Dec 8, 2010
What are the DBA tables in Oracle?
DBA_TABLES describes all relational tables in the database. Its columns are the same as those in ALL_TABLES . To gather statistics for this view, use the ANALYZE SQL statement.
What can you substitute for if exists?
An alternative for IN and EXISTS is an INNER JOIN, while a LEFT OUTER JOIN with a WHERE clause checking for NULL values can be used as an alternative for NOT IN and NOT EXISTS.
How do you use exists instead of in in Oracle?
The Exists keyword evaluates true or false, but the IN keyword will compare all values in the corresponding subuery column. If you are using the IN operator, the SQL engine will scan all records fetched from the inner query.
What happens if we drop a table?
Dropping a table removes the table definition from the data dictionary. All rows of the table are no longer accessible. All indexes and triggers associated with a table are dropped. All synonyms for a dropped table remain, but return an error when used.
Does the SQL view exists if the table is dropped from the database?
Answer: Yes, in Oracle, the SQL VIEW continues to exist even after one of the tables (that the SQL VIEW is based on) is dropped from the database. However, if you try to query the SQL VIEW after the table has been dropped, you will receive a message indicating that the SQL VIEW has errors.
How do I drop a user defined table?
Remove an alias data type or user-defined type (CLR) from the current database. Syntax DROP TYPE [schema.] type [ , ] Key type Name of the type (alias or user-defined) to be dropped. When a table is dropped, all associated triggers are automatically dropped.
Can we drop package in Oracle?
Use the DROP PACKAGE statement to remove a stored package from the database. If you omit this clause, then Oracle Database drops both the body and specification of the package. When you drop only the body of a package but not its specification, the database does not invalidate dependent objects.
Which is faster in or exists?
The EXISTS clause is much faster than IN when the subquery results is very large. Conversely, the IN clause is faster than EXISTS when the subquery results is very small. Also, the IN clause can’t compare anything with NULL values, but the EXISTS clause can compare everything with NULLs.
What is the difference between in and exists?
The main difference between them is that IN selects a list of matching values, whereas EXISTS returns the Boolean value TRUE or FALSE.
How do I get back a dropped table?
You can recover a dropped table by doing the following:Identify the dropped table by invoking the LIST HISTORY DROPPED TABLE command. Restore a database- or table space-level backup image taken before the table was dropped.Create an export directory to which files containing the table data are to be written.
Can a dropped table be recovered?
If a database backup doesn’t exist, a dropped table can be recovered from SQL database data and transaction log files. When it comes to recovery from a database in the Simple recovery model, it might fail as the Drop table transaction might have been overwritten. Even then, recovery is possible from the MDF file.
How do I delete a trigger in Oracle?
Use the DROP TRIGGER statement to remove a database trigger from the database. The trigger must be in your own schema or you must have the DROP ANY TRIGGER system privilege. To drop a trigger on DATABASE in another user’s schema, you must also have the ADMINISTER DATABASE TRIGGER system privilege.
What is the difference between DBA_TABLES and ALL_TABLES?
ALL_TABLES shows you the tables which the user you’re currently connected to has access to. This view has an additional column OWNER, to show the owning schema. DBA_TABLES shows you the tables in the database. This view has an additional column OWNER, to show the owning schema.
What are DBA tables?
DBA_TABLES describes all relational tables in the database. Its columns are the same as those in ALL_TABLES . To gather statistics for this view, use the ANALYZE SQL statement.
Which is better exists or in?
The EXISTS clause is much faster than IN when the subquery results is very large. Conversely, the IN clause is faster than EXISTS when the subquery results is very small. Also, the IN clause can’t compare anything with NULL values, but the EXISTS clause can compare everything with NULLs.
What happens when a table is dropped in Oracle?
Dropping a table removes the table definition from the data dictionary. All rows of the table are no longer accessible. All indexes and triggers associated with a table are dropped. All views and PL/SQL program units dependent on a dropped table remain, yet become invalid (not usable).
How do I restore a dropped table in Oracle 12c using flashback?
To recover the table we first check to see that it resides in the recyclebin, and then we issue the “flashback table to before drop” command to recover the table: SQL> drop table tarauni, Table dropped.
Can Delete be rolled back?
DELETE is a DML Command so it can be rolled back. The DELETE command returns the number of records that were deleted by its execution.
Can we flashback truncate table?
Caution: You cannot roll back a TRUNCATE TABLE statement, nor can you use a FLASHBACK TABLE statement to retrieve the contents of a table that has been truncated. You can check if you have an RMAN backup by logging into RMAN (rather than into the database) and using the LIST command.
How do you drop an object in Oracle?
Use the DROP TYPE statement to drop the specification and body of an object type, a varray, or a nested table type. See Also: DROP TYPE BODY for information on dropping just the body of an object type. CREATE TYPE and ALTER TYPE for information on creating and modifying types.
