How to Prioritize USD Currency in Oracle SQL Queries?

Custom Order in Oracle SQL: Prioritizing Currencies

When querying data containing transactions in various currencies, the need often arises to order the results based on a custom preference. In this specific scenario, the requirement is to place the USD currency at the top of the order, followed by the rest of the currencies sorted in ascending order.

Oracle SQL provides several methods for achieving this custom ordering. One approach involves using the CASE expression, which assigns a numerical value or character string to each currency:

order by 
    case 
       when currency = 'USD' then 1 
       when currency = 'BHT' then 2
       when currency = 'JPY' then 3
       when currency = 'MYR' then 4
       else 5
    end

Alternatively, the DECODE function can be employed to perform the same mapping:

order by decode(currency, 'USD', 1, 'BHT', 2, 'JPY', 3, 'MYR', 4, 5)

However, this method relies on explicitly specifying the currencies in the order of precedence, which can become cumbersome if the currency list is extensive or subject to change.

To ensure a consistent ordering regardless of the number or type of currencies in the data, another approach is to convert the currencies to character values and use an alphabetical ordering:

order by 
    case 
       when currency = 'USD' then '001' 
       else currency
    end

Since characters are sorted after numeric digits, this method effectively places USD at the top of the order and sorts the remaining currencies alphabetically.

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