@@ -18,5 +18,126 @@ license: |
1818 See the License for the specific language governing permissions and
1919 limitations under the License.
2020---
21+ The <code >ORDER BY</code > clause is used to return the result rows in a sorted manner
22+ in the user specified order. Unlike the <code >SORT BY</code > clause, this clause guarantees
23+ a total order in the output.
2124
22- ** This page is under construction**
25+ ### Syntax
26+ {% highlight sql %}
27+ ORDER BY { expression [ sort_direction | nulls_sort_oder ] [ , ... ] }
28+ {% endhighlight %}
29+
30+ ### Parameters
31+ <dl >
32+ <dt ><code ><em >ORDER BY</em ></code ></dt >
33+ <dd >
34+ Specifies a comma-separated list of expressions along with optional parameters <code>sort_direction</code>
35+ and <code>nulls_sort_order</code> which are used to sort the rows.
36+ </dd >
37+ <dt ><code ><em >sort_direction</em ></code ></dt >
38+ <dd >
39+ Optionally specifies whether to sort the rows in ascending or descending
40+ order. The valid values for the sort direction are <code>ASC</code> for ascending
41+ and <code>DESC</code> for descending. If sort direction is not explicitly specified, then by default
42+ rows are sorted ascending. <br><br>
43+ <b>Syntax:</b>
44+ <code>
45+ [ ASC | DESC ]
46+ </code>
47+ </dd >
48+ <dt ><code ><em >nulls_sort_order</em ></code ></dt >
49+ <dd >
50+ Optionally specifies whether NULL values are returned before/after non-NULL values, based on the
51+ sort direction. In Spark, NULL values are considered to be lower than any non-NULL values by default.
52+ Therefore the ordering of NULL values depend on the sort direction. If <code>null_sort_order</code> is
53+ not specified, then NULLs sort first if sort order is <code>ASC</code> and NULLS sort last if
54+ sort order is <code>DESC</code>.<br><br>
55+ <ol>
56+ <li> If <code>NULLS FIRST</code> (the default) is specified, then NULL values are returned first
57+ regardless of the sort order.</li>
58+ <li>If <code>NULLS LAST</code> is specified, then NULL values are returned last regardless of
59+ the sort order. </li>
60+ </ol><br>
61+ <b>Syntax:</b>
62+ <code>
63+ [ NULLS { FIRST | LAST } ]
64+ </code>
65+ </dd >
66+ </dl >
67+
68+ ### Examples
69+ {% highlight sql %}
70+ CREATE TABLE person (id INT, name STRING, age INT);
71+ INSERT INTO person VALUES
72+ (100, 'John', 30),
73+ (200, 'Mary', NULL),
74+ (300, 'Mike', 80),
75+ (400, 'Jerry', NULL),
76+ (500, 'Dan', 50);
77+
78+ -- Sort rows by age. By default rows are sorted in ascending manner.
79+ SELECT name, age FROM person ORDER BY age;
80+
81+ +-----+----+
82+ | name | age |
83+ +-----+----+
84+ | Jerry| null|
85+ | Mary | null|
86+ | John | 30 |
87+ | Dan | 50 |
88+ | Mike | 80 |
89+ +-----+----+
90+
91+ -- Sort rows in ascending manner keeping null values to be last.
92+ SELECT name, age FROM person ORDER BY age NULLS LAST;
93+
94+ +-----+----+
95+ | name | age |
96+ +-----+----+
97+ | John | 30 |
98+ | Dan | 50 |
99+ | Mike | 80 |
100+ | Mary | null|
101+ | Jerry| null|
102+ +-----+----+
103+
104+ -- Sort rows by age in descending manner.
105+ SELECT name, age FROM person ORDER BY age DESC;
106+
107+ +-----+----+
108+ | name | age |
109+ +-----+----+
110+ | Mike | 80 |
111+ | Dan | 50 |
112+ | John | 30 |
113+ | Jerry| null|
114+ | Mary | null|
115+ +-----+----+
116+
117+ -- Sort rows in ascending manner keeping null values to be first.
118+ SELECT name, age FROM person ORDER BY age DESC NULLS FIRST;
119+
120+ +-----+----+
121+ | name | age |
122+ +-----+----+
123+ | Jerry| null|
124+ | Mary | null|
125+ | Mike | 80 |
126+ | Dan | 50 |
127+ | John | 30 |
128+ +-----+----+
129+
130+ -- Sort rows based on more than one column with each column having different
131+ -- sort direction.
132+ SELECT * FROM person ORDER BY name ASC, age DESC;
133+
134+ +---+-----+----+
135+ | id | name | age |
136+ +---+-----+----+
137+ | 500| Dan | 50 |
138+ | 400| Jerry| null|
139+ | 100| John | 30 |
140+ | 200| Mary | null|
141+ | 300| Mike | 80 |
142+ +---+-----+----+
143+ {% endhighlight %}
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