Different between primary key and unique key? 

One table may have more than one Unique Key Constraint
columns, but should have only one Primary Key Constraint
column.
 
Unique key allow us NULL values where Primary key not allow us null values. 
 
 

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Reset the auto increment value for a MySQL table

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The following example changes the auto increment value for the table named "applytable" to 100. This means that the next time you insert a record into this table the value of the auto incremental primary key will be 100. If the highest value for the column is already greater than 100 then it will be set to the highest value plus 1. ALTER TABLE mytable AUTO_INCREMENT = 100   The relevent info are highlighted with red circles in the screenshot below.
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WP Migrate DB

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Friends used WP Migrate DB plugin. Which is very easy to migrate your database from one server to another without any loss information. Trust me I have used this plugin in many website. WP Migrate DB exports your database as a MySQL data dump (much like phpMyAdmin), does a find and replace on URLs and file paths, handles serialized data, then allows you to save it to your computer as an SQL file. To complete the migration, you need to use a database management tool (e.g. phpMyAdmin) to import the SQL file to your database, replacing your existing database. It is perfect for developers who need to migrate fresh data from the production site to their local install, or migrate their locally developed site to a staging or production server. Check Link Click Here
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