MS SQL Update WHERE value is NULL

This example replaces null with an empty string in SomeTable.SomeColum

UPDATE SomeTable SET SomeColumn = '' WHERE SomeColumn IS NULL

The important thing to note here is that the check to find the value that is NULL is based on “IS NULL” (it is not possible to use the equals sign to check for NULL)

MS SQL SELECT WHERE value is NULL

Here is how to do a select where a column have NULL as the stored value.

SELECT * FROM SomeTable WHERE SomeColumn IS NULL

Equals sign does not work for null, trying to use the equals operator generates the result Unknown (it is not true nor false)

IF i = NULL THEN
      SELECT 'Result is True'
ELSEIF NOT(i = NULL) THEN
      SELECT 'Result is False'
ELSE
      SELECT 'Result is Unknown';
 
--This will end with Result is Unknown

This is based on the fact that null was introduced to represent “missing information and inapplicable information” in the database model and based on that statement using equals null was not implemented.

Arduino ultrasonic sensor (HC-SR04 or HY-SRF05)

Both these ultrasonic range modules are fairly cheap modules, expect the HY-SRF05 to be the more expensive of the these two.

At a quick glance there are only small differences between these two:

  HC-SR04 HY-SRF05
Working Voltage 5 VDC 5 VDC
Static current < 2mA <2 mA
Output signal: Electric frequency signal, high level 5V, low level 0V Electric frequency signal, high level 5V, low level 0V
Sensor angle < 15 degrees < 15 degrees
Detection distance (claimed) 2cm-450cm 2cm-450cm
precision ~3 mm ~2 mm
Input trigger signal 10us TTL impulse 10us TTL impulse
Echo signal output TTL PWL signal output TTL PWL signal
Pins
  1. VCC
  2. trig(T)
  3. echo(R)
  4. GND
  1. VCC
  2. trig(T)
  3. echo(R)
  4. OUT
  5. GND

Not sure what the out pin is about, I have seen claims that it goes high when it detects a obstacle.
From my personal observations the HY-SRF05 seems like a slightly more accurate sensor and seems to have a much better range [I even got it to measure beyond the 4.5 meters it claims] – but if I were to build for instance a robot that should not collide with a wall that would not matter.

In short a ultrasonic sensor like this works like:

  • Send a pulse signal to I/O TRIG which is at least 10us long, this will activate the module to start detecting
  • The ultrasonic module will automatically send eight 40khz square waves, and will automatically detect when there is a reflect signal;
  • When there is an reflect signal back, the ECHO I/O will output a high level, the duration of the high-level signal is the time from untral sonic launch to return. As a result, the Measured distance = (T(Time of High Level output ) * (340M / S)) / 2 The reason for the division by two is that since this is a echo it has traveled both to and from the object. Note the speed of sound is dependent of the temperature so keep that in mind if you need accuracy

And here comes a code sample that works with both of these

/*
Tested with HY-SRF05, HC-SR04
Assuming a room temp of 20 degrees centigrade
The circuit:
	* VVC connection of the sensor attached to +5V
	* GND connection of the sensor attached to ground
	* TRIG connection of the sensor attached to digital pin 12
        * ECHO connection of the sensor attached to digital pin 13
*/
 
const int TRIG_PIN = 12;
const int ECHO_PIN = 13;
 
void setup() {
  // initialize serial communication:
  Serial.begin(9600);
 
  pinMode(TRIG_PIN,OUTPUT);
  pinMode(ECHO_PIN,INPUT);
}
 
void loop()
{
   long duration, distanceCm, distanceIn;
 
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  duration = pulseIn(ECHO_PIN,HIGH);
 
  // convert the time into a distance
  distanceCm = duration / 29.1 / 2 ;
  distanceIn = duration / 74 / 2;
 
  if (distanceCm <= 0){
    Serial.println("Out of range");
  }
  else {
    Serial.print(distanceIn);
    Serial.print("in, ");
    Serial.print(distanceCm);
    Serial.print("cm");
    Serial.println();
  }
  delay(1000);
}

And something that I noticed is very important is the quality of the 5V I got from my USB port when the Arduino was hooked up. At first I got a very noisy signal that was only able to detect ranges of about 10 cm, but after I swapped the connection to not use a usb-hub the results were much better.

