Удалить таблицу sql oracle
Обновлено: 05.07.2024
Summary: in this tutorial, you will learn how to use the Oracle drop column statements to remove one or more columns from a table.
Oracle Drop Column using SET UNUSED COLUMN clause
The process of dropping a column from a big table can be time and resource consuming. Therefore, we typically drop the column logically by using the ALTER TABLE SET UNUSED COLUMN statement as follows:
Once you execute the statement, the column is no longer visible for accessing.
During the off-peak hours, you can drop the unused columns physically using the following statement:
If you want to reduce the amount of undo logs accumulated, you can use the CHECKPOINT option that forces a checkpoint after the specified number of rows has been processed.
Oracle SET UNUSED COLUMN example
The following statements insert sample data into the suppliers table:
To logically drop the fax column from the suppliers table, you use the following statement:
You can view the number of unused columns per table from the DBA_UNUSED_COL_TABS view:
As you can see, the suppliers table has one unused column.
To drop the all unused columns from the suppliers table, you use the following statement:
Querying data from the DBA_UNUSED_COL_TABS view again, you will get an empty result set.
Oracle Drop Column using DROP COLUMN clause
To drop a column from a table physically, you use the following statement:
To drop multiple columns, you use the statement below:
Oracle DROP COLUMN clause example
The following statement removes the email and phone columns from the suppliers table:
In this tutorial, you have learned how to use the Oracle drop column statement to delete one or more columns from a table.
Use the DROP TABLE statement to move a table or object table to the recycle bin or to remove the table and all its data from the database entirely.
Unless you specify the PURGE clause, the DROP TABLE statement does not result in space being released back to the tablespace for use by other objects, and the space continues to count toward the user's space quota.
For an external table, this statement removes only the table metadata in the database. It has no affect on the actual data, which resides outside of the database.
When you drop a table that is part of a cluster, the table is moved to the recycle bin. However, if you subsequently drop the cluster, then the table is purged from the recycle bin and can no longer be recovered with a FLASHBACK TABLE operation.
Dropping a table invalidates dependent objects and removes object privileges on the table. If you want to re-create the table, then you must regrant object privileges on the table, re-create the indexes, integrity constraints, and triggers for the table, and respecify its storage parameters. Truncating has none of these effects. Therefore, removing rows with the TRUNCATE statement can be more efficient than dropping and re-creating a table.
CREATE TABLE and ALTER TABLE for information on creating and modifying tables
TRUNCATE TABLE and DELETE for information on removing data from a table
FLASHBACK TABLE for information on retrieving a dropped table from the recycle bin
The table must be in your own schema or you must have the DROP ANY TABLE system privilege.
You can perform DDL operations (such as ALTER TABLE , DROP TABLE , CREATE INDEX ) on a temporary table only when no session is bound to it. A session becomes bound to a temporary table by performing an INSERT operation on the table. A session becomes unbound to the temporary table by issuing a TRUNCATE statement or at session termination, or, for a transaction-specific temporary table, by issuing a COMMIT or ROLLBACK statement.
Dropping Private Temporary Tables
You can drop a private temporary table using the existing DROP TABLE command. Dropping a private temporary table will not commit an existing transaction. This applies to both transaction-specific and session-specific private temporary tables. Note that a dropped private temporary table will not go into the RECYCLEBIN .
Dropping Immutable Tables
Use the DROP TABLE statement to drop an immutable table. It is recommended that you include the PURGE option while dropping an immutable table. Dropping an immutable table removes its definition from the data dictionary, deletes all its rows, and deletes any indexes and triggers defined on the table.
The immutable table must be contained in your schema, or you must have the DROP ANY TABLE system privilege.
An immutable table can be dropped only after it has not been modified for a period of time that is defined by its retention period.
An empty immutable table can be dropped regardless of its retention period.
Specify the schema containing the table. If you omit schema , then Oracle Database assumes the table is in your own schema.
Specify the name of the table to be dropped. Oracle Database automatically performs the following operations:
All rows from the table are dropped.
All table indexes and domain indexes are dropped, as well as any triggers defined on the table, regardless of who created them or whose schema contains them. If table is partitioned, then any corresponding local index partitions are also dropped.
All the storage tables of nested tables and LOBs of table are dropped.
When you drop a range-, hash-, or list-partitioned table, then the database drops all the table partitions. If you drop a composite-partitioned table, then all the partitions and subpartitions are also dropped.