Can table-valued parameter be null?
As the User Define table Types are created as table-valued, so you cannot assign null to a table.
What happens when a package specification is dropped?
When you drop only the body of a package but not its specification, the database does not invalidate dependent objects. If you subsequently reference one of these objects, then the database tries to recompile the object and returns an error if you have not re-created the dropped package.
How do I drop a procedure in Oracle?
The syntax to a drop a procedure in Oracle is: DROP PROCEDURE procedure_name, procedure_name. The name of the procedure that you wish to drop.
What command removes triggers?
the DROP TRIGGER statement4. Which statement is used to remove a trigger? Explanation: In order to delete a trigger, the DROP TRIGGER statement is used. The DROP TRIGGER construct is used by writing the phrase ‘DROP TRIGGER’ followed by the scheme name specification.
What is dropping trigger?
Use the DROP TRIGGER statement to remove a database trigger from the database. If you omit schema , then Oracle Database assumes the trigger is in your own schema. trigger. Specify the name of the trigger to be dropped. Oracle Database removes it from the database and does not fire it again.
Is exists SQL efficient?
The EXISTS clause is much faster than IN when the subquery results is very large. Conversely, the IN clause is faster than EXISTS when the subquery results is very small. Also, the IN clause can’t compare anything with NULL values, but the EXISTS clause can compare everything with NULLs.
How replace exists in Oracle?
To an EXISTS is a simple matter of:Add a WHERE on the end of the internal SELECT FROM Table1 WHERE a IN( SELECT c FROM Table2 WHERE )Move the external match column (a) into the internal SELECT ‘s WHERE clause FROM Table1 WHERE IN( SELECT c FROM Table2 WHERE a )
When should I use exists?
To determine if any values are returned or not, we use EXISTS. 2. IN works faster than the EXISTS Operator when If the sub-query result is small. If the sub-query result is larger, then EXISTS works faster than the IN Operator.
Why exists is faster than in Oracle?
The EXISTS clause is much faster than IN when the subquery results is very large. Conversely, the IN clause is faster than EXISTS when the subquery results is very small. Also, the IN clause can’t compare anything with NULL values, but the EXISTS clause can compare everything with NULLs.
How do I find the owner of a table in Oracle?
I can find the owner of a table using : Select owner from dba_tables where table_name = ‘name_of_table_to_search’,
Why we use materialized view instead of a table?
Materialized views are basically used to increase query performance since it contains results of a query. They should be used for reporting instead of a table for a faster execution.
What are the default tables in Oracle?
Oracle / PLSQL: Oracle System TablesSystem TableDescriptionALL_TABLESDescription of relational tables accessible to the userALL_TAB_COLUMNSColumns of user’s tables, views and clustersALL_TAB_COL_STATISTICSColumns of user’s tables, views and clustersALL_TAB_COMMENTSComments on tables and views accessible to the user
Do you need to commit after drop table?
CREATE TABLE and DROP TABLE statements do not commit a transaction if the TEMPORARY keyword is used. SELECT causes an implicit commit before and after the statement is executed when you are creating nontemporary tables. (No commit occurs for CREATE TEMPORARY TABLE SELECT .)
What happens when you drop a table in Oracle?
Dropping a table removes the table definition from the data dictionary. All rows of the table are no longer accessible. All indexes and triggers associated with a table are dropped. All views and PL/SQL program units dependent on a dropped table remain, yet become invalid (not usable).
What happens if you drop a table on which a view exists?
When you drop a view, the definition of the view and other information about the view is deleted from the system catalog. All permissions for the view are also deleted. Any view on a table that is dropped by using DROP TABLE must be dropped explicitly by using DROP VIEW.
What happens to view if the table is dropped?
Answer: Yes, in Oracle, the SQL VIEW continues to exist even after one of the tables (that the SQL VIEW is based on) is dropped from the database. However, if you try to query the SQL VIEW after the table has been dropped, you will receive a message indicating that the SQL VIEW has errors.
Can a drop table be rolled back?
You cannot roll back a DROP TABLE statement. Note: For an external table, this statement removes only the table metadata in the database.
Do we need to commit after drop table?
CREATE TABLE and DROP TABLE statements do not commit a transaction if the TEMPORARY keyword is used. SELECT causes an implicit commit before and after the statement is executed when you are creating nontemporary tables. (No commit occurs for CREATE TEMPORARY TABLE SELECT .)
Can we drop a table that has dependent views on it?
Only its owner may destroy a table. (CASCADE will remove a dependent view entirely, but in the foreign-key case it will only remove the foreign-key constraint, not the other table entirely.)
What happens to the data associated with a view when the view is dropped?
Anytime you DROP anything using the SQL DROP command, you should feel a little nervous tension. After all, something is being removed (possibly permanently) from the database! However, with by dropping a view, the original data is unaffected.