mysql query and modify

MySQL query and modify

MySQL is a very popular relational database management system used to store and manage large amounts of structured data. In MySQL, querying data is a very common operation, and modifying data is inevitable. Therefore, it is very important to query and modify data in MySQL. This article will introduce how to query and modify operations in MySQL.

Query data

In MySQL, query data using the SELECT statement. Data in the table can be obtained through the SELECT statement, but you need to specify the data columns you want to return. For example:

SELECT column1, column2, column3 FROM table_name;

This query statement will return the values ​​of columns "column1", "column2" and "column3" in the table "table_name". You can use the wildcard character "*" to retrieve the values ​​of all columns, as follows:

SELECT * FROM table_name;

This query statement will return the values ​​of all columns in the table "table_name".

You can also use the WHERE clause to limit the row data returned. For example:

SELECT * FROM table_name WHERE column1 = 'value';

This query statement will only return row data where the value of column "column1" in table "table_name" is "value". You can use various operators to define filter conditions (such as =, <>, <, >, LIKE, BETWEEN, etc.).

You can also use the ORDER BY clause to sort the result set by one or more columns. For example:

SELECT * FROM table_name ORDER BY column1 ASC;

This query statement sorts the values ​​of column "column1" in ascending order.

Modify data

In MySQL, use the UPDATE statement to modify data. The UPDATE statement allows you to update one or more rows of data in a table. For example:

UPDATE table_name SET column1 = 'new_value1', column2 = 'new_value2' WHERE column3 = 'value';

This UPDATE statement will match the condition "column3 = ' in the table "table_name" value'" row data, the values ​​of columns "column1" and "column2" are changed to "new_value1" and "new_value2" respectively.

If you want to update all row data, please do not use the WHERE clause, as shown below:

UPDATE table_name SET column1 = 'new_value1', column2 = 'new_value2';

This UPDATE statement changes the values ​​of columns "column1" and "column2" of all rows in table "table_name" to "new_value1" and "new_value2" respectively.

You can also use the DELETE statement to delete rows of data from the table. For example:

DELETE FROM table_name WHERE column1 = 'value';

This DELETE statement will delete the row data in the table "table_name" that meets the condition "column1 = 'value'".

Summary

This article introduces the basic syntax for querying and modifying data in MySQL. Query data using the SELECT statement, and modify data using the UPDATE and DELETE statements. You can use various operators and clauses to filter and sort query results, and use the WHERE clause to limit the rows of data to be updated or deleted.

To protect the data in the database, please remember to back up the database and use statements that modify and delete data carefully.

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