So sánh truncate với delete oracel năm 2024
SQL Server cung cấp 2 phương pháp để xóa dữ liệu, DELETE và TRUNCATE. Cú pháp của hai lệnh này như sau: Show DELETE
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Khi cần xóa dữ liệu với điều kiện liên quan đến bảng khác:
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TRUNCATE không có tùy biến nào
Tuy cùng để xóa dữ liệu, nhưng hai lệnh này có những khác nhau cơ bản:
Vì những lý do trên, DELETE luôn luôn chậm hơn TRUNCATE. Càng có nhiều bản ghi DELETE càng chậm, còn TRUNCATE thì không phụ thuộc vào lượng dữ liệu. DELETE có phạm vi ứng dụng rộng hơn; còn TRUNCATE chỉ dùng được mỗi một việc, nhưng nó lại làm rất nhanh. Vì vậy, hãy nhớ dùng TRUNCATE khi có thể được. What’s the difference between truncating, deleting, and dropping a table in SQL? Find out in this article. There are a lot of ways to delete data in SQL, including the DELETE FROM name_table WHERE col=value; 0 commands. Which one should you use in a given situation? In this article, you’ll learn the syntax of each command in different database engines like MySQL, PostgreSQL, SQL Server, and Oracle. And you’ll understand the DELETE FROM name_table WHERE col=value; 0 vs. If you want to practice your SQL skills, I recommend our SQL learning platform LearnSQL.com. LearnSQL.com offers over 50 interactive SQL courses on various levels of proficiency. For example, try out our SQL Practice track with over 600 hands-on SQL exercises to practice your SQL skills. Now, let’s get started!
You can delete all records with the syntax: DELETE FROM name_table; Or you can delete a group of records using the WHERE clause: DELETE FROM name_table WHERE col=value; If you’d like to remove all records from a given table, use If you want to remove specific records, use DELETE FROM name_table WHERE col=value; 6 with filtering conditions, as in the second example. Let’s use these commands in an example. Here’s the table DELETE FROM name_table WHERE col=value; 7: idnameprice 1milk2.40 2bread3.68 3butter5.55 4sugar2.88 This query ... DELETE FROM product; … removes all the data in the table DELETE FROM name_table WHERE col=value; 7. After this query, the table DELETE FROM name_table WHERE col=value; 7 will be empty. But the DELETE FROM name_table WHERE col=value; 6 query ... DELETE FROM product WHERE price<2.90; … deletes only the records for milk and sugar, because their prices are lower than $2.90. (Milk is $2.40 and sugar is $2.88.) Now the table DELETE FROM name_table WHERE col=value; 7 only has records with prices higher than $2.90: idnameprice 2bread3.68 3butter5.55 How does DELETE work?If you don’t want to remove table structure or you’re only deleting specific rows, use the However,
Of course, to use the TRUNCATE TABLE
DELETE FROM name_table WHERE col=value; 6 clause. Here’s the syntax: TRUNCATE TABLE table_name; If you use this command, all rows in this table will be removed. The following query ... TRUNCATE TABLE product; … deletes all records stored in the table DELETE FROM name_table WHERE col=value; 7. How does TRUNCATE TABLE work?Be careful using this command. DELETE FROM product WHERE price<2.90; 5 transactions can be rolled back in database engines like SQL Server and PostgreSQL, but not in MySQL and Oracle. DELETE FROM product WHERE price<2.90; 5 is faster than Unlike DELETE FROM product WHERE price<2.90; 5 does not return the number of rows deleted from the table. It also resets the table auto-increment value to the starting value (usually 1). If you add a record after truncating the table, it will have ID=1. Note: In PostgreSQL, you can choose to restart or continue the auto-increment value. Oracle uses a sequence to increment values, which