How to write mysql database query statement

MySQL query statement is a set of commands used to retrieve data from the database. The basic syntax includes: selecting column names (SELECT), specifying table names (FROM), adding conditions (WHERE), grouping data (GROUP) BY), set grouping conditions (HAVING), sort results (ORDER BY) and limit results (LIMIT). For example, to retrieve all customer information named "John": SELECT * FROM customers WHERE name = "John"; to retrieve the total order quantity: SELECT SUM(quantity) FROM orde

MySQL query statement writing guide

How to write a MySQL query statement?

MySQL query statements are commands used to retrieve data from a MySQL database. The basic syntax is as follows:

<code>SELECT 列名1, 列名2, ...
FROM 表名
WHERE 条件
GROUP BY 分组列
HAVING 分组条件
ORDER BY 排序列
LIMIT 限制条数</code>

Detailed steps:

1. Select the column to be retrieved (SELECT)

Use The SELECT clause specifies the column names to be retrieved.

2. Specify the source table (FROM)

Use the FROM clause to specify the table name where the data is located.

3. Add query conditions (WHERE)

Use the WHERE clause to specify the conditions that the records to be retrieved meet.

4. Group data (GROUP BY)

Use the GROUP BY clause to group data for aggregation functions (such as SUM() ,COUNT()).

5. Set grouping conditions (HAVING)

Use the HAVING clause to specify the conditions after grouping.

6. Sort results (ORDER BY)

Use the ORDER BY clause to specify the sorting column and specify ascending or descending order.

7. Limit results (LIMIT)

Use the LIMIT clause to limit the number of records returned.

Example query:

Retrieve all customer information named "John":

<code>SELECT *
FROM customers
WHERE name = "John";</code>

Retrieve the total order quantity from the "orders" table:

<code>SELECT SUM(quantity)
FROM orders
GROUP BY customer_id;</code>

Orders in the past 30 days sorted by date in descending order:

<code>SELECT *
FROM orders
WHERE order_date > DATE_SUB(NOW(), INTERVAL 30 DAY)
ORDER BY order_date DESC
LIMIT 10;</code>

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