Wednesday, August 26, 2015

25 Best MySQL DATABASE interview questions

How do you start MySQL on Linux?
- /etc/init.d/mysql start

How do you start and stop MySQL on Windows?
net start MySQL, net stop MySQL
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.
 
Have you ever used MySQL Administrator and MySQL Query Browser? Describe the tasks you accomplished with these tools.
 
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.
 
How do you change a password for an existing user via mysqladmin?
mysqladmin -u root -p password "newpassword"
 
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.
 
Explain the difference between mysql and mysqli interfaces in PHP?
mysqli is the object-oriented version of mysql library functions.
 
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 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.
 
Use mysqldump to create a copy of the database?
 mysqldump -h mysqlhost -u username -p mydatabasename > dbdump.sql
 
What happens if a table has one column defined as TIMESTAMP? 
That field gets the current timestamp whenever the row gets altered.
 
But what if you really want to store the timestamp data, such as the publication date of the article? Create two columns of type TIMESTAMP and use the second one for your real data.
 
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.
 
 
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Thursday, August 20, 2015

Bootstrap 4 Alpha

First alpha release of Bootstrap 4. Hell yeah!




There are a ton of major changes to Bootstrap and it’s impossible to cover them all in detail here, so here are some of our favorite highlights:
  • Moved from Less to Sass. Bootstrap now compiles faster than ever thanks to Libsass, and we join an increasingly large community of Sass developers.
  • Improved grid system. We’ve added a new grid tier to better target mobile devices and completely overhauled our semantic mixins.
  • Opt-in flexbox support is here. The future is now—switch a boolean variable and recompile your CSS to take advantage of a flexbox-based grid system and components.
  • Dropped wells, thumbnails, and panels for cards. Cards are a brand new component to Bootstrap, but they’ll feel super familiar as they do nearly everything wells, thumbnails, and panels did, only better.
  • Consolidated all our HTML resets into a new module, Reboot. Reboot steps in where Normalize.css stops, giving you more opinionated resets like box-sizing: border-box, margin tweaks, and more all in a single Sass file.
  • Brand new customization options. Instead of relegating style embellishments like gradients, transitions, shadows, and more to a separate stylesheet like v3, we’ve moved all those options into Sass variables. Want default transitions on everything or to disable rounded corners? Simply update a variable and recompile.
  • Dropped IE8 support and moved to rem and em units. Dropping support for IE8 means we can take advantage of the best parts of CSS without being held back with CSS hacks or fallbacks. Pixels have been swapped for rems and ems where appropriate to make responsive typography and component sizing even easier. If you need IE8 support, keep using Bootstrap 3.
  • Rewrote all our JavaScript plugins. Every plugin has been rewritten in ES6 to take advantage of the newest JavaScript enhancements. They also now come with UMD support, generic teardown methods, option type checking, and tons more.
  • Improved auto-placement of tooltips and popovers thanks to the help of a tool called Tether.
  • Improved documentation. We rewrote it all in Markdown and added a few handy plugins to streamline examples and code snippets to make working with our docs way easier. Improved search is also on it’s way.
  • And tons more! Custom form controls, margin and padding classes, new utility classes, and more have also been included.

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