spark-instrumented-optimizer/docs/sql-ref-syntax-qry-select-orderby.md

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The ORDER BY clause is used to return the result rows in a sorted manner in the user specified order. Unlike the SORT BY clause, this clause guarantees a total order in the output.

Syntax

{% highlight sql %} ORDER BY { expression [ sort_direction | nulls_sort_oder ] [ , ... ] } {% endhighlight %}

Parameters

ORDER BY

Specifies a comma-separated list of expressions along with optional parameters sort_direction and nulls_sort_order which are used to sort the rows.

sort_direction

Optionally specifies whether to sort the rows in ascending or descending order. The valid values for the sort direction are ASC for ascending and DESC for descending. If sort direction is not explicitly specified, then by default rows are sorted ascending.

Syntax: [ ASC | DESC ]

nulls_sort_order

Optionally specifies whether NULL values are returned before/after non-NULL values, based on the sort direction. In Spark, NULL values are considered to be lower than any non-NULL values by default. Therefore the ordering of NULL values depend on the sort direction. If null_sort_order is not specified, then NULLs sort first if sort order is ASC and NULLS sort last if sort order is DESC.

1. If NULLS FIRST (the default) is specified, then NULL values are returned first regardless of the sort order.
2. If NULLS LAST is specified, then NULL values are returned last regardless of the sort order.

Syntax: [ NULLS { FIRST | LAST } ]

Examples

{% highlight sql %} CREATE TABLE person (id INT, name STRING, age INT); INSERT INTO person VALUES (100, 'John', 30), (200, 'Mary', NULL), (300, 'Mike', 80), (400, 'Jerry', NULL), (500, 'Dan', 50);

-- Sort rows by age. By default rows are sorted in ascending manner. SELECT name, age FROM person ORDER BY age;

+-----+----+ |name |age | +-----+----+ |Jerry|null| |Mary |null| |John |30 | |Dan |50 | |Mike |80 | +-----+----+

-- Sort rows in ascending manner keeping null values to be last. SELECT name, age FROM person ORDER BY age NULLS LAST;

+-----+----+ |name |age | +-----+----+ |John |30 | |Dan |50 | |Mike |80 | |Mary |null| |Jerry|null| +-----+----+

-- Sort rows by age in descending manner. SELECT name, age FROM person ORDER BY age DESC;

+-----+----+ |name |age | +-----+----+ |Mike |80 | |Dan |50 | |John |30 | |Jerry|null| |Mary |null| +-----+----+

-- Sort rows in ascending manner keeping null values to be first. SELECT name, age FROM person ORDER BY age DESC NULLS FIRST;

+-----+----+ |name |age | +-----+----+ |Jerry|null| |Mary |null| |Mike |80 | |Dan |50 | |John |30 | +-----+----+

-- Sort rows based on more than one column with each column having different -- sort direction. SELECT * FROM person ORDER BY name ASC, age DESC;

+---+-----+----+ |id |name |age | +---+-----+----+ |500|Dan |50 | |400|Jerry|null| |100|John |30 | |200|Mary |null| |300|Mike |80 | +---+-----+----+ {% endhighlight %}

Related Clauses

• SELECT Main
• WHERE Clause
• GROUP BY Clause
• HAVING Clause
• SORT BY Clause
• CLUSTER BY Clause
• DISTRIBUTE BY Clause
• LIMIT Clause