MySQL adds, deletes and modifys operations need to pay special attention to accuracy and security. When inserting data, use the INSERT INTO table name (column) VALUES (value) syntax. The auto-increment primary key does not need to be filled in manually. Multiple records can be inserted at a time to improve efficiency. When modifying data, be sure to add WHERE conditions to the UPDATE statement to avoid updating the entire table. It is recommended to query and confirm the target record before modifying. When deleting data, DELETE must have WHERE conditions, otherwise the entire table will be cleared. If you need to reset the auto-increment ID, TRUNCATE TABLE can be used, but this operation cannot be rolled back and there are no WHERE conditions, so you must use it with caution.
When I first started using MySQL, adding, deleting and modifying were the most basic and most commonly used operations. Although they are simple, when they are actually used, they are prone to errors if they are not careful, such as accidentally deleting data, updating the wrong conditions, or inserting duplicate values. So these three contents must be clarified.
Insert data: How to write an INSERT statement?
The most common use of INSERT is to add a new record to the table. The basic syntax is:
INSERT INTO table name (column 1,column 2,column 3) VALUES (value 1, value 2, value 3);
For example, suppose you have a table called users , the fields have id , name and email , and you want to add a new user:
INSERT INTO users (name, email) VALUES ('Zhang San', 'zhangsan@example.com');
There is a detail to note here: If your id is the primary key that increases automatically, there is no need to fill it in manually, MySQL will automatically generate it for you. Another point is that inserting multiple records can write multiple brackets at a time, such as:
INSERT INTO users (name, email)
VALUES
('Li Si', 'lisi@example.com'),
('Wangwu', 'wangwu@example.com');This is much more efficient than execution.
Modify data: How to use UPDATE safely?
UPDATE is used to modify existing data. The syntax is probably like this:
UPDATE table name SET column = new value WHERE condition;
For example, if you want to change Zhang San's email address to a new address:
UPDATE users SET email = 'zhangsan_new@example.com' WHERE name = 'Zhang San';
??The key point is: Never forget to add WHERE conditions! If you accidentally miss it, the entire table field will be updated, and the consequences may be serious.
In addition, it is recommended to check the target record before executing UPDATE to confirm which ones you want to change. for example:
SELECT * FROM users WHERE name = 'Zhang San';
To add one more thing, if you want to change multiple fields at once, you can write it like this:
UPDATE users SET name = 'Li Si', email = 'new@example.com' WHERE id = 1001;
Delete data: DELETE Be especially careful
The purpose of DELETE is to delete records from the table. The basic format is:
DELETE FROM table name WHERE condition;
For example, if you want to delete a user whose name is "Zhang San":
DELETE FROM users WHERE name = 'Zhang San';
Like UPDATE, don't miss WHERE , otherwise the data of the entire table will be cleared.
Another common question is: If you just want to clear all data, you can use:
DELETE FROM users;
But if you still want to reset the self-increment ID, it is best to use:
TRUNCATE TABLE users;
However, TRUNCATE cannot be rolled back and cannot be equipped with WHERE conditions. Be cautious when using it.
Before actual operation, it is recommended to check it out:
SELECT * FROM users WHERE name = 'Zhang San';
Delete if there is no problem.
Basically these are the operations. INSERT, UPDATE, DELETE may seem simple, but you still need to be careful when using it, especially in the production environment, if you are not careful, you may have big problems. After being proficient, you can use it in conjunction with transactions, which is safer.
The above is the detailed content of mysql tutorial on INSERT, UPDATE, and DELETE. For more information, please follow other related articles on the PHP Chinese website!
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