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### What changes were proposed in this pull request? A few improvements to the sql ref SELECT doc: 1. correct the syntax of SELECT query 2. correct the default of null sort order 3. correct the GROUP BY syntax 4. several minor fixes ### Why are the changes needed? refine document ### Does this PR introduce any user-facing change? N/A ### How was this patch tested? N/A Closes #27866 from cloud-fan/doc. Authored-by: Wenchen Fan <wenchen@databricks.com> Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
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| layout | title | displayTitle | license |
|---|---|---|---|
| global | SELECT | WHERE clause | Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. |
The WHERE clause is used to limit the results of the FROM
clause of a query or a subquery based on the specified condition.
Syntax
{% highlight sql %} WHERE boolean_expression {% endhighlight %}
Parameters
boolean_expression-
Specifies any expression that evaluates to a result type
boolean. Two or more expressions may be combined together using the logical operators (AND,OR).
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, 'Dan', 50);
-- Comparison operator in WHERE clause.
SELECT * FROM person WHERE id > 200 ORDER BY id;
+---+----+---+
|id |name|age|
+---+----+---+
|300|Mike|80 |
|400|Dan |50 |
+---+----+---+
-- Comparison and logical operators in WHERE clause.
SELECT * FROM person WHERE id = 200 OR id = 300 ORDER BY id;
+---+----+----+
|id |name|age |
+---+----+----+
|200|Mary|null|
|300|Mike|80 |
+---+----+----+
-- IS NULL expression in WHERE clause.
SELECT * FROM person WHERE id > 300 OR age IS NULL ORDER BY id;
+---+----+----+
|id |name|age |
+---+----+----+
|200|Mary|null|
|400|Dan |50 |
+---+----+----+
-- Function expression in WHERE clause.
SELECT * FROM person WHERE length(name) > 3 ORDER BY id;
+---+----+----+
|id |name|age |
+---+----+----+
|100|John|30 |
|200|Mary|null|
|300|Mike|80 |
+---+----+----+
-- BETWEEN expression in WHERE clause.
SELECT * FROM person WHERE id BETWEEN 200 AND 300 ORDER BY id;
+---+----+----+
| id|name| age|
+---+----+----+
|200|Mary|null|
|300|Mike| 80|
+---+----+----+
-- Scalar Subquery in WHERE clause.
SELECT * FROM person WHERE age > (SELECT avg(age) FROM person);
+---+----+---+
|id |name|age|
+---+----+---+
|300|Mike|80 |
+---+----+---+
-- Correlated Subquery in WHERE clause.
SELECT * FROM person AS parent
WHERE EXISTS (
SELECT 1 FROM person AS child
WHERE parent.id = child.id AND child.age IS NULL
);
+---+----+----+
|id |name|age |
+---+----+----+
|200|Mary|null|
+---+----+----+
{% endhighlight %}