Error:
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Database diagram support objects cannot be installed because this
database does not have a valid owner. To continue, first use the Files
page of the Database Properties dialog box or the ALTER AUTHORIZATION
statement to set the database owner to a valid login, then add the
database diagram support objects.
解决方法：
1. 右键点击数据库，选“properties ”
2. 点选左侧“Options”
3. 在'Compatibility Level' 选 'SQL Server 2005(90)'
4. 点选左侧“Files”
5. 在owner里填入 'sa'
6. OK
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说明，主要是owner的问题，不要管它的提示，可能把owner改一下，再改回去，问题就解决了。