The operator to concatenate in SQL Server is '+', but this operator is also used to add values.

Being the same operator for both, the query analyzer makes a concatenation or a sum based on the type of data fields being treated. If the fields are of 'string' type, the operator concatenate, and if it has numeric fields, two integers, for example, it add the two values.

A very powerful way to do a table's update in a SQL Server database is to link it with another table with a join, and updating the fields of everyone of its registers using the field's values of the registers linked with the another one. This technique had been discussed in the forum post Update with join or update from select in SQL Server..

The Clouds Economy is a book presenting the multi-dimensional perspective of Cloud Computing (CC): economic, technological and sociological. The publication explains what and for whom CC is, how and why one should take advantage of Cloud solutions. In addition, the book contains the description of the CC evolution from distant yesterday, through deep today, to distant tomorrow. 

To import and export data from SQL Server,  Microsoft provides the tool bpc, which operates by command line. Although it would be appreciated if SQL Server Management Studio would provide some

In order to access to the same database where are you working outside the database server you must activate the service called listener, it has to be listening.

It can happens that the database is properly raised and can not connect from other servers, which are also set correctly (correct TNSNAMES, etc.).. 

In these cases could be that the listener has a problem, or simply has not been initiated.

To Check the status, start or stop it is very simple. Just open a command line session (console terminal, etc..) with the user that has installed the database, and run the lsnrctl command with the following parameters:

• Check your state:
    > lsnrctl status

• Stop the listener:
    > lsnrctl stop

• Start the listener:
    > lsnrctl start

Keep in mind that when you stop the listener, the connections that are already in the database won't be closed, so a short stop is not very traumatic, only connections trying to enter while the listener is stopped are rejected, should not affect anyone who already has an opened session.

If you have the system user who installed the database you can enter SQL Plus as DBA user, without entering a password as follows:

1. Enters the system with this user. 
2. From the command line, go into SQLPlus typing:

> sqlplus "/as sysdba"

If you need to enter using this way because you forgot the password of a user, you can easily change it: 

SQL> alter user user_name identified by new_password;

It can be more than one Database installed on the server, so you have to validate that the environment variables of the Oracle's user are pointing to your database.

For verifying that you has login into the correct database you can execute this statement: 

SQL> select name from v$database; 

Suppose we want to update in our ORACLE database the costs fields of the fact table FAC_TABLE with the unit cost of our table COSTS.

We can do this in two ways:

1. (Slow, but valid for a few data or to sporadic uses)

update FAC_TABLE ft  set UNIT_COST = (select distinct UNIT_COST from COSTS ct  where (ft.id_article = ct.id_article);

2. (The best way is this, and the performance is ideal if you have constraints)

UPDATE ( SELECT ft.UNIT_COST AS old_cost,  ct.UNIT_COST AS new_cost FROM FAC_TABLE ft  INNER JOIN COSTS ct ON ft.id_article ct = ct.id_article) )  SET old_cost = new_cost;

To the proper functionality of this second option you need a UNIQUE or PRIMARY KEY constraint on ct.id_articulo. 
If you don't have this constraint, you can use the hint / * + BYPASS_UJVC * / after the word UPDATE (Bypass update join view constraint).

The performance increase if we have the constraint but even without it, the second option should run quite faster than the first option.

The easiest way to access from an Oracle database objects from another Oracle database is using a DBLINK (being the easiest does not mean that it is always the most desirable, the abuse of DBLINKS can create many problems, both of performance and safety)

To do this it's necessary a user with CREATE DATABASE LINK privilege, and create a DBLINK in the source database (A) by a simple statement such as:

'LNK_from_A_to_B' is the name of the link, 'USER' and 'PASSWORD' are the IDs of the user who will use the link to connect, which will inherit the permissions of all access through the link, and B is the name of the database's instance.

Using the DBLINK we can connect to the objects with the remote database's permissions that user has been provided in the creation statement.

To reference an object from the remote database should indicate the name of the object, concatenated with the character '@' and the name that we had given to the DBLINK.

Example: 

The operation of databases from different manufacturers is similar, but there are many differences between them, even at level of SQL syntax.

For example, if you knows Oracle, and one day you have to do a date conversion with MySQL, you will wonder the following:

- How to do a TO_DATE () / TO_CHAR () with MySQL? 

I open this blog entry to discuss different ways of doing things with each database type. 

Here I link the SQL Tips Bristle Software , which explains quite well how to do some things with MySQL, Oracle and SQL Server, and I find especially useful the chapter on differences between Oracle and SQL Server