replace all in file from console

The command is:
sed -i 's/oldString/newString/g' fileToBeReplaced.txt

For MAC the behaviour is more restrictive, and wants to specify an backup file this way:
sed -i.bak 's/oldString/newString/g' fileToBeReplaced.txt

In this case, a backup file ("fileToBeReplaced.txt.bak") will be created.

SQL FOREIGN KEY Constraints

CREATE TABLE buildings (
  building_no int(11) NOT NULL AUTO_INCREMENT,
  building_name varchar(255) NOT NULL,
  address varchar(355) NOT NULL,
  PRIMARY KEY (building_no)
) ENGINE=InnoDB;

 
CREATE TABLE rooms (
  room_no int(11) NOT NULL AUTO_INCREMENT,
  room_name varchar(255) NOT NULL,
  building_no int(11) NOT NULL,
  PRIMARY KEY (room_no),
  KEY building_no (building_no),
  CONSTRAINT rooms_ibfk_1
    FOREIGN KEY (building_no)
    REFERENCES buildings (building_no)
    ON DELETE CASCADE
) ENGINE=InnoDB;

SQL triggers

Syntax:

CREATE TRIGGER trigger_name trigger_time trigger_event
ON table_name
FOR EACH ROW
BEGIN
...
END

Dropping trigger:

DROP TRIGGER table_name.trigger_name

Example 1:

CREATE TABLE account (acct_num INT, amount DECIMAL(10,2));

CREATE TRIGGER ins_sum BEFORE INSERT ON account FOR EACH ROW SET @sum = @sum + NEW.amount;

SET @sum = 0;
mysql> INSERT INTO account VALUES(137,14.98),(141,1937.50),(97,-100.00);
mysql> SELECT @sum AS 'Total amount inserted';

Example 2:

CREATE TRIGGER `tutorial`.`before_delete_carts`
    BEFORE DELETE ON `trigger_carts` FOR EACH ROW
    BEGIN
        DELETE FROM trigger_cart_items WHERE OLD.cart_id = cart_id;
    END

Example 3:

CREATE TRIGGER `after_update_cost`
    AFTER UPDATE ON `trigger_items_cost` FOR EACH ROW
    BEGIN
       UPDATE trigger_items
       SET price = (NEW.cost * 1.3)
       WHERE item_id = NEW.item_id;
    END

Important notes on java synchronisation by stack overflow

I had issues with synchronisation with static variable. Volatile do not help me, but the thread below does (:
http://stackoverflow.com/questions/2120248/how-to-synchronize-a-static-variable-among-threads-running-different-instances-o

HTTP GET and POST requests – differences and advantages

GET requests:

• the parameters are put in the URL string;
• there is limitations for URL string length (something as 4000 bytes), so huge data cannot be passed this way;
• the generated page is suitable for search engine optimization;
• not recommended for sending password (and other sensitive data), because it could be seen in the URL and will exists in browser history;
• sending files in GET requests is not possible;

POST requests:

• huge data could be passed this way;
• suitable for sending passwords;
• POST requests are never cached;
• cannot be bookmarked;

XSD vs DTD

Both XSD and DTD are used for defining the structure of XML file.

1. XSD are newer than DTD.
2. XSD allow making more complicated definitions than DTD (and are recommended to use). 
3. XSD files are XML files.
4. In XSD you could put the restriction on the occurrence of the elements. This is done by using attributes minOccurs and maxOccurs.

Some of the features of XSD (that DTD have not) are:

• support of namespaces;
• existence of data types;