MySQL (full name: My Structured Query Language, Chinese name: Structured Query Language) is a widely used relational database management system with very powerful query capabilities. This article will mainly introduce the assignment operation in MySQL queries.
In MySQL, assignment operations use the "=" sign to assign values. For example, in the following table, we can assign values to the data row named Tom through the following statement:
UPDATE students SET score = 80 WHERE name = 'Tom';
In this statement, we use the "UPDATE" command to assign values to the data rows in the "students" table. The data is updated, modifying the value of the "score" field to 80. Among them, the "WHERE" statement specifies which data rows we want to assign values to. Here we specify a row of data named Tom.
In addition to direct assignment operations, MySQL also provides many other methods to update and modify data tables. For example:
1. Use " " and "-" signs to perform assignment operations.
In the following data table, we can use the following statement to accumulate the data rows named Tom:
UPDATE students SET score = score + 5 WHERE name = 'Tom';
In this statement, we use the " " sign to add the data rows named Tom in the data table. The "score" attribute is accumulated.
Similarly, we can use the "-" sign to subtract certain attributes, for example:
UPDATE students SET score = score - 5 WHERE name = 'Tom';
2. Perform assignment operations through subqueries.
In the following data table, we can use subqueries to assign values to the data rows named Tom:
UPDATE students SET score = (SELECT score FROM students WHERE name = 'Jack') WHERE name = 'Tom';
In this statement, we use a subquery statement to extract " The score information of the row of data "Jack" and assigned to the score attribute of the row of data "Tom".
3. Perform assignment operations through regular expressions (REGEXP).
In the following data table, we can use regular expressions to assign values to all names starting with "J":
UPDATE students SET score = 90 WHERE name REGEXP '^J';
In this statement, we use regular expressions "^J" matches all names starting with "J" and assigns all corresponding score attributes to 90.
While using the assignment operation, we also need to comprehensively consider the field types and data types of the data table to ensure the correctness and reliability of the assignment operation.
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