And to finish off here comes a bit more about how to calculate the distance based on the time for the sound:

c = 331.3 + 0.606 × Temperature_in_C

so for 20 degrees it would be

c = 331.3 + 0.606 × 20 = 343.42 m/s

And for a lot better explenation, check out wikipedia

Java: Getting the Document from a Node or Element

When we for instance wishes to add a new element we need to pass along the document. If we have a element or a node we can get the document that way. Simply call getOwnerDocument and we are good.

Element element = //code to get a element
Node node = //code to get a node
 
//document from Node
Document document = node.getOwnerDocument();
 
//document from a Element
Document document = element.getOwnerDocument();

Java: Adding a Element under an Element (or Converting a Element to a Node)

When using Document a Element can only be appended with a Node, but what if we have a Element ?

Easy, Element extends Node so just pass the Element along and all is well

import org.w3c.dom.Document;
import org.w3c.dom.Element;
 
Document doc;
Element newElement;
Element oldElement; //code to find that
newElement = doc.createElement("tag");
oldElement.appendChild(newElement);

Java: Creating a enum and converting from a string to the Enum

Here is a simple example of how create a Enum and how to convert from a String to the Enum (the common reason for doing this would be is we at some point have for OurEnum.toString() and now wishes to get back to the OurEnum)

First we need to create the Enum, and this needs to be in its own file

public enum OurEnum { ENUM_A, ENUM_B, ENUM_C }

When we then later on (for instace have saved the toString value in a xml file) wish to

String ourEnumAsAString = "ENUM_A"; //replace with code to read the value
OurEnum ourEnum = OurEnum.valueOf(ourEnumAsAString);

Android resize a bitmap

Here is a snippet to scale down a bitmap – the original bitmap still needs to fit on memory though

InputStream bitmap = mContext.getAssets().open("image.file");
Bitmap scaledBitmap= Bitmap.createScaledBitmap(BitmapFactory.decodeStream(bitmap), 120, 120, false);
bitmap.

Android set background color of ActionBar

Here is a snipet that will set the background color of a ActionBar to a hexcolor.

final ActionBar bar = getActionBar();
 
bar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
bar.setDisplayOptions(0, ActionBar.DISPLAY_SHOW_TITLE);
bar.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#000000")));

Color.parseColor will take any hexstring of a color and make it into a int.

git diff “old mode 100755 new mode 100644”

What git is trying to say here is that the mode of the files have changed, the content of the file is still the same.

If this is common and the filemodes are not important for this project we can simply tell git to ignore this.

Either by telling git to do this as default or only for this project.

Default

git config core.filemode false

Only for this project edit .git/config

[Core]
filemode = false

And in case we do need to check in single filemode changes the following works

git update-index --chmod=(+|-)x path/to/file

Android: Suppressing the warning about using px in layout xml

When working with for instance the Sony SmartWatch there is a need to specify layout for the Watch in pixels (not device pixels) – as the SmartWatch is a fixed size and not dependent of the device it is connected to. When this is done the lint verification will warn about this being a bad idea, but it is possible to suppress this warning by adding the following to the xml file:

  1. add the namespace xmlns:tools=”http://schemas.android.com/tools”
  2. and then then you can disable the px-warnings by including this in your view: tools:ignore=”PxUsage”.

Example:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    android:background="@drawable/background"
>
 
    <View
        tools:ignore="PxUsage"
        android:id="@+id/smartWatchView"
        android:layout_width="128px"
        android:layout_height="128px"
        android:visibility="visible"
        android:layout_centerInParent="true" 
    />
 
</RelativeLayout>