Moving WordPress on localhost?

Hi, i created a website example.com and uses multisite all is working nice but i want to copy it to localhost..i exported database from example.com and imported in localhost (after changing urls from example.com to localhost/web/)
and after altering wp-config.php file.But it shows Error establishing a database connection
Explanation:
To verfiy that the exported sql file of example.com is ok ..i imported it to live website example.com ..it works..similarly i make fresh installation on localhost and exported dtatbase to sql file and then imported it again on localhost it is working..What is the the problem ..i have searched a lot but didn’t find anything useful to solve this issue please help me..!