Insert a new user, sitecore\Admin
. Then follow the instructions on this question to set the proper password.
For Sitecore 9, you need @Derek Dysart's answer.
SQL for inserting into the Membership database would look something like this:
declare @now datetime
set @now= GETDATE()
exec aspnet_Membership_CreateUser 'sitecore','sitecore\Admin','pass@word1', '','[email protected]','','',1,@now,@now,0,0,null
Source: https://stackoverflow.com/a/19258123/81631
I believe you will still need to update the password and salt as described in the referenced post.
Alternatively, these are the values in a default installation. From the dbo.aspnet_Membership
table.
ApplicationId UserId Password PasswordFormat PasswordSalt MobilePIN Email LoweredEmail PasswordQuestion PasswordAnswer IsApproved IsLockedOut CreateDate LastLoginDate LastPasswordChangedDate LastLockoutDate FailedPasswordAttemptCount FailedPasswordAttemptWindowStart FailedPasswordAnswerAttemptCount FailedPasswordAnswerAttemptWindowStart Comment
DD20E696-45B0-4074-B50E-F34B47F1E454 68FFFAA2-1FFE-4006-B661-A8B6B80C81DE Tm9jY7uSHNQnx08P70kiVEBO2YM= 1 n4n5/iUJKDrabOzQyLOU8Q== NULL NULL NULL 1 0 2017-12-19 15:40:30.000 2018-07-10 16:05:48.587 2017-12-19 15:40:30.000 1754-01-01 00:00:00.000 0 1754-01-01 00:00:00.000 0 1754-01-01 00:00:00.000 Sitecore Administrator