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SQL Join

Troubleshooting a SQL Join

Debug common SQL JOIN problems and unexpected results. Learn to troubleshoot missing rows, duplicates, and incorrect JOIN conditions.

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I shot a training video today while I was answering a SQL Join question on Yahoo Answers.

During the video, I construct the database, tables, and example data.

Then I tried to run the current query to see what error I get. Finally, I work through the issue and fix the join.

Here is the video:

If you couldn-t see the question well in the video, here is a reprint.

**Database SQL query issues?

*I have developed the database with the following tables:

**STUDENT

S_ID PRIMARY KEY

S_FNAME

S_LNAME

S_ADDRESS

S_CITY

S_STATE

S_ZIPCODE

S_PHONE


**SCHOLARSHIPS

S_ID PRIMARY KEY FOREIGN KEY REFERENCES STUDENT

SC_MAJOR

SC_ACADEMIC

SC_ATHLETIC ***

GPA

S_ID PRIMARY KEY FOREIGN KEY REFERENCES STUDENT

G_GPA

G_CLASS /(4 is for Seniors)/

I then inputted data and did the following SQL query:

**SELECT S_ID, S_LNAME, S_FNAME, S_ADDRESS, S_CITY, S_STATE, S_ZIPCODE, S_PHONE

FROM STUDENT

WHERE GPA.G_CLASS = 4

ORDER BY S_LNAME, S_FNAME;

**I get the following error:

The data content could not be loaded. Column not found: GPA.G_CLASS.

Please assist with any tutoring or assisting. Thank you.

question/

My answer is to put in the inner join condition.

Here is the final query:

SELECT STUDENT.S_ID, S_LNAME, S_FNAME, S_ADDRESS, S_CITY, S_STATE, S_ZIPCODE, S_PHONE

FROM STUDENT inner join GPA on STUDENT.S_ID=GPA.S_ID

WHERE GPA.G_CLASS = 4

ORDER BY S_LNAME, S_FNAME;

I am attaching the script to create and populate the tables and the Microsoft Excel file so you can see how I create my INSERT statements.

SqlTrainingOnlineUniversityDB.zip

Let me know if you have any questions or comments by posting them below.

About Joey Blue

Joey Blue teaches practical data skills that companies actually use. With 25+ years of experience solving real data problems for Fortune 500 companies, he's helped 152,000+ students learn SQL, Power BI, reporting, and modern analytics—cutting straight to what works.