Can you please also add a test case where we drop a temporary table from a hive context? March 23, 2020 by Esat Erkec Temporary tables, also known as temp tables, are widely used by the database administrators and developers. And also I tried your suggestions, but it's not easy to cover both sql and hivesql dialect test code. Applying suggestions on deleted lines is not supported. The general syntax for dropping a view is as follows: Moreover, we can create a bucketed_user table with above-given requirement with the help of the below HiveQL.CREATE TABLE bucketed_user( firstname VARCHAR(64), lastname VARCHAR(64), address STRING, city VARCHAR(64),state VARCHAR(64), post STRI… I'd suggesting: You don't need this class. I have two questions here: 1) Will these files keep on growing for each and every insert? You must have the DROP privilege for each table. DROP [TEMPORARY] TABLE [IF EXISTS] tbl_name [, tbl_name] ... [RESTRICT | CASCADE] DROP TABLE removes one or more tables. yeah, I use a single logical operator here. privacy statement. The files are created as 0000_n.bz2 and they are still on disk. When you are looking for hive table please provide table name in lowercase, due to fact that spark.sqlContext.tableNames returns the array of table names only in lowercase. In SQL Server 2016, Microsoft introduced DIY or DROP IF EXISTS functionality. It removes the metadata, but the base table remains intact. "), DropTable(tableName, ifExists.nonEmpty, false), sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala, ExecutedCommand(RunnableDescribeCommand(planLater(o), describe.output)) :: Nil, ExecutedCommand(HiveDropTableCommand(drop.tableName, drop.isExists)) :: Nil. If it is an external table then the table entry will delete it from metastore but the data is available on HDFS Level. This query serves to split the input words into different rows of a temporary table aliased as temp. View all posts by Esat Erkec, © 2021 Quest Software Inc. ALL RIGHTS RESERVED. We have to underline one point about this statement; it works on SQL Server 2016 or the higher version of the SQL Server. I have two questions here: 1) Will these files keep on growing for each and every insert? Thanks in advance. hi, @liancheng, I think we do need this logical DropTable. Consequently, dropping of an external table does not affect the data. DROP TABLE [IF EXISTS] table_name [PURGE]; -- (Note: PURGE available in Hive 0.14.0 and later) DROP TABLE removes metadata and data for this table. http://dev.mysql.com/doc/refman/5.0/en/drop-table.html, @@ -454,7 +455,8 @@ https://cwiki.apache.org/confluence/display/Hive/Enhanced+Aggregation%2C+Cube%2C, @@ -230,7 +232,8 @@ private[hive] trait HiveStrategies {, This patch adds the following public classes. This results in the count column holding the number of occurrences for each word of the word column. <~ TABLE) ~ (IF ~ EXISTS).? "), ExecutedCommand(DropTempTable(table, isExists, temporary)) :: Nil, val tableExists = sqlContext.catalog.tableExists(Seq(tableName)), if (tableExists) sqlContext.dropTempTable(tableName), else logWarning(s"Unknown table '${tableName}'"), // no `IF EXISTS` keyword, will thorw an exception, else sys.error(s"Unknown table '${tableName}'"), sql/core/src/test/scala/org/apache/spark/sql/sources/TableScanSuite.scala, sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveQl.scala, val tableName = tableNameParts.map { case Token(p, Nil) => p }.mkString(". The temporary tables are used to store data for an amount of time in SQL Server. Test build #26505 has finished for PR 4060 at commit 998eb3b. Test build #26144 has finished for PR 4060 at commit dc1c9a0. When I have a table at my sqoop schema and want to delete it, I go to HIVE editor (through HUE) and key in the following command DROP TABLE IF EXISTS schemaName.tblName PURGE; After that the table disappeared form the gui of HUE (sqoop table list, metastore list) but the actual files of the table were not deleted from the HDFS. Sybase: check whether a temporary table exists Posted on April 5, 2012 April 29, 2012 by hb You can check for the existence of non-temporary tables (even in in tempdb) like this: However, it may be necessary to drop the temp table before creating it. The following query will create a local temporary table: Global Temporary Tables: The name of this type of temporary table starts with a double “##” hashtag symbol and can be accessed from all other connections. Extend HIVE-1856 to support IF EXISTS for {DROP TABLE, VIEW} and ALTER TABLE DROP PARTITION. Successfully merging this pull request may close these issues. table1) Use Impala LIKE statement along with CREATE TABLE: Hi, @liancheng Since all parser should go first ddlParser, if not get plan, then it will try dialect parser. His current interests are in database administration and Business Intelligence. You can use DROP IF EXISTS to drop any temporary table as well if it exists. Thanks for working on this! The idea behind this logic is pretty simple. If a temporary table has the same name as another one and a query specifies the table name without specifying the DB, the temporary table … Test build #26517 has finished for PR 4060 at commit b7146cc. to your account, DROP [TEMPORARY] TABLE [IF EXISTS] tbl_name, Also, refer to http://dev.mysql.com/doc/refman/5.0/en/drop-table.html. Hive Temporary Table … I'm not sure this logic is exactly right. 