When you drop a partitioned table with the PURGE keyword, the statement executes as a series of subtransactions, each of which drops a subset of partitions or subpartitions and their metadata. This division of the drop operation into subtransactions optimizes the processing of internal system resource consumption (for example, the library cache), especially for the dropping of very large partitioned tables. As soon as the first subtransaction commits, the table is marked UNUSABLE . If any of the subtransactions fails, then the only operation allowed on the table is another DROP TABLE . PURGE statement. Such a statement will resume work from where the previous DROP TABLE statement failed, assuming that you have corrected any errors that the previous operation encountered.
You can list the tables marked UNUSABLE by such a drop operation by querying the status column of the *_TABLES , *_PART_TABLES , *_ALL_TABLES , or *_OBJECT_TABLES data dictionary views, as appropriate.
Oracle Database VLDB and Partitioning Guide for more information on dropping partitioned tables.
For an index-organized table, any mapping tables defined on the index-organized table are dropped.
For a domain index, the appropriate drop routines are invoked. Refer to Oracle Database Data Cartridge Developer's Guide for more information on these routines.
If any statistics types are associated with the table, then the database disassociates the statistics types with the FORCE clause and removes any user-defined statistics collected with the statistics type.
ASSOCIATE STATISTICS and DISASSOCIATE STATISTICS for more information on statistics type associations
If the table is not part of a cluster, then the database returns all data blocks allocated to the table and its indexes to the tablespaces containing the table and its indexes.
To drop a cluster and all its the tables, use the DROP CLUSTER statement with the INCLUDING TABLES clause to avoid dropping each table individually. See DROP CLUSTER.
If the table is a base table for a view, a container or master table of a materialized view, or if it is referenced in a stored procedure, function, or package, then the database invalidates these dependent objects but does not drop them. You cannot use these objects unless you re-create the table or drop and re-create the objects so that they no longer depend on the table.
If you choose to re-create the table, then it must contain all the columns selected by the subqueries originally used to define the materialized views and all the columns referenced in the stored procedures, functions, or packages. Any users previously granted object privileges on the views, stored procedures, functions, or packages need not be regranted these privileges.
If the table is a master table for a materialized view, then the materialized view can still be queried, but it cannot be refreshed unless the table is re-created so that it contains all the columns selected by the defining query of the materialized view.
If the table has a materialized view log, then the database drops this log and any other direct-path INSERT refresh information associated with the table.
Restrictions on Dropping Tables
You cannot directly drop the storage table of a nested table. Instead, you must drop the nested table column using the ALTER TABLE . DROP COLUMN clause.
You cannot drop the parent table of a reference-partitioned table. You must first drop all reference-partitioned child tables.
You cannot drop a table that uses a flashback data archive for historical tracking. You must first disable the table's use of the flashback data archive.
Specify CASCADE CONSTRAINTS to drop all referential integrity constraints that refer to primary and unique keys in the dropped table. If you omit this clause, and such referential integrity constraints exist, then the database returns an error and does not drop the table.
Specify PURGE if you want to drop the table and release the space associated with it in a single step. If you specify PURGE , then the database does not place the table and its dependent objects into the recycle bin.
You cannot roll back a DROP TABLE statement with the PURGE clause, nor can you recover the table if you have dropped it with the PURGE clause.
Using this clause is equivalent to first dropping the table and then purging it from the recycle bin. This clause lets you save one step in the process. It also provides enhanced security if you want to prevent sensitive material from appearing in the recycle bin.
Oracle Database Administrator's Guide for information on the recycle bin and naming conventions for objects in the recycle bin
Используя запрос DROP можно удалить таблицы (TABLE), индексы (INDEX) и базы данных (DATABASE).
DROP TABLE
DROP TABLE, применяемый в базе данных Oracle.
Обычно с таблицей в базе данных связано несколько объектов, например индекс, создаваемый первичным ключом, или ограничение UNIQUE, налагаемое на столбцы таблицы.
