Under what circumstances should a where clause be added?

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A where clause should be added to a SQL query when you want to filter the results based on certain criteria. The where clause is used to specify the conditions that must be met in order for the rows to be included in the result set. Examples of when a where clause could be added include:

1. Selecting all rows where a specific column equals a certain value
2. Filtering rows based on a range of values
3. Filtering rows based on multiple criteria using logical operators (AND, OR)
4. Excluding rows that meet certain conditions using the NOT operator
5. Joining multiple tables and filtering the results based on conditions in each table.