5. Test build #26311 has finished for PR 4060 at commit f047fda. answered Jun 26, 2019 by Gitika • … La sintaxis es la siguiente: DROP TABLE [IF EXISTS] table_name; La consulta siguiente cae una tabla denominada empleados: hive> DROP TABLE IF EXISTS employee; El éxito de la ejecución de la consulta, se llega a ver la siguiente respuesta: OK Time taken: 5.3 seconds hive>. Hive has a Internal and External tables. The types of temporary tables affect the life-cycle of the temporary tables. Syntax: TRUNCATE [TABLE] table_name [PARTITION partition_spec]; partition_spec: : (partition_column = partition_col_value, partition_column = partition_col_value, ...) TRUNCATE state is used to truncate a table or partitions in a table. Bugfix documented in the 5.1.40, 5.5.0, and 6.0.14 changelogs, as follows: When using row-based replication, DROP TEMPORARY TABLE IF EXISTS was written to the binary log if the table named in the statement did not exist, even though DROP TEMPORARY TABLE statement should never be logged in row-based mode, whether the table exists or not. You must have the DROP privilege for each table. SQL Server adds random numbers at the end of the local table variables names. In this method, we will check the existence of the temporary table with the help of the sys.tables because this table returns user tables in the relevant database. Be careful with this statement! When I am using DROP TABLE IF EXISTS in hive, it is not freeing the memory. As we can see, we check the existence of the #LocalCustomer table in the tempdb database, and if it exists, we have to drop it. It is a common practice to check whether the temporary table exists or not exists. There is no doubt that after these learnings, if we want to drop any temp table, we should work on the tempdb database. Tag: hive. Esat Erkec is a SQL Server professional who began his career 8+ years ago as a Software Developer. Sorry if I'm wrong. The optional IF EXISTS clause makes the statement succeed whether or not the table exists. Test build #26143 has finished for PR 4060 at commit 1e47f8a. Be careful with this statement! This capability is useful in standardized setup scripts that remove existing schema objects and create new ones. In this way, the SQL Server avoids the same name conflicts. For each table, it removes the table definition and all table data. If the session which has created the local temporary table is closed, the temporary table will be dropped automatically by SQL Server. However, with the help of CLUSTERED BY clause and optional SORTED BY clause in CREATE TABLE statement we can create bucketed tables. Instrucción Drop Table. At this point, we need to underline one issue, the table name is searched with the LIKE operator, and we also added the wildcard character at the end of the temp table name. In this way, we don’t experience the following error: To achieve this check, we can use different techniques. If it is an internal table then the table and data will complete delete. When you drop an Internal table, it drops the table from Metastore, metadata and it’s data files from the data warehouse HDFS location. We only need it for something like this: How about renaming DropTempTable to DropTable, and moving the if into it? 2. @liancheng Thanks for the code review, most of the them are very valueble for me. When you run DROP TABLE on an external table, by default Hive drops only the metadata (schema). OBJECT_ID function can take the object’s name as a parameter so we can use this function to check the existence of any object in the particular database. A temporary table is a convenient way for an application to automatically manage intermediate data generated during a complex query. In the actual planner we can match on the type of the table and delegate to the proper RunnableCommand. If the session where the global temporary table was created is closed, the global temporary table will be dropped automatically. However, Hive gives us access to something that is simply not possible with most other SQL technologies, External Tables. Thanks in advance. What is the difference between Clustered and Non-Clustered Indexes in SQL Server? He is a SQL Server Microsoft Certified Solutions Expert. Have a question about this project? Drop … As of Drill 1.8, you can include the IF EXISTS parameter with the DROP TABLE command. The following query will check the #LocalCustomer table existence in the tempdb database, and if it exists, it will be dropped. Enabling OFFLINE prevents the data in a table or partition from being queried, but the metadata can still be accessed. When you will drop/delete the table form the hive database, the table entry will delete it from hive metastore. Suggestions cannot be applied while the pull request is closed. Dropping an External table drops just the table from Metastore and the actual data in HDFS will not be removed. All RunnableCommand are automatically wrapped with ExecutedCommand in SparkStrategies.BasicOperators. ALTER TABLE in Hive. So, we can eliminate the “There is already an object named ‘#temptablename’ in the database” error during the temporary table creation. Already on GitHub? Rather than manually deleting tables needed only as temporary data in a complex query, Hive automatically deletes all temporary tables at the end of the Hive session in which they are created. On the other hand, global temporary tables are created with their original names. However, it may be