1. Type in Service.msc in Run Command.
2. Once the Servcies App is opened. Look for MySQL57 Service. And restart it.
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3. Then open MySQL WorkBench and in your database run the following SQL.
Where AjaxSamples is name of my Database.
use AjaxSamples;
set global optimizer_switch='derived_merge=OFF';
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4. Restart the MySQL57 Service again.
5. Now in Visual Studio, Right Click and update the edmx and finally save it.
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Reference: StackOverFlow