Чем отличается drop от truncate в sql

What is the Difference between DELETE, DROP and TRUNCATE?

The SQL DROP command is a DDL (Data Definition Language) command that deletes the defined table with all its table data, associated indexes, constraints, triggers, and permission specifications. The DROP command drops the existing table from the database. It only requires the name of the table to be dropped.

Syntax

The SQL DROP command works with the following syntax:

What is the DELETE Command in SQL?

The SQL DELETE command is a DML (Data Manipulation Language) command that deletes existing records from the table in the database. It can delete one or more rows from the table depending on the condition given with the WHERE clause. Thus the deletion of data is controlled according to the user's needs and requirements. The DELETE statement does not delete the table from the database. It just deletes the records present inside it and maintains a transaction log of each deleted row.

Syntax

The SQL DELETE command works with the following syntax:

What is the TRUNCATE Command in SQL?

The SQL TRUNCATE command is a DDL (Data Definition Language) command that modifies the data in the database. The TRUNCATE command helps us delete the complete records from an existing table in the database. It resets the table without removing it from the database. It does not use the WHERE clause like the DELETE command to apply the condition. It requires the table name to delete the records. It has faster performance due to the absence of conditions checking.

Syntax

The SQL TRUNCATE command works with the following syntax:

What is the Difference between DELETE, DROP and TRUNCATE Commands in SQL?

Let us look at the brief comparison of SQL's DROP , DELETE and TRUNCATE commands.

DELETE Command	DROP Command	TRUNCATE Command
Language	The DELETE command is Data Manipulation Language Command.	The DROP command is Data Definition Language Command.	The TRUNCATE command is a Data Definition Language Command.
Use	The DELETE command deletes one or more existing records from the table in the database.	The DROP Command drops the complete table from the database.	The TRUNCATE Command deletes all the rows from the existing table, leaving the row with the column names.
Transition	We can restore any deleted row or multiple rows from the database using the ROLLBACK command.	We cannot get the complete table deleted from the database using the ROLLBACK command.	We cannot restore all the deleted rows from the database using the ROLLBACK command.
Memory Space	The DELETE command does not free the allocated space of the table from memory.	The DROP command removes the space allocated for the table from memory.	The TRUNCATE command does not free the space allocated for the table from memory.
Performance Speed	The DELETE command performs slower than the DROP command and TRUNCATE command as it deletes one or more rows based on a specific condition.	The DROP Command has faster performance than DELETE Command but not as compared to the Truncate Command because the DROP command deletes the table from the database after deleting the rows.	The TRUNCATE command works faster than the DROP command and DELETE command because it deletes all the records from the table without any condition.
Integrity Constraints	The Integrity Constraints remain the same in the DELETE command.	The Integrity Constraints get removed for the DROP command.	The Integrity Constraints will not get removed from the TRUNCATE command.
Permission	DELETE permission is required to delete the rows of the table.	We need ALTER permission on the schema to which the table belongs and CONTROL permission on the table to use the DROP command.	We need table ALTER permission to use the TRUNCATE command.
Syntax	DELETE FROM table_name WHERE condition;	DROP TABLE table_name;	TRUNCATE TABLE table_name;

Example of DELETE, DROP, and TRUNCATE commands in SQL

DROP Example

Let us consider a table Student in the database.

The above SQL Query removes all the records and drops the table Student by removing it permanently from the database. The table removed using the DROP command can be retrieved back after execution.

DELETE Example

Let's consider the table Student with the following data.

Name	Roll_No
Nisha	101
Suman	102
Amish	103
Durgesh	104
Sarfaraz	105
Khansa	106

Let us understand the working of the DELETE command with the help of an example.

The table Student contains multiple rows. The above SQL Query helps us filter the appropriate row that needs to be deleted by the user. The WHERE clause helps us find the row with the student whose roll number is 101. The DELETE command deletes the row returned by the WHERE clause. In the above SQL query, the DELETE command deletes the record of student Nisha from the table whose roll number is 101.

The resulting table after the execution of the above SQL Query is:

Name	Roll_No
Suman	102
Amish	103
Durgesh	104
Sarfaraz	105
Khansa	106

TRUNCATE Example

Let's consider the table Student to understand the working of the TRUNCATE command in a better way.