necessary to drop the temp table before creating it. The files are created as 0000_n.bz2 and they are still on disk. Please merge with master and eliminate conflicts. Use DROP IF EXISTS command to drop temporary table if it is already exists in the Hive database: DROP TABLE IF EXISTS table1Temp; Step2: Create temporary table structure like original table … For each table, it removes the table definition and all table data. This suggestion is invalid because no changes were made to the code. If handle the type of the table and then delegate. If a base table is a view that is dropped, then the dependent view remains in an invalid state, which is either dropped or recreated. More than one different connection can create local temporary tables with the same name, so SQL Server automatically adds a random number at the end of this type of temporary table name. Impossible to create a temporary table with distributed DDL query on all cluster servers (by using ON CLUSTER): this table exists only in the current session. Once we add isTemporary to o.a.s.s.hive.execution.DropTable, you don't need this case branch. DROP TABLE [IF EXISTS] table_name [PURGE]; DDL DROP TABLE Example: In the below example, we are deleting the ‘employee’ table. ~ ident ^^ case temp ~ exists ~ tableName => DropTable(tableName, exists.nonEmpty, temp.nonEmpty) This comment has been minimized. Let us learn these techniques: OBJECT_ID function is used to obtain the identification number of the database object. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. This is the major difference between the local and global temporary tables. You can find him on LinkedIn. Such as, we can create indexes, statistics, and constraints for these tables like we do for persisted tables. Protection on data can be set at either the table or partition level. These are great ways to create Persisted and Temporary Tables from data that we already have access to within the notebook. 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It is a common practice to check whether the temporary table exists or not exists. Simply put, an External Table is a table built directly on top of a folder within a data source. When I am using DROP TABLE IF EXISTS in hive, it is not freeing the memory. If I remove this logical drop table, when execute drop table xxx, it will always use DropTableCommand in SQLContext. As of Drill 1.2, you can use the DROP TABLE command to remove tables (files or directories) from a file system when the file system is configured as a DFS storage plugin. [SPARK-5264][SQL] Support `drop temporary table [if exists]` DDL command, sql/core/src/main/scala/org/apache/spark/sql/sources/ddl.scala, (DROP ~> TEMPORARY.? You must change the existing code in this line in order to create a valid suggestion. Sorry if I'm wrong. signal an error if the to-be-dropped entity doesn't exist and IF EXISTS isn't specified; this behavior can be disabled by setting hive.exec.drop.ignorenonexistent to true You signed in with another tab or window. DROP TABLE IF EXISTS hql.customer PURGE; Underlying data in HDFS will be purged directly and table cannot be restored. Let’s see how to use it: Most of his career has been focused on SQL Server Database Administration and Development. See Storage Plugin Registration. Can't we just have one parser handle all drop table commands with a single logical operator. If not found I will construct a new MetastoreRelation for placeholder, it would be nice if you can give me some advice : ). As the best practices before creating a temporary table, we should check the existence of this temporary table. DROP [TEMPORARY] TABLE [IF EXISTS] tbl_name Also, refer to http://dev.mysql.com/doc/refman/5.0/en/drop-table.html In HiveContext. The ALTER TABLE statement in Hive enables you to change the structure of an existing table. This issue combines issues HIVE-1550 /1165/1542/1551: augment DROP TABLE/VIEW with IF EXISTS signal an error if the table/view doesn't exist and IF EXISTS wasn't specified introduce a flag in the configuration that allows you to turn off the new behavior Spark 2.0 or higher | GDPR | Terms of Use | Privacy. Example 2 - Error that occurs when using DROP TABLE without the IF EXISTS clause Esat Erkec is a SQL Server professional who began his career 8+ years ago as a Software Developer. Cannot be dropped by the other connections. This is the last technique on how to drop a temp table, which we will learn. This suggestion has been applied or marked resolved. Would you mind review this ? Suggestions cannot be applied on multi-line comments. If the table does exist, it is dropped; if it does not exist, the statement has no effect. The data is actually moved to the .Trash/Current directory if Trash is configured (and PURGE is not specified). Local Temporary Tables: The name of this type of temporary table starts with a single “#” hashtag symbol, and they are solely visible on the created session. Since the table being dropped does not exist in the first place, Hive throws an error, when we issue the command: DROP TABLE IF EXISTS table_name. He is a SQL Server Microsoft Certified Solutions Expert. Add this suggestion to a batch that can be applied as a single commit. The external table data is stored externally, while Hive metastore only contains the metadata schema. DROP TABLE IF EXISTS statement checks the existence of the table, and if the table exists, it