How can I combine multiple rows of data into one row in SQL?

In SQL, you can use aggregate functions and the GROUP BY clause to combine multiple rows of data into a single row. Here are the specific steps:

1. Aggregate functions (such as SUM, MAX, MIN, etc.) are used to calculate the columns that need to be merged, combining multiple rows of data into one row.
2. Add a GROUP BY clause in the SELECT statement to group the columns that need to be aggregated.

For example, if there is a table containing sales order data with each order having multiple rows of product information, the following query can be used to merge the multiple rows of product information into one row:

SELECT order_id, SUM(quantity) AS total_quantity
FROM order_details
GROUP BY order_id;

In the above query, the order_details table contains data on order details, each order may have multiple rows of product information. The SUM(quantity) merges the product quantities of the same order into one row. Finally, the results are grouped by order_id to obtain the total product quantity for each order.

By using the above method, multiple lines of data can be combined into one row, allowing for data aggregation analysis.