Fix duplicate DB when login (backend)

[kyudori]

Description

Fixed login error backend part. #209, #213
Created PR again due to incorrect commit.

Fixes #214

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code cleanup/refactoring
• Documentation update
• This change requires a documentation update
• CI system update
• Test Coverage update

How Has This Been Tested?

• frontend

cd frontend
npm install
npm start

• backend

mvn clean install
cd target
java -jar lpvs-*.jar

Test Configuration:

• Java: v11
• LPVS Release: v1.1.0

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[tiokim]

Please add the UNIQUE constraint to the sql file like below.

--- a/src/main/resources/database_dump.sql
+++ b/src/main/resources/database_dump.sql
@@ -168,7 +168,8 @@ CREATE TABLE `member` (
   `name` varchar(255) NOT NULL,
   `nickname` varchar(255) DEFAULT NULL,
   `provider` varchar(10) NOT NULL,
-  `organization` varchar(255) DEFAULT NULL
+  `organization` varchar(255) DEFAULT NULL,
+  UNIQUE KEY `UK7blitxweiw758g32lg3bhavf6` (`email`,`provider`)

[kyudori]

I made a commit reflecting the your request.
Please review it. @tiokim

• Add the UNIQUE constraint.

[tiokim]

LGTM

[o-kopysov]

LGTM