- What is MySQL?
- What are DDL, DML and DCL?
- If the value in the column is repeatable, how do you find out the unique values?
- How do you get the number of rows affected by query?
- How do you find out which auto increment was assigned on the last insert?
- How to change a column from VARCHAR(10) to VARCHAR(50)?
- When do you ORDER BY in DELETE statement?
- How to delete a column?
- How to convert a string to UTF-8?
- How do you concatenate strings in MySQL?
- What is the difference between Unix timestamps and MySQL timestamps?
- How to start MySQL on Linux?
- What is the default port for MySQL Server?
- What are some good ideas regarding user security in MySQL?
- Explain advantages of MyISAM over InnoDB?
- Explain advantages of InnoDB over MyISAM?
- Explain the difference between MyISAM Static and MyISAM Dynamic?
- What are HEAP tables in MySQL?
- Explain the difference between BOOL, TINYINT and BIT?
- How to Make MySQL Secure Against Crackers?
- What are CSV tables?
- How the Privilege System Works in mysql?
- What issues should I be aware of when setting up two-way replication?
- How do I rotate replication logs?
- When and how much can MySQL replication improve the performance of my system?
- How can I use replication to provide redundancy/high availability?
- How MySQL Uses Memory?
- How MySQL Locks Tables?
- How MySQL uses DNS?
- How MySQL Uses Indexes?
- How MySQL Optimizes WHERE Clauses?
- How MySQL Optimizes DISTINCT?
- How MySQL Optimizes LEFT JOIN and RIGHT JOIN?
- How MySQL Optimizes LIMIT?
- What is the difference between mysql_fetch_array and mysql_fetch_object?
- What are the different table present in MYsql?
Showing posts with label mysql interview question and answers. Show all posts
Showing posts with label mysql interview question and answers. Show all posts
MYSQL INTERVIEW QUESTIONS
MYSQL INTERVIEW QUESTIONS
Explain the difference between FLOAT, DOUBLE and REAL.--MYSQL
Explain the difference between FLOAT, DOUBLE and REAL.--MYSQL
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.
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.
Explain the difference between BOOL, TINYINT and BIT.-Mysql
Explain the difference between BOOL, TINYINT and BIT.-Mysql
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.
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.
What is DDL, DML and DCL?
What is DDL, DML and DCL?
If you look at the large variety of SQL commands, they can be divided into three large subgroups. Data Definition Language deals with database schemas and descriptions of how the data should reside in the database, therefore language statements like CREATE TABLE or ALTER TABLE belong to DDL. DML deals with data manipulation, and therefore includes most common SQL statements such SELECT, INSERT, etc. Data Control Language includes commands such as GRANT, and mostly concerns with rights, permissions and other controls of the database system.
If you look at the large variety of SQL commands, they can be divided into three large subgroups. Data Definition Language deals with database schemas and descriptions of how the data should reside in the database, therefore language statements like CREATE TABLE or ALTER TABLE belong to DDL. DML deals with data manipulation, and therefore includes most common SQL statements such SELECT, INSERT, etc. Data Control Language includes commands such as GRANT, and mostly concerns with rights, permissions and other controls of the database system.
MySQL Interview Faqs,My sql interview questions and answers
MySQL Interview questions and answers
What is MySQL ?
MySQL (pronounced "my ess cue el") is an open source relational database management system (RDBMS) that uses Structured Query Language (SQL), the most popular language for adding, accessing, and processing data in a database. Because it is open source, anyone can download MySQL and tailor it to their needs in accordance with the general public license. MySQL is noted mainly for its speed, reliability, and flexibility. ...
What is DDL, DML and DCL ?
If you look at the large variety of SQL commands, they can be divided into three large subgroups. Data Definition Language deals with database schemas and descriptions of how the data should reside in the database, therefore language statements like CREATE TABLE or ALTER TABLE belong to DDL. DML deals with data manipulation, and therefore includes most common SQL statements such SELECT, INSERT, etc. Data Control Language includes commands such as GRANT, and mostly concerns with rights, permissions and other controls of the database system.
How do you get the number of rows affected by query?
SELECT COUNT (user_id) FROM users would only return the number of user_id’s.
If the value in the column is repeatable, how do you find out the unique values?
Use DISTINCT in the query, such as SELECT DISTINCT user_firstname FROM users; You can also ask for a number of distinct values by saying SELECT COUNT (DISTINCT user_firstname) FROM users;
How do you return the a hundred books starting from 25th?
SELECT book_title FROM books LIMIT 25, 100. The first number in LIMIT is the offset, the second is the number.
You wrote a search engine that should retrieve 10 results at a time, but at the same time you’d like to know how many rows there’re total. How do you display that to the user?
SELECT SQL_CALC_FOUND_ROWS page_title FROM web_pages LIMIT 1,10; SELECT FOUND_ROWS(); The second query (not that COUNT() is never used) will tell you how many results there’re total, so you can display a phrase "Found 13,450,600 results, displaying 1-10". Note that FOUND_ROWS does not pay attention to the LIMITs you specified and always returns the total number of rows affected by query.
How would you write a query to select all teams that won either 2, 4, 6 or 8 games?
SELECT team_name FROM teams WHERE team_won IN (2, 4, 6, 8)
How would you select all the users, whose phone number is null?
SELECT user_name FROM users WHERE ISNULL(user_phonenumber);
What does this query mean: SELECT user_name, user_isp FROM users LEFT JOIN isps USING (user_id) ?
