Hey Karl,
   Thanks for your kind information.
BTW i fixed it. But the import and export options in phpmyadmin has showing an error. It is a common problem for most of the users. (Based on a search in stackoverflow).
I attached a screenshot with this mail. Please kindly have a look. 
If able please tell the procedure to solve this error.



Thank You so much !

> On 23-Jan-2019, at 3:00 PM, Karl Stenerud <email address hidden> wrote:
> 
> Hi,
> 
> Your /var/log/mysql/error.log has the following: [ERROR] [FATAL] InnoDB:
> Table flags are 0 in the data dictionary but the flags in file ./ibdata1
> are 0x4000!
> 
> Are you attempting to open a mysql 8 database with mysql 5? I don't
> think that's supported. Make sure all traces of mysql 8 are removed
> (including databases) before installing mysql 5.
> 
> I'm marking this as invalid for now, but if this error really is caused
> during normal operation of mysql 5 without interference from an old
> mysql 8, please let us know and reopen the ticket. In such a case you
> should probably also check on the mysql bug tracker
> https://bugs.mysql.com/
> 
> 
> Full error message:
> 
> 2019-01-22T06:54:17.395378Z 0 [ERROR] [FATAL] InnoDB: Table flags are 0 in the data dictionary but the flags in file ./ibdata1 are 0x4000!
> 2019-01-22 12:24:17 0x7ff02a461740  InnoDB: Assertion failure in thread 140669478115136 in file ut0ut.cc line 942
> InnoDB: We intentionally generate a memory trap.
> InnoDB: Submit a detailed bug report to http://bugs.mysql.com.
> InnoDB: If you get repeated assertion failures or crashes, even
> InnoDB: immediately after the mysqld startup, there may be
> InnoDB: corruption in the InnoDB tablespace. Please refer to
> InnoDB: http://dev.mysql.com/doc/refman/5.7/en/forcing-innodb-recovery.html
> InnoDB: about forcing recovery.
> 06:54:17 UTC - mysqld got signal 6 ;
> This could be because you hit a bug. It is also possible that this binary
> or one of the libraries it was linked against is corrupt, improperly built,
> or misconfigured. This error can also be caused by malfunctioning hardware.
> Attempting to collect some information that could help diagnose the problem.
> As this is a crash and something is definitely wrong, the information
> collection process might fail.
> 
> key_buffer_size=16777216
> read_buffer_size=131072
> max_used_connections=0
> max_threads=151
> thread_count=0
> connection_count=0
> It is possible that mysqld could use up to 
> key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 76387 K  bytes of memory
> Hope that's ok; if not, decrease some variables in the equation.
> 
> Thread pointer: 0x0
> Attempting backtrace. You can use the following information to find out
> where mysqld died. If you see no messages after this, something went
> terribly wrong...
> stack_bottom = 0 thread_stack 0x30000
> /usr/sbin/mysqld(my_print_stacktrace+0x3b)[0xebde1b]
> /usr/sbin/mysqld(handle_fatal_signal+0x48b)[0x790bbb]
> /lib/x86_64-linux-gnu/libpthread.so.0(+0x12890)[0x7ff028fbf890]
> /lib/x86_64-linux-gnu/libc.so.6(gsignal+0xc7)[0x7ff0282bbe97]
> /lib/x86_64-linux-gnu/libc.so.6(abort+0x141)[0x7ff0282bd801]
> /usr/sbin/mysqld[0x7675ca]
> /usr/sbin/mysqld(_ZN2ib5fatalD1Ev+0x66)[0x1094aa6]
> /usr/sbin/mysqld[0x11426ec]
> /usr/sbin/mysqld[0x1142c6d]
> /usr/sbin/mysqld(_Z6fil_ioRK9IORequestbRK9page_id_tRK11page_size_tmmPvS8_+0x322)[0x114d6d2]
> /usr/sbin/mysqld(_Z13buf_read_pageRK9page_id_tRK11page_size_t+0xdd)[0x11007fd]
> /usr/sbin/mysqld(_Z16buf_page_get_genRK9page_id_tRK11page_size_tmP11buf_block_tmPKcmP5mtr_tb+0x4e5)[0x10d2555]
> /usr/sbin/mysqld(_Z31trx_rseg_get_n_undo_tablespacesPm+0x14f)[0x1072dbf]
> /usr/sbin/mysqld[0x103a218]
> /usr/sbin/mysqld(_Z34innobase_start_or_create_for_mysqlv+0x2de6)[0x103e546]
> /usr/sbin/mysqld[0xf05cc8]
> /usr/sbin/mysqld(_Z24ha_initialize_handlertonP13st_plugin_int+0x4f)[0x7de31f]
> /usr/sbin/mysqld[0xc99ce5]
> /usr/sbin/mysqld(_Z40plugin_register_builtin_and_init_core_sePiPPc+0x1e5)[0xc9d1f5]
> /usr/sbin/mysqld[0x788e70]
> /usr/sbin/mysqld(_Z11mysqld_mainiPPc+0x785)[0x78a585]
> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0x7ff02829eb97]
> /usr/sbin/mysqld(_start+0x2a)[0x780c1a]
> The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
> information that should help you find out what is causing the crash.
