How Can I Implement Custom Sorting in Oracle SQL to Prioritize Specific Values?

Custom Sorting in Oracle SQL

When ordering data in Oracle SQL, there are times when a customized sorting order is necessary, such as prioritizing certain values to appear at the top. One common scenario is prioritizing a specific currency, such as USD, amidst a mix of currencies.

To order a column based on a custom priority, the CASE or DECODE functions can be utilized. Here's how:

Using CASE

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

By assigning numeric values to each currency, the sorting will prioritize USD with a value of 1, followed by BHT (2), JPY (3), and MYR (4). Any other currencies not specified will fall under the default value of 5.

Using DECODE (Oracle-specific)

A more concise syntax can be achieved using DECODE:

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

Alternative for Unmentioned Currencies

If the priority order needs to include currencies not explicitly mentioned in the CASE/DECODE expression, the following modification can be used:

order by 
    CASE 
       when currency = 'USD' then '001' 
       else currency
    END

This assigns a character value to USD ('001'), ensuring its placement at the top, while leaving the remaining currencies to be sorted alphabetically.

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