ORDER BY expressions in SQL

Friendly reminder: when you ORDER BY something in SQL, that something does not necessarily need to be a column, but could be an expression, the output of which can be ordered.

In the example below, we'd like to ORDER by sales decreasingly, but show the 'direct' sales first.

This is achieved by using a CASE WHEN that will rank direct sales above other types of sales, then sorting by the sales decreasingly.

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