SQLite: SELECTクエリで取得したデータを別の表に転送する2つの主要な方法

SQLiteでSELECTクエリ結果を既存の表に挿入する方法

この操作には、主に以下の2つの方法があります。

方法1：INSERT INTO ... SELECT構文を使用する

最も基本的な方法は、INSERT INTO ... SELECT構文を使用する方法です。この構文は、SELECTクエリで取得した結果を、既存の表に挿入するために特化されています。

INSERT INTO target_table (column1, column2, ...)
SELECT column1, column2, ...
FROM source_table
WHERE condition;

説明:

• WHERE condition: 挿入するレコードを絞り込む条件（省略可）
• source_table: データを取得する元となるテーブル名
• column1, column2, ...: 挿入先の列名
• target_table: 挿入先のテーブル名

例:

-- customersテーブルから、注文金額が1000円を超える顧客情報をnew_customersテーブルに挿入する
INSERT INTO new_customers (customer_name, order_amount)
SELECT customer_name, order_amount
FROM customers
WHERE order_amount > 1000;

方法2：サブクエリを使用する

INSERT文の中にサブクエリを記述する方法もあります。この方法は、より柔軟な操作が可能ですが、少し複雑になります。

INSERT INTO target_table
VALUES (
  (SELECT value1 FROM source_table WHERE condition1),
  (SELECT value2 FROM source_table WHERE condition2),
  ...
);

• WHERE condition1, condition2: それぞれの値を取得する条件
• value1, value2, ...: 挿入する値

-- customersテーブルから、注文金額が1000円を超える顧客の名前と注文金額をnew_customersテーブルに挿入する
INSERT INTO new_customers
VALUES (
  (SELECT customer_name FROM customers WHERE order_amount > 1000),
  (SELECT order_amount FROM customers WHERE order_amount > 1000)
);

• 重複レコードの挿入を避けるために、OR IGNORE句を組み込むこともできます。
• データ型や列名の不一致などに注意する必要があります。
• 上記の例では、シンプルなクエリのみにて説明していますが、実際の操作では、結合や集計などの高度なクエリを組み合わせて利用することもできます。

Method 1: Using the INSERT INTO ... SELECT syntax

Example 1: Inserting customer records with order amount greater than 1000 from customers table to new_customers table

INSERT INTO new_customers (customer_name, order_amount)
SELECT customer_name, order_amount
FROM customers
WHERE order_amount > 1000;

Example 2: Inserting specific columns from customers table to new_customers table, applying a filter and renaming a column

INSERT INTO new_customers (modified_name, order_total)
SELECT customer_name AS modified_name, SUM(order_amount) AS order_total
FROM customers
WHERE order_date >= '2024-01-01'
GROUP BY customer_name;

Method 2: Using a subquery

INSERT INTO new_customers
VALUES (
  (SELECT customer_name FROM customers WHERE order_amount > 1000),
  (SELECT order_amount FROM customers WHERE order_amount > 1000)
);

Example 2: Inserting the highest order amount for each customer from customers table to max_orders table

INSERT INTO max_orders (customer_id, max_order_amount)
SELECT customer_id, MAX(order_amount)
FROM customers
GROUP BY customer_id;

Remember:

• Leverage subqueries for more complex data manipulation and filtering.
• Use OR IGNORE to prevent duplicate record insertion if needed.
• Ensure the data types and column names match between the source and target tables.

Temporary tables can be useful when you need to perform intermediate data transformations or aggregations before inserting the final results into the target table.

-- Create a temporary table 'temp_orders'
CREATE TEMPORARY TABLE temp_orders AS
SELECT customer_id, SUM(order_amount) AS total_order_amount
FROM orders
GROUP BY customer_id;

-- Insert data from the temporary table into the 'max_orders' table
INSERT INTO max_orders (customer_id, max_order_amount)
SELECT customer_id, MAX(total_order_amount)
FROM temp_orders;

Common Table Expressions (CTEs):

CTEs provide a way to define temporary result sets within a single SQL statement, making them suitable for complex data manipulations.

WITH order_totals AS (
  SELECT customer_id, SUM(order_amount) AS total_order_amount
  FROM orders
  GROUP BY customer_id
)

INSERT INTO max_orders (customer_id, max_order_amount)
SELECT customer_id, MAX(total_order_amount)
FROM order_totals;

Data Manipulation Functions:

In some cases, you might achieve the desired outcome using data manipulation functions directly within the INSERT statement.

INSERT INTO max_orders (customer_id, max_order_amount)
VALUES (customer_id, (
  SELECT MAX(order_amount)
  FROM orders
  WHERE customer_id = c.customer_id
))
FROM customers c;

Choosing the Right Method:

The most suitable method depends on the specific task and the complexity of the data manipulation.