. How do I do it?

Thanks for any help if possible plz.

EDIT:

Here is the code of the java app and what it does.

public Map<Integer, String> queryAuthor(String author) throws Exception{

    //encrypts the name of the author
    byte[] cipheredName = cryptManager.encrypt(keyBytes, 
                author.getBytes());

    //queries db for encrypted name
    pst = con.prepareStatement("SELECT * FROM BLOBTest WHERE DATA='" + cipheredName+"'");

    //builds a map for clients to use with the information from the query. 
    ResultSet rs =  pst.executeQuery();
    Map<Integer, String> result = new HashMap<Integer, String>();
    while (rs.next()) {

        byte[] recoveredBytes = rs.getBytes(2);

        byte[] recoveredName = cryptManager.decrypt(keyBytes, 
                    recoveredBytes);

        result.put(rs.getInt(1), new String(recoveredName));

    }

    return result;
}

The problem is that making:

SELECT * FROM BLOBTest WHERE Data='[-25, 100, -33, 4, 70, 59, 85, -23, -30, 48, 89, 52, 38, 98, 39, -95]';

Returns an empty set, thus making the variable “rs” empty and therefore the returned map is empty. Everyone is sad because I’m a noob and can’t make a simple query like this =(

Answer 1

You can send the raw bytes to MySQL as a string literal:

SELECT * FROM BLOBTest WHERE Data = '????????????????'

(Since not all of your bytes can be represented by printable characters, I haven’t even tried).

This is particularly easy to do if you pass your data by way of a parameter to a prepared statement (which you really should be doing in any event):

pst = con.prepareStatement("SELECT * FROM BLOBTest WHERE DATA = ?");
pst.setBytes(1, cipheredName);

Otherwise you must be careful to ensure that you escape any bytes that MySQL would parse as string termination quotes, as they will otherwise corrupt your query.

---

^{(The following predates the additional information provided in the OP’s edit)}

If that had not been possible, it’d probably have indicated that you shouldn’t be storing your data in a BLOB-type column; for example, 16 TINYINT SIGNED columns might have been more appropriate.

Even so, there are still possibilities:

• If you can use Hexadecimal Literal in MariaDB or MySQL , which interprets the hex string to its binary form :

    SELECT * FROM BLOBTest WHERE Data = x'E764DF04463B55E9E2305934266227A1'
  

See it on sqlfiddle.

• UNHEX() also does the same thing as described in Hexadecimal Literal above :

  SELECT * FROM BLOBTest WHERE Data = UNHEX('E764DF04463B55E9E2305934266227A1')
  

• If you can convert each byte to its unsigned value:

    SELECT * FROM BLOBTest WHERE Data = CHAR(
      231,100,223,4,70,59,85,233,226,48,89,52,38,98,39,161
    )
  

See it on sqlfiddle.

• Otherwise, you will need to strip the highest order bits as MySQL treats each input to CHAR() as a 4-byte integer:

    SELECT * FROM BLOBTest WHERE Data = CHAR(
      -25 & 0xff,
      100 & 0xff,
      -33 & 0xff,
        4 & 0xff,
       70 & 0xff,
       59 & 0xff,
       85 & 0xff,
      -23 & 0xff,
      -30 & 0xff,
       48 & 0xff,
       89 & 0xff,
       52 & 0xff,
       38 & 0xff,
       98 & 0xff,
       39 & 0xff,
      -95 & 0xff
    )
  

See it on sqlfiddle.