> 
> ** Changed in: mysql-5.7 (Ubuntu)
>       Status: New => Invalid
> 
> -- 
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1812798
> 
> Title:
>  package mysql-server-5.7 5.7.24-0ubuntu0.18.04.1 failed to
>  install/upgrade: installed mysql-server-5.7 package post-installation
>  script subprocess returned error exit status 1
> 
> Status in mysql-5.7 package in Ubuntu:
>  Invalid
> 
> Bug description:
>  i have added Mysql APT repo
>  then installed mysql v8.xx
>  then my phpmyadmin stoped working.
>  so i uninstalled mysql-server also purge the apt repo.
>  then i try to install the native mysql-server comes with ubuntu repo
>  so this error came..
> 
>  ProblemType: Package
>  DistroRelease: Ubuntu 18.04
>  Package: mysql-server-5.7 5.7.24-0ubuntu0.18.04.1
>  ProcVersionSignature: Ubuntu 4.15.0-43.46-generic 4.15.18
>  Uname: Linux 4.15.0-43-generic x86_64
>  ApportVersion: 2.20.9-0ubuntu7.2
>  Architecture: amd64
>  Date: Tue Jan 22 12:24:17 2019
>  ErrorMessage: installed mysql-server-5.7 package post-installation script subprocess returned error exit status 1
>  InstallationDate: Installed on 2019-01-02 (19 days ago)
>  InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
>  Logs.var.log.daemon.log:
> 
>  MySQLConf.etc.mysql.conf.d.mysql.cnf: [mysql]
>  MySQLConf.etc.mysql.conf.d.mysqldump.cnf:
>   [mysqldump]
>   quick
>   quote-names
>   max_allowed_packet    = 16M
>  MySQLConf.etc.mysql.mysql.conf.d.mysqld_safe_syslog.cnf:
>   [mysqld_safe]
>   syslog
>  MySQLVarLibDirListing: ['server-key.pem', 'ca-key.pem', 'binlog.000003', 'auto.cnf', 'client-key.pem', 'public_key.pem', 'mysql_upgrade_info', 'private_key.pem', '#innodb_temp', 'debian-5.7.flag', 'ib_logfile1', 'mysql', 'performance_schema', 'binlog.000001', 'binlog.index', 'client-cert.pem', 'server-cert.pem', 'sys', 'ib_buffer_pool', 'ibdata1', 'mysql.ibd', 'phpmyadmin', 'binlog.000002', 'ib_logfile0', 'undo_002', 'ca.pem', 'undo_001']
>  ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.15.0-43-generic root=UUID=95a999aa-99e3-401b-954b-84871a4a1fc0 ro quiet splash vt.handoff=1
>  Python3Details: /usr/bin/python3.6, Python 3.6.7, python3-minimal, 3.6.7-1~18.04
>  PythonDetails: /usr/bin/python2.7, Python 2.7.15rc1, python-minimal, 2.7.15~rc1-1
>  RelatedPackageVersions:
>   dpkg 1.19.0.5ubuntu2
>   apt  1.6.3ubuntu0.1
>  SourcePackage: mysql-5.7
>  Title: package mysql-server-5.7 5.7.24-0ubuntu0.18.04.1 failed to install/upgrade: installed mysql-server-5.7 package post-installation script subprocess returned error exit status 1
>  UpgradeStatus: No upgrade log present (probably fresh install)
> 
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu/+source/mysql-5.7/+bug/1812798/+subscriptions