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### 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 | DROP TABLE | DROP 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
DROP TABLE deletes the table and removes the directory associated with the table from the file system
if the table is not EXTERNAL table. If the table is not present it throws an exception.
In case of an external table, only the associated metadata information is removed from the metastore database.
If the table is cached, the command uncaches the table and all its dependents.
Syntax
DROP TABLE [ IF EXISTS ] table_identifier
Parameter
-
IF EXISTS
If specified, no exception is thrown when the table does not exist.
-
table_identifier
Specifies the table name to be dropped. The table name may be optionally qualified with a database name.
Syntax:
[ database_name. ] table_name
Examples
-- Assumes a table named `employeetable` exists.
DROP TABLE employeetable;
-- Assumes a table named `employeetable` exists in the `userdb` database
DROP TABLE userdb.employeetable;
-- Assumes a table named `employeetable` does not exist.
-- Throws exception
DROP TABLE employeetable;
Error: org.apache.spark.sql.AnalysisException: Table or view not found: employeetable;
(state=,code=0)
-- Assumes a table named `employeetable` does not exist,Try with IF EXISTS
-- this time it will not throw exception
DROP TABLE IF EXISTS employeetable;