The execution of the above SQL Query deletes all the records from the STUDENT table, leaving only the column names. It only removes the records from the table but doesn't remove the table from the database.

Difference between DROP and Truncate

Several SQL commands can be used to alter or remove data from a database. The two most frequently used commands are TRUNCATE and DROP. These two commands have the same purpose − to remove data from a database − but they operate and behave differently. Anybody working with SQL databases has to understand the distinction between DROP and TRUNCATE.

A complete table, including its structure, indexes, and data, can be deleted with the DROP command. Once performed, it is a permanent action that cannot be reversed. On the other hand, a table’s structure and indexes are preserved when all the data is removed from it using the TRUNCATE command. It is a transient action that can be reversed if necessary by using a transaction log.

What is DROP Command?

A database object, such as a table, index, or view, can be deleted from the database together with all of its related data and metadata by using the DROP command in SQL. The database object is permanently deleted and cannot be recovered when the DROP command is used. Depending on the object being dropped, the syntax for the DROP command differs. When employing the DROP command, it’s crucial to use caution since if used improperly, it can result in unwanted repercussions. For instance, dropping a table may result in the loss of all data it contains. Before using the DROP command, it is advised as best practise to create a backup of the database.

DROP Command – Advantages

Effective data management − The «drop» command can aid in effective data management by eliminating extraneous data, freeing up storage space, and enhancing system performance.

Enhanced security − By deleting critical data using the «drop» command, the risk of data breaches and unauthorised access to information is reduced.

Simple data deletion − Deleting data that is no longer required or is obsolete is simple and quick with the «drop» command.

DROP Command – Disadvantages

Possible deletion − The possibility of unintentional deletion is one of the «drop» command’s biggest drawbacks.

Action that cannot be undone − The «drop» command permanently deletes data from the system or software.

Negative Impacts − Using the «drop» command to remove a crucial piece of data or code can have a detrimental effect on how well an application or system functions, resulting in errors, crashes, and other problems.

What is TRUNCATE Command?

With the SQL TRUNCATE command, all rows from a table can be deleted while the table’s structure, metadata, and indexes are still present. In contrast to the DROP command, TRUNCATE just deletes the data from the table, not the database itself or any related metadata.

The data pages used to store the table’s data are reallocated when the TRUNCATE command is used, and the table’s identity value is also reset. This indicates that the identity value for the table’s initial insert operation will be 1.

The TRUNCATE command is a DDL (Data Definition Language) operation, not a DML (Data Manipulation Language) operation, which is crucial to keep in mind. As opposed to other techniques for deleting data from a database, TRUNCATE does not create any transaction logs, which can increase performance.

The TRUNCATE command is a potentially hazardous operation, so it is vital to use caution when performing it. TRUNCATE is an irreversible operation in contrast to DELETE, which can be reversed via a transaction log. Because of this, it is advised to create a backup of the table before running the TRUNCATE command.

TRUNCATE Command – Advantages

Faster than DELETE − When working with huge tables, the TRUNCATE command is significantly quicker than the DELETE command. This is because the DELETE command removes each row individually, but the TRUNCATE command merely removes the data from the table.

Reset the identity column − The TRUNCATE command resets the table’s identity column, enabling you to start the primary key values from scratch once more.

Reduces the size of the transaction log − The TRUNCATE command deletes all of the data from the table and reallocates the data pages it utilised, freeing up disc space.

TRUNCATE Command – Disadvantages

Action that cannot be undone − The TRUNCATE command cannot be undone. There is no method to get back data that has been deleted using it from a table. If you mistakenly truncate a table or need to preserve a record of the lost data, this could be a drawback.

WHERE is absent − The TRUNCATE command deletes all the data in the table, which can be a drawback if you only want to erase particular rows. This is in contrast to the DELETE command, which allows you to enter a WHERE clause to limit the rows to delete.

Resets all constraints − The TRUNCATE command resets all of the table’s constraints, including foreign key restrictions. You might need to manually recreate the foreign key restrictions if you truncate a table that is used as a reference by other tables.

DROP Vs TRUNCATE

The following table highlights the major differences between DROP and TRUNCATE −

The table definition and its data are deleted using the SQL DROP command.

All of the data in the table is deleted using the SQL TRUNCATE command.

The tablespace is released from the RAM by this query.

The tablespace is not released from the storage by the TRUNCATE query.