drops. DROP [TEMPORARY] TABLE [IF EXISTS] tbl_name [, tbl_name] ... [RESTRICT | CASCADE] DROP TABLE removes one or more tables. And I think to use a logical node and use each dialect's own strategy to convert will more reasonable and easy to understand. Sign in Many features of the temporary tables are similar to the persisted tables. If any partition in a table has NO_DROP enabled, the table cannot be dropped either. Suggestions cannot be applied while viewing a subset of changes. Test build #26309 has finished for PR 4060 at commit 43ae1da. The following query will create a global temporary table: The following table expresses the main differences between global and local temporary tables: Names start with a single “#” hashtag symbol. I don't think that we need this boolean anymore. If you create a temporary table in Hive with the same name as a permanent table that already exists in the database, then within that session any references to that permanent table will resolve to the temporary table, rather than to the permanent table. Regards, Naga Vemprala <~ table) ~ (if ~ exists).? However, to keep the PR queue small, I propose we close this issue until you have time to update it. Enabling NO_DROP prevents a table from being dropped. In the following query, DROP TABLE IF EXISTS statement, we will check the #LocalCustomer table existence, and if it exists, it will be dropped. Thanks again for working on this. According to my thought, the best way is using the DROP TABLE IF EXISTS statement, but we can use other alternative methods easily. Step 1: Drop temporary table if it is already exists. Only one suggestion per line can be applied in a batch. we need catch exceptions in strategy. Names start with a double “##” hashtag symbol. Now, we will take a glance at them. In this tutorial, you will learn how to create, query, and drop an external table in Hive. By clicking “Sign up for GitHub”, you agree to our terms of service and Suggestions cannot be applied from pending reviews. After creating a local temporary table, if we check the temporary tables folder in tempdb, we will see a weird table name. I think we need to check both if it exists and if it is a temporary table. It can be a normal table (stored in Metastore) or an external table (stored in local file system); Hive treats both in the same manner, irrespective of their types. Tables can be accessed from all other sessions. Tables can be accessed only from the session where the table was created. The DROP VIEW command removes the view from the database. The GROUP BY WORD groups the results based on their keys. Temporary tables, also known as temp tables, are widely used by the database administrators and developers. new SchemaRDD(this, ddlParser(sqlText, false).getOrElse(HiveQl.parseSql(substituted))). Please omit the parenthesis. As we stated, local temp tables are created with random suffix so that we can not know the exact name of them. The convention when referencing ambiguous names is to do sources.DropTable. Example: Use DROP IF EXISTS command to drop temporary table if it is already exists in the Impala: DROP TABLE IF EXISTS table1Temp; Step 2: Create intermediate table structure same as original table (i.e. Using Automatic Plan Correction for Query Tuning, SQL Server Replication with a table with more than 246 columns, Overview of the Shrink TempDB database in SQL Server, An overview of the SQL Server Update Join, Different ways to SQL delete duplicate rows from a SQL Table, How to UPDATE from a SELECT statement in SQL Server, SQL Server table hints – WITH (NOLOCK) best practices, How to backup and restore MySQL databases using the mysqldump command, SQL multiple joins for beginners with examples, SQL Server functions for converting a String to a Date. Actually, you don't need DropTable or this case branch. Test build #26108 has finished for PR 4060 at commit df5d929. If you want the DROP TABLE command to also remove the actual data in the external table, as DROP TABLE does on a managed table, you need to configure the table properties accordingly. Truncate table. Test build #26764 has finished for PR 4060 at commit e7299aa. 2) Is there any DROP equivalent to remove the files as well on the disk? When you drop a table from Hive Metastore, it removes the table/column data and their metadata. I think we can add an isTemporary field to Hive DropTable, so that we don't bother introducing the newly introduced logical DropTable plan here. (drop ~> temporary.? Test build #26306 has finished for PR 4060 at commit e6f836b. Test build #26507 has finished for PR 4060 at commit 00ecc25. else if (conf.dialect == "hiveql") { We’ll occasionally send you account related emails. When we create a temporary table, they are created in the tempdb database. Is that ok to do like below? ~ ident ^^ {, case temp ~ exists ~ tableName => DropTable(tableName, exists.nonEmpty, temp.nonEmpty), sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala, sys.error("Tables dropped with SQLContext must be TEMPORARY, Use a HiveContext instead. In the following table, we can see all the methods that we have mentioned briefly: In this article, we learned the basics of the temporary tables, and we discussed dropping the temp table techniques in SQL Server. By adding IF EXISTS to the drop statement, you can drop the object only when it exists in the database.
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