Synechron MySQL Interview Questions Answers

Explain Access Control Lists.

An ACL (Access Control List) is a list of permissions that is associated with an object. This list is the basis for MySQL server’s security model and it helps in troubleshooting problems like users not being able to connect.

MySQL keeps the ACLs (also called grant tables) cached in memory. When a user tries to authenticate or run a command, MySQL checks the authentication information and permissions against the ACLs, in a predetermined order.

What are federated tables?

Federated tables which allow access to the tables located on other databases on other servers.

What, if a table has one column defined as TIMESTAMP?

Timestamp field gets the current timestamp whenever the row gets altered.

What happens when the column is set to AUTO INCREMENT and if you reach maximum value in the table?

It stops incrementing. Any further inserts are going to produce an error, since the key has been used already.

Synechron Most Frequently Asked Latest MySQL Interview Questions Answers

How can we find out which auto increment was assigned on Last insert?

LAST_INSERT_ID will return the last value assigned by Auto_increment and it is not required to specify the table name.

How can you see all indexes defined for a table?

Indexes are defined for the table by:

SHOW INDEX FROM <tablename>;

What do you mean by % and _ in the LIKE statement?

% corresponds to 0 or more characters, _ is exactly one character in the LIKE statement.

How can we convert between Unix & MySQL timestamps?

UNIX_TIMESTAMP is the command which converts from MySQL timestamp to Unix timestamp

FROM_UNIXTIME is the command which converts from Unix timestamp to MySQL timestamp.

What are the column comparisons operators?

The = , <>, <=, <, >=, >,<<,>>, <=>, AND, OR, or LIKE operators are used in column comparisons in SELECT statements.

What are the drivers in MySQL?

Following are the drivers available in MySQL:

PHP Driver
JDBC Driver
ODBC Driver
C WRAPPER
PYTHON Driver
PERL Driver
RUBY Driver
CAP11PHP Driver
Ado.net5.mxj

What does a TIMESTAMP do on UPDATE CURRENT_TIMESTAMP data type?

TIMESTAMP column is updated with Zero when the table is created.  UPDATE CURRENT_TIMESTAMP modifier updates the timestamp field to  current time whenever there is a change in other fields of the table.

What is the difference between primary key and candidate key?

Every row of a table is identified uniquely by primary key. There is only one primary key for a table.

Primary Key is also a candidate key. By common convention, candidate key can be designated as primary and which can be used for any foreign key references.

How do you login to MySql using Unix shell?

We can login through this command:

# [mysql dir]/bin/mysql -h hostname -u <UserName> -p <password>

What does myisamchk do?

It compress the MyISAM tables, which reduces their disk or memory usage.

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

Maximum size of Heal table can be controlled by MySQL config variable called max_heap_table_size.

How can we get the number of rows affected by query?

Number of rows can be obtained by

SELECT COUNT (user_id) FROM users;
1
SELECT COUNT (user_id) FROM users;

Is Mysql query is case sensitive?

No.

SELECT VERSION(), CURRENT_DATE;
SeLect version(), current_date;
seleCt vErSiOn(), current_DATE;
1
2
3
SELECT VERSION(), CURRENT_DATE;
SeLect version(), current_date;
seleCt vErSiOn(), current_DATE;


All these examples are same. It is not case sensitive.