Triggers and Remedies for Using Triggers in Oracle 9i Or Oracle 10g
In SQL, the TRUNCATE command is a Data Definition Language operation which marks the extent of a database for allocation. The result of such an operation often quickly eliminates all data in a table, effectively bypassing any further integrity checking mechanisms. It was first formally introduced in the SQL: 2008 standard. The intent is similar to that of the ALTER DYNAMICS or LIKE keyword in other procedural languages. However, while these commands have no syntactic scope in an ordinary database, they have strong implication when used in a well-known database.
Using the TRUNCATE command in SQL will mark a specific range of table rows as suspect. Whenever you try to access such rows, the server will automatically determine if it can safely remove this set of rows. The usual reasons why a deleted row in your database could remain accessible are due to two different situations. One of these situations involves the possibility of an application inserting data into a table that was not intended to be accessed; and the second situation involves the possibility of an application attempting to update data that has been permanently removed from your table.
Whenever the client requests a deleted row from your database, you will receive two SQL statements. The first of these SQL statements will indicate that an application tries to re-attempt the delete query with the TRUNCATE option enabled. The second SQL statement will indicate whether the server has flushed the table and all changes have been accounted for.
In many cases, you can safely assume that a TRUNCATE command in SQL will be appropriate. There are, however, some circumstances where you may need to use a VACUUM command in SQL to drop an entity. When there is a strong chance that the data that was once present on the affected tables could be recovered, but is no longer accessible due to the use of VACUUM, the server will drop it. For example, if you accidentally dropped a table in SQL and then performed a VACUUM command to drop the entire entity, there is a very good chance that the data will be left behind. If a developer uses the TRUNCATE option to drop the entity, it will be safe to assume that the data is permanently gone.
There are times when an application may want to execute a VACUUM or truncate command in SQL against the result that it receives from an Oracle database. In such cases, you will need to use the LIKE clause along with a CASE statement to determine if the result from an Oracle database would include the required data that needs to be included when performing the VACUUM or truncate statement. For example, if you were opening a new table and you needed to drop all of the records from the primary table, the developer would use the LIKE clause to check if all the data needed to be included in the drop is present and drop the entity. However, if the developer uses the Oracle connection to connect to the secondary table and uses the VACUUM command to drop all the records from the secondary table, then the developer would need to convert the secondary table into an Oracle database using the COPY command.
Performing a VACUUM or a SQL delete statement against a row in an Oracle table can result in unexpected behavior. If you try to drop a column from an existing database, but the stored procedure that was used to create the database does not drop the column, there is a good chance that the data on that particular column will not be dropped. If you try to drop a single column without waiting for the entire table to become stale, then you may end up getting data inconsistent with what you expected. Similarly, if you wait for the whole table to become empty before executing the SQL delete command, you may not get all the information you wanted because the Oracle server may realize that it needs to update the information for the row before it can erase it. In these cases, you cannot rely on the LIKE clause or any other clauses that can help you avoid getting inconsistent data.
There are times when the developer may execute a VACUUM or SQL delete statements against a row in an Oracle table and the developer forgets to specify the name of the table or the entity being dropped. In these cases, you have two options to overcome this problem. The first option is to provide the name of the entity or the table to which the deleted entity belongs. If you fail to provide the name of the entity being dropped in the SQL delete statement, then the system will assume that the entity was already removed from the current database and will attempt to drop the entity of the same name.
The second option is to provide the name of the entity or table that you want to be updated. For example, if you want to update the Employee table in your application, you can use the update query syntax for specifying the new primary key for the table. However, if you execute the same update query in a web application that uses Oracle, you cannot use the update command to update the Employee table in that application. To ensure consistency in your application, it is better to use the standard update command to update any type of entity, including tables and views.
Trimming of Column Values while Writing a Simple SQL Statement
In SQL Server, the most basic syntax for a Truntate in SQL statement is as follows:
TRUNCATELY FORGET STEP ONE: You can forget to truncate in sql delete statement. This is because when you manually delete an entity, SQL automatically leaves it empty. However, you cannot do this when you use the Trunced feature. The best solution in such circumstances is to use the automatic Trunced option. Just like other methods of Trunced in SQL above, there are several technical limitations with Trunced.
You cannot use an aggregate function on a Trunced view. You may try to, but here is a catch. When you call into an aggregate function, the processor will automatically copy the rows where the function has been applied. So, when you want to apply the aggregate on the Trunked table, you have to create a new view and then call it. This way, the query would not get affected.
TRUNCE IN SQL PORTUGuese language commands like DELETE, COMMIT, ROLLPDB, and DROP command does not allow any sort of transaction to be done on the tables in the database. So, they leave the tables untouched even after removing all the information stored on them. They just remove the records from the tables. Now, if you use the sql patching method for a table structure that is no longer accessible, you might end up losing your data.
TRUNCE IN SQL PASSPATH The Trunced table structure and other database objects are referenced by PASSPATH variable. You can reference it with a relative path in the server to prevent losing of data or integrity. But, it is a false sense to keep the data in this path. This will just lead to a hard disk failure. So, it is better to keep all the information flushed out of the server and keep the PASSPATH variable to ensure safety of information.
truncate in sql statements It works as the DELETE command when used on a static table. When you use such a table for any interactive user interface, you should be careful while issuing the DELETE command. If you have written an interactive application which uses connection to the database, you can send an sql broadcast to update the information on that particular table. When the user clicks on the Update button, an error will be shown. If the database is not closed properly, trunctate from the statement will be issued.
TRUNCE IN SQL command The TRUNCE IN SQL command is mostly used in Statement context. It works in two steps. It scans through the entire database to find any reference to any foreign key or reference to a single entity. Next, it tries to drop the entity reference. If it finds any entity with that name, it tries to delete it.
So, we can conclude that these two commands can be safely used. You just need to be careful while issuing them and gain expertise over using them. Also, make sure to close all the tables immediately after using them. Keep in mind that these two commands can also be used for cascading context. For more information on how to correctly use these two commands, please consult an expert.
Trimming unwanted information An important part of performing a Trimmedview is trimming the unwanted information. In the case of a standard view, you can easily get rid of unwanted information by using the standard query or update query commands. In case of a complex view, you need to use the TRUNCE IN SQL command to trim the unwanted data. You have to use the SQL TRUNCE option when you want to trim any data in a complex view. Also, the data that is being trashed out cannot be accessed by the user directly from the source tables, so it needs to be flushed out of the view first.
Trimming of columns In case of a complex view, performing Trimmedview with a simple select statement will be impossible. In order to perform Trimmed view, you have to create a new view, and then you can use the select statement to perform the Trimmed view. If you are performing a standard view, then you can simply use the SQL delete query to perform the Trimmed view. But, in case of complex views, you need to use the SQL update statement to perform the Trimmed view. Using the SQL update command with the type of ‘table’ name ‘trusted object’ will make the standard view into a trusted entity. In order to use the update query to perform a Trimmed view, you must create a ‘trusted object’ and then you can use the SQL delete statement to perform the Trimmed view.
Trimming of Column values If you are performing a complex view, then there are chances that you might find that some of the columns become unnecessary. If the number of the columns is more than the row size, then you can use the ‘drop-empty columns’ option from the view to drop those columns. But, if the number of the columns is less than the row size, you can use the’modify primary key’ option from the ‘drop-empty columns’ drop-down list to modify the primary key. Now, once the query is executed, a message appears like an error occurred while retrieving data. To fix such errors, you must use the ‘drop-empty columns’ option after writing the query.