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MS SQL Interview Questions Answers

Question 1 : Privileges Provided by MySQL ?

Answer 1 : Information about user privileges is stored in the user, db, host, tables_priv, and columns_priv tables in the mysql database (that is, in the database named mysql). The names used in this manual to refer to the privileges provided by MySQL are shown below, along with the table column name associated with each privilege in the grant tables and the context in which the privilege applies: Privilege Column Context select Select_priv tables insert Insert_priv tables update Update_priv tables delete Delete_priv tables index Index_priv tables alter Alter_priv tables create Create_priv databases, tables, or indexes drop Drop_priv databases or tables grant Grant_priv databases or tables references References_priv databases or tables reload Reload_priv server administration shutdown Shutdown_priv server administration process Process_priv server administration file File_priv file access on server The select, insert, update, and delete privileges allow you to perform operations on rows in existing tables in a database. SELECT statements require the select privilege only if they actually retrieve rows from a table. You can execute certain SELECT statements even without permission to access any of the databases on the server. For example, you could use the mysql client as a simple calculator: mysql> SELECT 1+1; mysql> SELECT PI()*2; The index privilege allows you to create or drop (remove) indexes. The alter privilege allows you to use ALTER TABLE. The create and drop privileges allow you to create new databases and tables, or to drop (remove) existing databases and tables. Note that if you grant the drop privilege for the mysql database to a user, that user can drop the database in which the MySQL access privileges are stored! The grant privilege allows you to give to other users those privileges you yourself possess. The file privilege gives you permission to read and write files on the server using the LOAD DATA INFILE and SELECT ... INTO OUTFILE statements. Any user to whom this privilege is

Question 2 : But what if you really want to store the timestamp data, such as the publication date of the article?

Answer 2 : Create two columns of type TIMESTAMP and use the second one for your real data.

Question 3 : What the Privilege System Does?

Answer 3 : The primary function of the MySQL privilege system is to authenticate a user connecting from a given host, and to associate that user with privileges on a database such as select, insert, update and delete. Additional functionality includes the ability to have an anonymous user and to grant privileges for MySQL-specific functions such as LOAD DATA INFILE and administrative operations. MySQL User Names and Passwords There are several distinctions between the way user names and passwords are used by MySQL and the way they are used by Unix or Windows: User names, as used by MySQL for authentication purposes, have nothing to do with Unix user names (login names) or Windows user names. Most MySQL clients by default try to log in using the current Unix user name as the MySQL user name, but that is for convenience only. Client programs allow a different name to be specified with the -u or --user options. This means that you can't make a database secure in any way unless all MySQL user names have passwords. Anyone may attempt to connect to the server using any name, and they will succeed if they specify any name that doesn't have a password. MySQL user names can be up to 16 characters long; Unix user names typically are limited to 8 characters. MySQL passwords have nothing to do with Unix passwords. There is no necessary connection between the password you use to log in to a Unix machine and the password you use to access a database on that machine. MySQL encrypts passwords using a different algorithm than the one used during the Unix login process. Note that even if the password is stored 'scrambled', and knowing your 'scrambled' password is enough to be able to connect to the MySQL server! Connecting to the MySQL Server MySQL client programs generally require that you specify connection parameters when you want to access a MySQL server: the host you want to connect to, your user name, and your password. For example, the mysql client can be started like this (optional arguments are enclosed between `[' and `]'): shell> mysql [-h host_name] [-u user_name] [-pyour_pass] Alternate forms of the -h, -u, and -p options are --host=host_name, --user=user_name, and --password=your_pass. Note that there is no space between -p or --password= and the password following

