6ea4b5fda7
### What changes were proposed in this pull request? Update public docs of SQL commands about altering cached tables/views. For instance: <img width="869" alt="Screenshot 2021-02-08 at 15 11 48" src="https://user-images.githubusercontent.com/1580697/107217940-fd3b8980-6a1f-11eb-98b9-9b2e3fe7f4ef.png"> ### Why are the changes needed? To inform users about commands behavior in altering cached tables or views. ### Does this PR introduce _any_ user-facing change? No ### How was this patch tested? By running the command below and manually checking the docs: ``` $ SKIP_API=1 SKIP_SCALADOC=1 SKIP_PYTHONDOC=1 SKIP_RDOC=1 jekyll serve --watch ``` Closes #31524 from MaxGekk/doc-cmd-caching. Authored-by: Max Gekk <max.gekk@gmail.com> Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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| layout | title | displayTitle | license |
|---|---|---|---|
| global | TRUNCATE TABLE | TRUNCATE TABLE | 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. |
Description
The TRUNCATE TABLE statement removes all the rows from a table or partition(s). The table must not be a view
or an external/temporary table. In order to truncate multiple partitions at once, the user can specify the partitions
in partition_spec. If no partition_spec is specified it will remove all partitions in the table.
If the table is cached, the command clears cached data of the table and all its dependents that refer to it. The cache will be lazily filled when the next time the table or the dependents are accessed.
Syntax
TRUNCATE TABLE table_identifier [ partition_spec ]
Parameters
-
table_identifier
Specifies a table name, which may be optionally qualified with a database name.
Syntax:
[ database_name. ] table_name -
partition_spec
An optional parameter that specifies a comma separated list of key and value pairs for partitions.
Syntax:
PARTITION ( partition_col_name = partition_col_val [ , ... ] )
Examples
-- Create table Student with partition
CREATE TABLE Student (name STRING, rollno INT) PARTITIONED BY (age INT);
SELECT * FROM Student;
+----+------+---+
|name|rollno|age|
+----+------+---+
| ABC| 1| 10|
| DEF| 2| 10|
| XYZ| 3| 12|
+----+------+---+
-- Removes all rows from the table in the partition specified
TRUNCATE TABLE Student partition(age=10);
-- After truncate execution, records belonging to partition age=10 are removed
SELECT * FROM Student;
+----+------+---+
|name|rollno|age|
+----+------+---+
| XYZ| 3| 12|
+----+------+---+
-- Removes all rows from the table from all partitions
TRUNCATE TABLE Student;
SELECT * FROM Student;
+----+------+---+
|name|rollno|age|
+----+------+---+
+----+------+---+