如何将Junction表链接到主表

Question

I have a SQL database with the main table called Results. This table stores a record of results of tests that are run nightly.

The Results table has many fields but for arguments say lets just say for now it looks like this:

• ResultID (Unique key field generated upon insert)
• Result (nvchar10)

What I wanted to be able to record was a list of tags used in the tests that were run. The tags may be different for each result and an array of them are stored.

I created a junction table as shown below called Tags:

• TagID (int key field unique generated at runtime)
• ResultID (int)
• ScenarioTag (nvchar128)
• FeatureTag (nvchar128)

So what im looking to do is to link these 2 together. I'm not so great with databases ill be honest.

I was thinking that when I save the test results with my normal SQL query immediately after I would loop through each tag and save the tags to this new table but maybe i'm wrong here?

Psuedocode:

//Returned from previous SQL statement that inserted results values into the DB
int ResultID = SQLQueryReturnValue;

Foreach TAG in TAGS
{
    string SQLQuery = "INSERT INTO TAGS (ResultID, ScenarioTag, FeatureTag)(@ResultID, @ScenarioTag, @FeatureTag)";
    CmdSql.Parameters.AddWithValue("@ResultID", ResultID);
    CmdSql.Parameters.AddWithValue("@ScenarioTag", TAG.Scenario);
    CmdSql.Parameters.AddWithValue("@FeatureTag", TAG.Feature);
    CmdSql.CommandText = SQLQuery;
    CmdSql.Execute();
}

Heres an example of what each table might actually look like:

Results Table
|ResultID | Result |
| 10032   | Pass   |
| 10031   | Fail   |
| 10030   | Fail   |

Tags Table
| TagID | ResultID | ScenarioTag   | FeatureTag |
| 6     | 10032    | Cheque        | Trading    |
| 5     | 10032    | GBP           | Sales      |
| 4     | 10031    | Direct Credit | Trading    |
| 3     | 10031    | GBP           | Purchase   |
| 2     | 10030    | Wire          | Dividends  |
| 1     | 10030    | USD           | Payments   |

So finally onto my question...Is there a way that I can physically link this new "Tags" table to my results table. Its informally linked in a way using the ResultID but theres no physical link.

Answer 1

Is it this you're looking for? (Assumption: This query is looking from results. They do not necessarily have to have Tags...)

SELECT *
FROM Results
LEFT JOIN Tags ON Results.ResultID=Tags.ResultID

EDIT: Maybe I did not understand, what you mean by "physically". You could add a foreign key constraint:

ALTER TABLE Tags ADD CONSTRAINT FK_Tags_Results FOREIGN KEY (ResultID) REFERENCES Results(ResultID);  

This constraint adds a relation to these tables, making sure, that only values existing in Results are allowed in Tags as "ResultID". On the other hand you cannot delete a Result row with existing children in Tags...

If you do this you could alter the top query to:

SELECT *
FROM Tags
INNER JOIN Results ON Results.ResultID=Tags.ResultID

Now you are looking from Tags (leading table) and you know, that each tag must have a ResultID (INNER JOIN).