При удалении таблицы Oracle автоматически удаляет и любой связанный с ней индекс. Для удаления таблицы из БД необходимо выполнить команду DROP TABLE:
DROP TABLE Пример 1
Удаление таблицы:
Когда существуют ограничения для других таблиц, на которые ссылается удаляемая таблица, можно пользоваться каскадной конструкцией CASCADE CONSTRAINTS:
DROP TABLE. Пример 2
Удаление таблицы с ограничениями целостности:
DROP TABLE table CASCADE CONSTRAINTS;
DROP TABLE, применяемый в mySQL
DROP TABLE. Пример 3
Для удаления таблицы также используется запрос:
DROP TABLE. Пример 4
В случае, если необходимо установить проверку на существование таблицы при удалении (если существует удалить таблицу) запрос принимает следующий вид:
DROP TABLE IF EXISTS table;
Данный запрос будет выполнен в том случае, если удаляемая таблица существует в базе данных.
DROP INDEX
Данный запрос DROP INDEX используется для удаления индексов в таблице.
DROP INDEX, применяемый в базе данных Oracle:
Когда индекс в базе данных больше не нужен, разработчик может удалить его командой DROP INDEX. После удаления индекса эффективность поиска с использованием столбца или столбцов, ограниченных индексом, больше не повышается и упоминание об индексе исчезает из словаря данных. Индекс, применяемый для первичного ключа, удалить нельзя.
Синтаксис оператора DROP INDEX одинаков для удаления индекса любого типа (уникальности, битовой карты или В-дерева). Чтобы каким-то образом улучшить индекс, нужно сначала удалить его, а потом создать новый.
DROP INDEX. Пример 1
DROP INDEX my_index;
DROP INDEX, применяемый в mySQL:
DROP INDEX. Пример 2
Для удаления индексов (INDEX) используется запрос:
DROP INDEX my_index ON table;
Данный запрос удаляет индексы, указанные в my_index из таблицы table, но она не работает в версиях MySQL до 3.22. В версиях 3.22 и более поздних используется команда:
ALTER TABLE table_name DROP INDEX index_name;
DROP DATABASE
DROP DATABASE. Пример 1
DROP DATABASE database;
Запрос DROP DATABASE удаляет базу данных database.
TRUNCATE TABLE
Запрос TRUNCATE TABLE используется для того, чтобы удалить данные внутри таблицы, тем самым не затрагивая саму таблицу. В нужном случае TRUNCATE TABLE может быть очень полезен.
TRUNCATE TABLE, примеры использования TRUNCATE TABLE
TRUNCATE TABLE. Пример 1
TRUNCATE TABLE table;
DROP SEQUENCE
DROP SEQUENCE используется для удаления последовательности.
DROP SEQUENCE. Пример 1
DROP SEQUENCE sequence_name;
DROP SYNONYM
DROP SYNONYM используется для удаления синонимов.
DROP SYNONYM. Пример 1
DROP SYNONYM synonym_name;
Для удаления общих синонимов необходимо воспользоваться командой DROP PUBLIC SYNONYM.
DROP SYNONYM. Пример 2
DROP PUBLIC SYNONYM synonym_name;
Summary: in this tutorial, you will learn how to use the Oracle DROP TABLE statement to remove an existing table.
Introduction to Oracle DROP TABLE statement
To move a table to the recycle bin or remove it entirely from the database, you use the DROP TABLE statement:
In this statement:
Oracle DROP TABLE examples
Basic Oracle DROP TABLE example
The following CREATE TABLE statement creates persons table for the demonstration:
The following example drops the persons table from the database:
Oracle DROP TABLE CASCADE CONSTRAINTS example
The following statements create two new tables named brands and cars :
In these tables, each brand has 1 or more cars while each car belongs to only one brand.
The following statement tries to drop the brands table:
Oracle issued the following error:
This is because the primary key of the brands table is currently referenced by the brand_id column in the cars table.
The following statement returns all foreign key constraints of the cars table:
To drop the brands table, you must use the CASCADE CONSTRAINTS clause as follows:
This statement dropped not only the brands table but also the foreign key constraint fk_brand from the cars table.
If you execute again the statement to get the foreign key constraints in the cars table, you will not see any row returned.
Oracle DROP TABLE PURGE example
The following statement drops the cars table using the PURGE clause:
Drop multiple tables at once
Oracle provides no direct way to drop multiple tables at once. However, you can use the following PL/SQL block to do it:
This block deletes all tables whose names start with TEST_ .
To test this code, you can first create three tables: test_1 , test_2 and test_3 as follows:
Then, execute the PL/SQL block above.
In this tutorial, you have learned how to use the Oracle DROP TABLE statement to drop a table from the database.
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