The DROP command doesn’t have a view for the table.

There is a tabular view available with the Truncate command.

The DROP command will automatically remove the integrity restrictions from the table.

This command’s integrity restrictions won’t be relaxed.

The removed space is not utilised in the DROP query.

Although less than the DELETE command, the removed space is still used.

Although the DROP query deletes data quickly, there are numerous issues.

In SQL, the TRUNCATE query executes more quickly than the DROP query.

Conclusion

To sum up, both the DROP and TRUNCATE commands are used to delete data from a SQL database, but they serve different purposes and have different functionality.

While the TRUNCATE command only removes the data from a table while leaving the table’s structure, metadata, and indexes intact, the DROP command permanently eliminates a database object along with all of its associated data and metadata. While often faster than DROP, the TRUNCATE command is a potentially hazardous operation that cannot be reversed.

To maintain the database’s integrity and performance, it’s critical to comprehend how these instructions differ from one another and to use them properly.

Чем отличается drop от truncate в sql

SQL commands are broadly classified into two types DDL, DML here we will be learning about DDL commands, and in DDL we will be learning about DROP and TRUNCATE in this article.

DROP is used to delete a whole database or just a table.

In this article, we will be learning about the DROP statement which destroys objects like an existing database, table, index, or view. A DROP statement in SQL removes a component from a relational database management system (RDBMS).

Syntax:

Examples 1:

To Drop a table

table_name: Name of the table to be deleted.

Examples 2:

To Drop a database

database_name: Name of the database to be deleted.

TRUNCATE

The major difference between TRUNCATE and DROP is that truncate is used to delete the data inside the table not the whole table.

TRUNCATE statement is a Data Definition Language (DDL) operation that is used to mark the extent of a table for deallocation (empty for reuse). The result of this operation quickly removes all data from a table, typically bypassing several integrity-enforcing mechanisms. It was officially introduced in the SQL:2008 standard. The TRUNCATE TABLE mytable statement is logically (though not physically) equivalent to the DELETE FROM mytable statement (without a WHERE clause).

Syntax:

TRUNCATE TABLE table_name;

table_name: Name of the table to be truncated.

DATABASE name – student_data

TRUNCATE

TRUNCATE SQL query removes all rows from a table, without logging the individual row deletions. TRUNCATE is faster than the DELETE query.

The following example removes all data from the Customers table.

1. TRUNCATETABLE Customers;
2. TRUNCATE is a DDL(Data Definition Language) command
3. TRUNCATE is executed using a table lock and the whole table is locked to remove all records.
4. We cannot use the WHERE clause with TRUNCATE.
5. TRUNCATE removes all rows from a table.
6. Minimal logging in the transaction log, so it is faster performance-wise.
7. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log.
8. Identify the column is reset to its seed value if the table contains an identity column.
9. To use Truncate on a table you need at least ALTER permission on the table.
10. Truncate uses less transaction space than the Delete statement.
11. Truncate cannot be used with indexed views.
12. TRUNCATE is faster than DELETE.

DELETE

SQL DELETE query deletes all records from a database table. To execute a DELETE query, delete permissions are required on the target table. If you need to use a WHERE clause in a DELETE, select permissions are required as well.

The following query deletes all rows from the Customers table.

1. DELETEFROM Customers;
2. GO

The following SQL query deletes all rows from the Customers table where OrderID is greater than 1000.

1. DELETEFROM Customers WHERE OrderId > 1000;
2. GO
3. DELETE is a DML(Data Manipulation Language) command.
4. DELETE is executed using a row lock, each row in the table is locked for deletion.
5. We can use where clause with DELETE to filter & delete specific records.
6. The DELETE command is used to remove rows from a table based on WHERE condition.
7. It maintains the log, so it slower than TRUNCATE.
8. The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row.
9. Identity of column keep DELETE retains the identity.
10. To use Delete you need DELETE permission on the table.
11. Delete uses more transaction space than the Truncate statement.
12. The delete can be used with indexed views.

DROP table query removes one or more table definitions and all data, indexes, triggers, constraints, and permission specifications for those tables. DROP command requires to ALTER permission on the schema to which the table belongs, CONTROL permission on the table, or membership in the db_ddladmin fixed database role.

The following SQL query drops the Customers table and its data and indexes from the current database.