How to delete data in the data table

Method: 1. Use the DELETE statement to delete one or more rows of data in the table. The syntax is "DELETE FROM table name [WHERE clause]"; if the "WHERE clause" is omitted, you can delete the data in the table. All data. 2. Use the "TRUNCATE TABLE table name;" statement to delete all data in the table.

The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.

MySQL provides the DELETE and TRUNCATE keywords to delete data in the table.

1. DELETE statement

The DELETE statement can delete one or more rows of data in the table. Syntax format:

DELETE FROM <表名> [WHERE 子句] [ORDER BY 子句] [LIMIT 子句]

The syntax description is as follows:

• : Specify the name of the table to delete data.

  ORDER BY clause: Optional. Indicates that when deleting, rows in the table will be deleted in the order specified in the clause.

  WHERE clause: Optional. Indicates that the deletion conditions are limited for the deletion operation. If this clause is omitted, it means that all rows in the table are deleted.

  LIMIT clause: Optional. Used to tell the server the maximum number of rows to be deleted before the control command is returned to the client.

  Note: When the WHERE condition is not used, all data will be deleted.

  Example: Delete all data in the table

  mysql> DELETE FROM tb_courses_new;
  Query OK, 3 rows affected (0.12 sec)
  mysql> SELECT * FROM tb_courses_new;
  Empty set (0.00 sec)

  2. TRUNCATE statement

  The TRUNCATE keyword is used to completely clear a table. The syntax format is as follows:

  TRUNCATE [TABLE] 表名

  • The TABLE keyword can be omitted.

  Example: Delete all data in the table

  mysql> TRUNCATE TABLE tb_student_course;
  Query OK, 0 rows affected (0.04 sec)
  mysql> SELECT * FROM tb_student_course;
  Empty set (0.00 sec)

  (Recommended tutorial: mysql video tutorial)

  The difference between TRUNCATE and DELETE

  Logically speaking, the TRUNCATE statement has the same effect as the DELETE statement, but in some cases, there are differences in their use.

  • DELETE is a DML type statement; TRUNCATE is a DDL type statement. They are both used to clear the data in the table.

  • DELETE deletes records row by row; TRUNCATE directly deletes the original table and then creates an identical new table instead of deleting the data in the table row by row. Execute data faster than DELETE. Therefore, when you need to delete all data rows in the table, try to use the TRUNCATE statement to shorten the execution time.

  • DELETE After deleting data, the data can be retrieved with event rollback; TRUNCATE does not support transaction rollback, and data cannot be retrieved after deletion.

  • DELETE After deleting data, the system will not reset the counter of the auto-increment field; after TRUNCATE clears the table records, the system will reset the counter of the auto-increment field.

  • DELETE has a wider scope of use because it can delete part of the data by specifying conditions through the WHERE clause; TRUNCATE does not support the WHERE clause and can only delete the entire data.

  • DELETE will return the number of rows with deleted data, but TRUNCATE will only return 0, which is meaningless.

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