MySQL: Frequently asked Interview Questions and Answers Part 3

What is heap table ?

Table without a cluster index is called as Heap Table. Data is stored in the heap without specifying an order.
Initially, data stored in the order of its inserted, but later database engine can move data around in the heap so you cannot predict the order of data and because of this you have to apply ORDER BY clause for each and every use.
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Is MySQL supporting Heap Stroage Engine?

MySQL Memory Storage Engine also called as Heap Storage structure.
Using Memory Storage Engine you can store table of data in server memory for fast retrieval. This table of data also supports B-Tree index so you can get results in the best optimized way. Auto_Increment also supported by the Tables of Memory Engine.
There might be chances of loss data when any  hardware crashes or power outage of Server Memory.
You can store and use only those data which are in temporary use and make sure that data in memory engine has always back up in physical stored table.
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What is difference between Temporary Table and Memory Table ?

Temporary Table is only for running current session. Once running session completed its execution than Temporary Table will be discarded. You cannot use Temporary Table for multiple sessions.
Memory Table can hold data for across all running sessions and connections.
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How you can set the max size of Heap Table?

Using max_heap_table_size this MySQL Config variable.

May I store BLOB into HEAP Table?

No, You can not store BLOG or Text Data.
Auto_Increment is also not supported by HEAP table.

May I connect MySQL with any other RDBMS product like, PostgreSQL.

Yes, You can connect using three different ways ODBC Connection , DSN and Foreign Data Wrapper(FDW).

What is the login command to connect MySQL in Unix?

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

Have you ever used myisamchk command?

Yes, its compress the MyISAM tables by reducing disk and memory usage.

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