MySQL Interview Questions

• How do you start MySQL on Linux? - /etc/init.d/mysql start
• Explain the difference between mysql and mysqli interfaces in PHP? - mysqli is the object-oriented version of mysql library functions.
• What’s the default port for MySQL Server? - 3306
• What does tee command do in MySQL? - tee followed by a filename turns on MySQL logging to a specified file. It can be stopped by command notee.
• Can you save your connection settings to a conf file? - Yes, and name it ~/.my.conf. You might want to change the permissions on the file to 600, so that it’s not readable by others.

How do you change a password for an existing user via mysqladmin? - mysqladmin -u root -p password "newpassword"

What are some good ideas regarding user security in MySQL? - There is no user without a password. There is no user without a user name. There is no user whose Host column contains % (which here indicates that the user can log in from anywhere in the network or the Internet). There are as few users as possible (in the ideal case only root) who have unrestricted access.

Explain the difference between MyISAM Static and MyISAM Dynamic. - In MyISAM static all the fields have fixed width. The Dynamic MyISAM table would include fields such as TEXT, BLOB, etc. to accommodate the data types with various lengths. MyISAM Static would be easier to restore in case of corruption, since even though you might lose some data, you know exactly where to look for the beginning of the next record.

• What does myisamchk do? - It compressed the MyISAM tables, which reduces their disk usage.
• Explain advantages of InnoDB over MyISAM? - Row-level locking, transactions, foreign key constraints and crash recovery.
• Explain advantages of MyISAM over InnoDB? - Much more conservative approach to disk space management - each MyISAM table is stored in a separate file, which could be compressed then with myisamchk if needed. With InnoDB the tables are stored in tablespace, and not much further optimization is possible. All data except for TEXT and BLOB can occupy 8,000 bytes at most. No full text indexing is available for InnoDB. TRhe COUNT(*)s execute slower than in MyISAM due to tablespace complexity.

• What are HEAP tables in MySQL? - HEAP tables are in-memory. They are usually used for high-speed temporary storage. No TEXT or BLOB fields are allowed within HEAP tables. You can only use the comparison operators = and <=>. HEAP tables do not support AUTO_INCREMENT. Indexes must be NOT NULL.
• How do you control the max size of a HEAP table? - MySQL config variable max_heap_table_size.
• What are CSV tables? - Those are the special tables, data for which is saved into comma-separated values files. They cannot be indexed.
• Explain federated tables. - Introduced in MySQL 5.0, federated tables allow access to the tables located on other databases on other servers.
• What is SERIAL data type in MySQL? - BIGINT NOT NULL PRIMARY KEY AUTO_INCREMENT

• What happens when the column is set to AUTO INCREMENT and you reach the maximum value for that table? - It stops incrementing. It does not overflow to 0 to prevent data losses, but further inserts are going to produce an error, since the key has been used already.
• Explain the difference between BOOL, TINYINT and BIT. - Prior to MySQL 5.0.3: those are all synonyms. After MySQL 5.0.3: BIT data type can store 8 bytes of data and should be used for binary data.
• Explain the difference between FLOAT, DOUBLE and REAL. - FLOATs store floating point numbers with 8 place accuracy and take up 4 bytes. DOUBLEs store floating point numbers with 16 place accuracy and take up 8 bytes. REAL is a synonym of FLOAT for now.

• If you specify the data type as DECIMAL (5,2), what’s the range of values that can go in this table? - 999.99 to -99.99. Note that with the negative number the minus sign is considered one of the digits.
• What happens if a table has one column defined as TIMESTAMP? - That field gets the current timestamp whenever the row gets altered.

If I created a column with data type VARCHAR(3), what would I expect to see in MySQL table? - CHAR(3), since MySQL automatically adjusted the data type.

Draw the architecture of Zend engine?

A:17

The Zend Engine is the internal compiler and runtime engine used by PHP4. Developed by Zeev Suraski and Andi Gutmans, the Zend Engine is an abbreviation of their names. In the early days of PHP4, it worked as follows: The PHP script was loaded by the Zend Engine and compiled into Zend opcode. Opcodes, short for operation codes, are low level binary instructions. Then the opcode was executed and the HTML generated sent to the client. The opcode was flushed from memory after execution.Today, there are a multitude of products and techniques to help you speed up this process. In the following diagram, we show the how modern PHP scripts work; all the shaded boxes are optional. PHP Scripts are loaded into memory and compiled into Zend opcodes.