It’s equivalent to saying SELECT user_name, user_isp FROM users LEFT JOIN isps WHERE users.user_id=isps.user_id
How do you find out which auto increment was assigned on the last insert?
SELECT LAST_INSERT_ID() will return the last value assigned by the auto_increment function. Note that you don’t have to specify the table name.
What does –i-am-a-dummy flag to do when starting MySQL?
Makes the MySQL engine refuse UPDATE and DELETE commands where the WHERE clause is not present.
On executing the DELETE statement I keep getting the error about foreign key constraint failing. What do I do?
What it means is that so of the data that you’re trying to delete is still alive in another table. Like if you have a table for universities and a table for students, which contains the ID of the university they go to, running a delete on a university table will fail if the students table still contains people enrolled at that university. Proper way to do it would be to delete the offending data first, and then delete the university in question. Quick way would involve running SET foreign_key_checks=0 before the DELETE command, and setting the parameter back to 1 after the DELETE is done. If your foreign key was formulated with ON DELETE CASCADE, the data in dependent tables will be removed automatically.
When would you use ORDER BY in DELETE statement?
When you’re not deleting by row ID. Such as in DELETE FROM techpreparation_com_questions ORDER BY timestamp LIMIT 1. This will delete the most recently posted question in the table techpreparation_com_questions.
How can you see all indexes defined for a table?
SHOW INDEX FROM techpreparation_questions;
How would you change a column from VARCHAR(10) to VARCHAR(50)?
ALTER TABLE techpreparation_questions CHANGE techpreparation_content techpreparation_CONTENT VARCHAR(50).
How would you delete a column?
ALTER TABLE techpreparation_answers DROP answer_user_id.
What is MySQL ?
MySQL (pronounced "my ess cue el") is an open source relational database management system (RDBMS) that uses Structured Query Language (SQL), the most popular language for adding, accessing, and processing data in a database. Because it is open source, anyone can download MySQL and tailor it to their needs in accordance with the general public license. MySQL is noted mainly for its speed, reliability, and flexibility. ...
What is DDL, DML and DCL ?
If you look at the large variety of SQL commands, they can be divided into three large subgroups. Data Definition Language deals with database schemas and descriptions of how the data should reside in the database, therefore language statements like CREATE TABLE or ALTER TABLE belong to DDL. DML deals with data manipulation, and therefore includes most common SQL statements such SELECT, INSERT, etc. Data Control Language includes commands such as GRANT, and mostly concerns with rights, permissions and other controls of the database system.
How do you get the number of rows affected by query?
SELECT COUNT (user_id) FROM users would only return the number of user_id’s.
If the value in the column is repeatable, how do you find out the unique values?
Use DISTINCT in the query, such as SELECT DISTINCT user_firstname FROM users; You can also ask for a number of distinct values by saying SELECT COUNT (DISTINCT user_firstname) FROM users;
How do you return the a hundred books starting from 25th?
SELECT book_title FROM books LIMIT 25, 100. The first number in LIMIT is the offset, the second is the number.
You wrote a search engine that should retrieve 10 results at a time, but at the same time you’d like to know how many rows there’re total. How do you display that to the user?
SELECT SQL_CALC_FOUND_ROWS page_title FROM web_pages LIMIT 1,10; SELECT FOUND_ROWS(); The second query (not that COUNT() is never used) will tell you how many results there’re total, so you can display a phrase "Found 13,450,600 results, displaying 1-10". Note that FOUND_ROWS does not pay attention to the LIMITs you specified and always returns the total number of rows affected by query.
How would you write a query to select all teams that won either 2, 4, 6 or 8 games?
SELECT team_name FROM teams WHERE team_won IN (2, 4, 6, 8)
How would you select all the users, whose phone number is null?
SELECT user_name FROM users WHERE ISNULL(user_phonenumber);
What does this query mean: SELECT user_name, user_isp FROM users LEFT JOIN isps USING (user_id) ?
It’s equivalent to saying SELECT user_name, user_isp FROM users LEFT JOIN isps WHERE users.user_id=isps.user_id
How do you find out which auto increment was assigned on the last insert?
SELECT LAST_INSERT_ID() will return the last value assigned by the auto_increment function. Note that you don’t have to specify the table name.
What does –i-am-a-dummy flag to do when starting MySQL?
Makes the MySQL engine refuse UPDATE and DELETE commands where the WHERE clause is not present.
On executing the DELETE statement I keep getting the error about foreign key constraint failing. What do I do?
What it means is that so of the data that you’re trying to delete is still alive in another table. Like if you have a table for universities and a table for students, which contains the ID of the university they go to, running a delete on a university table will fail if the students table still contains people enrolled at that university. Proper way to do it would be to delete the offending data first, and then delete the university in question. Quick way would involve running SET foreign_key_checks=0 before the DELETE command, and setting the parameter back to 1 after the DELETE is done. If your foreign key was formulated with ON DELETE CASCADE, the data in dependent tables will be removed automatically.
When would you use ORDER BY in DELETE statement?
When you’re not deleting by row ID. Such as in DELETE FROM techpreparation_com_questions ORDER BY timestamp LIMIT 1. This will delete the most recently posted question in the table techpreparation_com_questions.
How can you see all indexes defined for a table?
SHOW INDEX FROM techpreparation_questions;
How would you change a column from VARCHAR(10) to VARCHAR(50)?
ALTER TABLE techpreparation_questions CHANGE techpreparation_content techpreparation_CONTENT VARCHAR(50).
How would you delete a column?
ALTER TABLE techpreparation_answers DROP answer_user_id.
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