When order by is null in Oracle

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The default null value sorted by order by in Oracle is the largest, which is placed before all data.
 
However, in most cases, we want the null value to sink to the end. In this case, Oracle provides an extended sort Syntax: nulls first or nulls last
 
Nulls first and nulls last are syntaxes supported by Oracle order.
If the expression nulls first is specified in order by, the null value of the record is ranked first (whether ASC or DESC)

If the expression nulls last is specified in order by, the records with null values will be placed at the end (whether ASC or DESC)
The syntax is as follows:
-- Always put nulls at the beginning

Select * from Dual order by name nulls first

-- Always put nulls at the end

Select * from Dual order by name DESC nulls last