How to implement a statement to query multiple rows of data in MySQL?

MySQL is a widely used open source relational database management system with many advantages such as fast, reliable, and easy to use. When operating a MySQL database, it is often necessary to query multiple rows of data. This article will discuss how to implement the query statement for multiple rows of data in MySQL and provide specific code examples.

1. Basic syntax

In MySQL, the SELECT statement is generally used to query multiple rows of data. The specific syntax is as follows:

SELECT column_name(s)
FROM table_name
WHERE condition
LIMIT row_count;

Among them, column_name(s) is the column name that needs to be queried, and multiple column names are separated by commas; table_name is the table name that needs to be queried; condition is The filter condition can be a conditional expression in the WHERE clause or the HAVING clause; row_count indicates the number of rows to be queried and can be omitted. When omitted, all rows that meet the conditions are queried.

2. Multi-condition query

In practical applications, multiple conditions generally need to be specified when querying multiple rows of data. For example, query the information of all students who are over 20 years old and over 170cm tall. At this time, you need to use the AND keyword to connect the two conditions. The specific syntax is as follows:

SELECT *
FROM students
WHERE age > 20 AND height > 170;

Among them, * means querying all columns, and students is the table name.

3. Fuzzy query

When only a part of the information to be queried is known, fuzzy query can be used. For example, query the information of all students whose last name is "Zhang". At this time, you can use the LIKE keyword for fuzzy matching. The specific syntax is as follows:

SELECT *
FROM students
WHERE name LIKE 'Zhang%';

where % means Any string, that is, matches all strings starting with "张".

4. Sorting query

In practical applications, when querying multiple rows of data, it is generally necessary to sort according to a certain condition. For example, querying all student information is sorted from high to low by height. At this time, you need to use the ORDER BY keyword to specify the column name and sorting method that need to be sorted. The specific syntax is as follows:

SELECT *
FROM students
ORDER BY height DESC;

where , DESC means descending order, ASC means ascending order.

5. Group query

When the queried data needs to be aggregated and calculated, group query needs to be used. For example, query the average age of each class. At this time, you need to use the GROUP BY keyword to specify the grouping column name and the function for aggregation calculation. The specific syntax is as follows:

SELECT class, AVG(age) AS avg_age
FROM students
GROUP BY class;

Among them, the AS keyword is used to alias the calculation results.

6. Specific code examples

The following provides an actual MySQL code example for querying multi-row data:

SELECT name, age, height
FROM students
WHERE gender = 'Male' AND age > 20
ORDER BY height DESC
LIMIT 10;

The above code will query the information of all students with male gender and age greater than 20 years old, and follow the The height is sorted from high to low, and the number of results is limited to 10 rows. The query results will return the name, age and height information of each student.

In short, in the MySQL database, statements for querying multi-row data can be implemented using basic syntax, multi-condition query, fuzzy query, sorting query, group query, etc., and can also be operated with the help of specific code examples.

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