Final answer:
When joining 3 tables in a SELECT statement, 2 join conditions are necessary in the WHERE clause to adequately link the tables and avoid a Cartesian product. The structure and goal of the query may influence the type of join and grouping used.
Step-by-step explanation:
When joining 3 tables in a SELECT statement, typically 2 join conditions are needed in the WHERE clause. This is because each join condition serves to specify how two tables are related. Imagine you have three tables: A, B, and C. You would first join A to B using one condition, and then you must join either A or B to C with a second condition. Without both conditions, there would be a missing link between the tables, potentially leading to a Cartesian product, which means a multiplication of rows that does not represent the correct relational data.
In terms of grouping the data differently, depending on the structure of the tables and the relationships between them, you might use alternative join types (such as LEFT JOIN or FULL OUTER JOIN) or additional SQL clauses like GROUP BY to aggregate data. The benefit of this depends on the specific goal of the query - whether to provide a summation, average, or other grouped result of the data.
Switching between the tables can occur as part of the thought process to ensure that the join conditions properly reflect the logical connections intended by the query's design.