is not reset by DELETE FROM product WHERE price<2.90; 5. Of course, you need permission to use DELETE FROM product WHERE price<2.90; 5; in SQL Server, the minimum permission is TRUNCATE TABLE table_name; 5 table; in MySQL, you need the TRUNCATE TABLE table_name; 6 privilege. Finally, Oracle requires the TRUNCATE TABLE table_name; 7 system privilege to use this command. You can learn more in the course “The Basics of Creating Tables in SQL”, which is part of our . DROP TABLEThe DELETE FROM name_table WHERE col=value; 0 is another DDL (Data Definition Language) operation. But it is not used for simply removing data from a table; it deletes the table structure from the database, along with any data stored in the table. Here is the syntax of this command: DROP TABLE table_name; All you need after DELETE FROM name_table WHERE col=value; 0 is the name of the table you want to delete. For example, if you’d like to remove the entire DELETE FROM name_table WHERE col=value; 7 table from the database, you’d write: DROP TABLE product; This removes all data in the table DELETE FROM name_table WHERE col=value; 7 and the structure of the table. How does DROP TABLE work?The DELETE FROM name_table WHERE col=value; 0 operation removes the table definition and data as well as the indexes, constraints, and triggers related to the table. This command frees the memory space. No triggers are fired when executing DELETE FROM name_table WHERE col=value; 0. This operation cannot be rolled back in MySQL, but it can in Oracle, SQL Server, and PostgreSQL. In SQL Server, DELETE FROM name_table WHERE col=value; 0 requires TRUNCATE TABLE table_name; 5 permission in the schema to which the table belongs; MySQL requires the DROP privilege; Oracle the requires the TRUNCATE TABLE table_name; 7 privilege. In PostgreSQL, users can drop their own tables. DROP TABLE vs. DELETE TABLE vs. TRUNCATE TABLE in SQLWhich cases call for DELETE FROM name_table WHERE col=value; 0? When should you use DELETE FROM product WHERE price<2.90; 5 or opt for a simple DELETETRUNCATEDROP TypeDMLDDLDDL Uses a lockRow lockTable lockTable lock Works in WHEREYesNoNo Removes ...One, some, or all rows in a table.All rows in a table.Entire table structure: data, privileges, indexes, constraints, triggers. Resets ID auto-incrementNoMySQL: Yes Oracle: No PostgreSQL: User decides SQL Server: YesDoesn’t apply RollbackYesMySQL: No Oracle: No PostgreSQL: Yes SQL Server: YesMySQL: No Oracle: Yes PostgreSQL: Yes SQL Server : Yes Transaction loggingEach rowWhole table (minimal)Whole table (minimal) Works with indexed viewsYesNoNo Space requirementsMore spaceLess spaceMore space Fires triggersYesNoNo SpeedSlowFastestFaster Which operation is best for which use case?
You can learn more about creating database structures in our . In SQL, DROP TABLE table_name; 6 all have pluses and minuses. Hopefully, this article has helped you understand when and how to use each command. Truncate và DELETE khác nhau như thế nào?Như các bạn có thể thấy bản chất câu lệnh DELETE là xóa từng row khi có 109 rows đã bị tác động còn TRUNCATE đơn giản là xóa cả 1 dữ liệu của 1 bảng không kể số lượng dòng khi có 0 rows đã bị tác động. Truncate Table là gì?TRUNCATE TABLE được hiểu là một lệnh nhằm xóa tất cả dữ liệu trong 1 bảng của SQL Server. Ngoài ra bạn cũng có thể sử dụng DROP TABLE để xóa toàn bộ bảng nhưng tôi khuyên bạn nên hạn chế sử dụng lệnh này nếu chưa hiểu rõ. Truncate Oracle là gì?Khi sử dụng TRUNCATE, Oracle không thực hiện việc xóa dữ liệu hàng loạt, thay vào đó, nó chỉ xóa đi các liên kết đến dữ liệu. Điều này giúp cho việc xóa dữ liệu trở nên nhanh chóng hơn và đồng thời cũng giải phóng tài nguyên được sử dụng trước đó. |