【保存版】MariaDBで複数行挿入を使いこなす方法：詳細解説とサンプルコード

MariaDB における複数行挿入と複数サブクエリを用いた INSERT 文

複数サブクエリを用いる INSERT 文の構文

INSERT INTO table_name (column1, column2, ...)
SELECT expression1, expression2, ...
FROM subquery1;
UNION ALL
SELECT expression1, expression2, ...
FROM subquery2;
...
;

例

次の例では、customers テーブルに 2 つのサブクエリからデータを挿入します。

INSERT INTO customers (name, email, city)
SELECT first_name, email, city
FROM users;
UNION ALL
SELECT last_name, NULL, 'New York'
FROM users;
;

この例では、最初のサブクエリは users テーブルから first_name、email、city 列を選択し、customers テーブルに挿入します。2 番目のサブクエリは users テーブルから last_name 列のみを選択し、email 列は NULL に設定し、city 列は 'New York' に設定して customers テーブルに挿入します。

• 複雑なデータ操作を簡潔に記述できる
• 複数のデータソースからデータを挿入できる
• 重複レコードを排除できる

• サブクエリは同じ数の列を返す必要があり、列の順序も一致する必要がある
• サブクエリの結果セットの列型は、INSERT 文の対応する列の型と互換性がある必要がある

MariaDB の INSERT 文は、複数サブクエリを用いることで、複雑なデータ操作を簡潔に記述することができます。サブクエリを使用することで、複数のデータソースからデータを挿入したり、重複レコードを排除したりすることができます。

補足

• 上記の例は、あくまでも基本的な例です。実際の使用例では、より複雑なサブクエリや条件式を使用することもできます。
• 複数サブクエリを用いる INSERT 文は、パフォーマンス的に不利になる場合があります。大量のデータを挿入する場合は、他の方法を検討することをお勧めします。

Example 1: Inserting data from two tables into a single table

In this example, we will insert data from the users and addresses tables into the customers table. The users table contains user information such as name, email, and phone number, and the addresses table contains address information such as street address, city, and state. The customers table will combine the information from both tables.

INSERT INTO customers (name, email, phone_number, street_address, city, state)
SELECT users.name, users.email, users.phone_number, addresses.street_address, addresses.city, addresses.state
FROM users
INNER JOIN addresses
ON users.id = addresses.user_id;

In this example, we will insert data from the products table into the sales table. The products table contains product information such as product ID, name, and price. The sales table will store sales data for each product, including the sale date, quantity sold, and total amount. We will calculate the total amount by multiplying the quantity sold by the unit price.

INSERT INTO sales (product_id, sale_date, quantity_sold, total_amount)
SELECT product_id, CURRENT_DATE(), quantity, price * quantity
FROM products;

Example 3: Inserting data with conditional filtering

In this example, we will insert data from the orders table into the order_details table. The orders table contains order information such as order ID, customer ID, and order date. The order_details table will store details for each order item, including the product ID, quantity ordered, and unit price. We will only insert order details for orders that were placed within the last 30 days.

INSERT INTO order_details (order_id, product_id, quantity_ordered, unit_price)
SELECT orders.order_id, order_details.product_id, order_details.quantity_ordered, order_details.unit_price
FROM orders
INNER JOIN order_details
ON orders.order_id = order_details.order_id
WHERE orders.order_date >= DATE_SUB(CURRENT_DATE(), INTERVAL 30 DAY);

These are just a few examples of how to use multiple subqueries with the INSERT statement in MariaDB. The possibilities are endless, so be creative and use this powerful tool to solve your data manipulation needs.

Using the VALUES clause

The VALUES clause can be used to specify multiple rows of data to be inserted into a table. This method is simple and straightforward, but it can become cumbersome when dealing with a large number of rows or complex data.

INSERT INTO customers (name, email, city)
VALUES
  ('John Doe', '[email protected]', 'San Francisco'),
  ('Jane Doe', '[email protected]', 'New York'),
  ('Peter Jones', '[email protected]', 'London');

Using a loop with individual INSERT statements

You can use a loop to execute multiple INSERT statements, one for each row of data. This method is more flexible than using the VALUES clause, but it can be more verbose and error-prone.

DECLARE done INT DEFAULT 0;

WHILE NOT done DO
  SELECT name, email, city
  FROM users
  LIMIT 1
  INTO @name, @email, @city;

  IF @name IS NULL THEN
    SET done = 1;
  ELSE
    INSERT INTO customers (name, email, city)
    VALUES (@name, @email, @city);
  END IF;
END WHILE;

Using a temporary table

You can create a temporary table to store the data you want to insert, and then use a single INSERT statement to copy the data from the temporary table to the target table. This method can be useful when dealing with a large amount of data or when the data needs to be processed before being inserted.

CREATE TEMPORARY TABLE tmp_customers (
  name VARCHAR(255),
  email VARCHAR(255),
  city VARCHAR(255)
);

INSERT INTO tmp_customers (name, email, city)
SELECT first_name, email, city
FROM users;

INSERT INTO customers (name, email, city)
SELECT * FROM tmp_customers;

DROP TEMPORARY TABLE tmp_customers;

The best method for you will depend on the specific situation. Consider the following factors when choosing a method:

• Number of rows: If you are inserting a small number of rows, the VALUES clause or a loop with individual INSERT statements may be sufficient. For larger datasets, consider using a temporary table.
• Data complexity: If the data is simple and straightforward, the VALUES clause may be the easiest option. If the data is more complex or requires processing before being inserted, a temporary table or multiple subqueries may be a better choice.
• Performance: If performance is critical, consider using a temporary table or multiple subqueries. These methods can be more efficient than using the VALUES clause or a loop with individual INSERT statements.

I hope this helps!