Question

When must column names be prefixed by table names in join syntax?

a.When the more than two tables participate in the join
b.Never
c.When the same column name appears in more than one table of the query
d.Only when query speed and database performance is a concern

Answer 1

Column names need to be prefixed by table names during a join when the same column name appears in more than one table to avoid ambiguity, such as when two tables each have a 'id' column.

Step-by-step explanation:

Column names must be prefixed by table names in join syntax when the same column name appears in more than one table of the query. This is necessary to avoid ambiguity. For example, if a query involves joining two tables that both contain a column named 'id', you would need to specify whether you mean table1.id or table2.id when referencing the 'id' column. This helps the database understand which column you're referring to and ensures that the proper data is selected from each table.

Answering the questions provided as a reference:

1. Neither of the tables is more correct; using table names is a matter of necessity to resolve ambiguity, not a matter of correctness.
2. Grouping the data differently generally refers to organizing the data in a way that might be more meaningful or efficient for certain operations; however, in the context of joining tables, the focus is on ensuring clarity by using table names with column names.
3. One might switch between tables when referring to different columns to clearly indicate the source of each piece of data in the query.