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  3. Introduction to Relational Databases in SQL

Exercise

Populate the "professor_id" column

Now it's time to also populate professors_id. You'll take the ID directly from professors.

Here's a way to update columns of a table based on values in another table: 

UPDATE table_a
SET column_to_update = table_b.column_to_update_from
FROM table_b
WHERE condition1 AND condition2 AND ...;

This query does the following:

  1. For each row in table_a, find the corresponding row in table_b where condition1, condition2, etc., are met.
  2. Set the value of column_to_update to the value of column_to_update_from (from that corresponding row).

The conditions usually compare other columns of both tables, e.g. table_a.some_column = table_b.some_column. Of course, this query only makes sense if there is only one matching row in table_b.

Instructions 1/3

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First, have a look at the current state of affiliations by fetching 10 rows and all columns.