Question 4 : How to Cope Without COMMIT/ROLLBACK

Answer 4 : The following mostly applies only for ISAM, MyISAM, and HEAP tables. If you only use transaction-safe tables (BDB tables) in an a update, you can do COMMIT and ROLLBACK also with MySQL. The problem with handling COMMIT-ROLLBACK efficiently with the above table types would require a completely different table layout than MySQL uses today. The table type would also need extra threads that do automatic cleanups on the tables, and the disk usage would be much higher. This would make these table types about 2-4 times slower than they are today. For the moment, we prefer implementing the SQL server language (something like stored procedures). With this you would very seldom really need COMMIT-ROLLBACK. This would also give much better performance. Loops that need transactions normally can be coded with the help of LOCK TABLES, and you don't need cursors when you can update records on the fly. We at TcX had a greater need for a real fast database than a 100% general database. Whenever we find a way to implement these features without any speed loss, we will probably do it. For the moment, there are many more important things to do. Check the TODO for how we prioritize things at the moment. (Customers with higher levels of support can alter this, so things may be reprioritized.) The current problem is actually ROLLBACK. Without ROLLBACK, you can do any kind of COMMIT action with LOCK TABLES. To support ROLLBACK with the above table types, MySQL would have to be changed to store all old records that were updated and revert everything back to the starting point if ROLLBACK was issued. For simple cases, this isn't that hard to do (the current isamlog could be used for this purpose), but it would be much more difficult to implement ROLLBACK for ALTER/DROP/CREATE TABLE. To avoid using ROLLBACK, you can use the following strategy: Use LOCK TABLES ... to lock all the tables you want to access. Test conditions. Update if everything is okay. Use UNLOCK TABLES to release your locks. This is usually a much faster method than using transactions with possible ROLLBACKs, although not always. The only situation this solution doesn't handle is when someone kills the threads in the middle of an update. In this case, all locks will be released but some of the updates may not have been executed. You can also use functions to update records in a

Question 5 : Causes of Access denied Errors?

Answer 5 : If you encounter Access denied errors when you try to connect to the MySQL server, the list below indicates some courses of action you can take to correct the problem: The server should let you connect without error. You should also make sure you have a file `user.MYD' in the MySQL database directory. Ordinarily, this is `PATH/var/mysql/user.MYD', where PATH is the pathname to the MySQL installation root. After a fresh installation, you should connect to the server and set up your users and their access permissions: shell> mysql -u root mysql The server should let you connect because the MySQL root user has no password initially. That is also a security risk, so setting the root password is something you should do while you're setting up your other MySQL users. If you try to connect as root and get this error: Access denied for user: '@unknown' to database mysql this means that you don't have an entry in the user table with a User column value of 'root' and that mysqld cannot resolve the hostname for your client. In this case, you must restart the server with the --skip-grant-tables option and edit your `/etc/hosts' or `\windows\hosts' file to add an entry for your host. If you updated an existing MySQL installation from a version earlier than Version 3.22.11 to Version 3.22.11 or later, did you run the mysql_fix_privilege_tables script? If not, do so. The structure of the grant tables changed with MySQL Version 3.22.11 when the GRANT statement became functional. If you can't get your password to work, remember that you must use the PASSWORD() function if you set the password with the INSERT, UPDATE, or SET PASSWORD statements. The PASSWORD() function is unnecessary if you specify the password using the GRANT ... INDENTIFIED BY statement or the mysqladmin password command. localhost is a synonym for your local hostname, and is also the default host to which clients try to connect if you specify no host explicitly. However, connections to localhost do not work if you are running on a system that uses MIT-pthreads (localhost connections are made using Unix sockets, which are not supported by MIT-pthreads). To avoid this problem on such systems, you should use the --host option to name the server host explicitly. This will make a TCP/IP connection to the mysqld serve

Question 6 : How do you control the max size of a HEAP table?

Answer 6 : MySQL config variable max_heap_table_size.

Question 7 : How would you delete a column?

Answer 7 : ALTER TABLE techpreparation_answers DROP answer_user_id.

Question 8 : How do you get a portion of a string?

Answer 8 : SELECT SUBSTR(title, 1, 10) from techpreparation_questions;

Question 9 : When you create a new Message Type in the SQL Server 2005 Service Broker, what does the Authorization parameter signify?

Answer 9 : The owner of the message type. This parameter determines the owner of the message type. This defaults to the current user.

Question 10 : What is the recommended way to send mail from SQLAgent in SQL Server 2005?

Answer 10 : Database Mail You can use either Database Mail or SQLMail with SQL Agent in SQL Server 2005. However since SQLMail will be removed, it is recommended that you use Database Mail.

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