Multi-row Inserts in Oracle

Using the INSERT ALL Statement:

INSERT ALL INTO table_name (column1, column2, ...) VALUES (value1, value2, ...) INTO table_name (column1, column2, ...) VALUES (value1, value2, ...) ... SELECT * FROM dual;  

- **Explanation:**

- The `INSERT ALL` statement allows you to insert multiple rows into one or more tables in a single statement.
- Each `INTO` clause specifies a target table and its columns.
- The `VALUES` clause provides the data for each row.
- The `SELECT * FROM dual` clause is often used as a placeholder to indicate that the statement is an insert operation.

- **Example:**

```sql
INSERT ALL
INTO employees (employee_id, first_name, last_name, hire_date) VALUES (100, 'John', 'Doe', TO_DATE('01-JAN-2024', 'DD-MON-YYYY'))
INTO employees (employee_id, first_name, last_name, hire_date) VALUES (101, 'Jane', 'Smith', TO_DATE('15-FEB-2024', 'DD-MON-YYYY'))
SELECT * FROM dual;

Using a PL/SQL Block:

• Example:

  DECLARE
     CURSOR employee_cursor IS SELECT employee_id, first_name, last_name, hire_date FROM employees;
     employee_rec employee_cursor%ROWTYPE;
  BEGIN
     OPEN employee_cursor;
     LOOP
        FETCH employee_cursor INTO employee_rec;
        EXIT WHEN employee_cursor%NOTFOUND;
        -- Insert the row using employee_rec values
     END LOOP;
     CLOSE employee_cursor;
  END;
  

• Explanation:

  • A PL/SQL block provides more flexibility for complex insert operations.
  • You can declare variables to store data and use loops or other control structures to iterate over rows and insert them.

• DECLARE
     -- Declare variables
  BEGIN
     -- Insert rows using a loop or other logic
  END;
  

Using a Bulk Collect and Forall Statement:

• DECLARE
     TYPE employee_type IS TABLE OF employees%ROWTYPE;
     employee_collection employee_type;
  BEGIN
     SELECT * BULK COLLECT INTO employee_collection FROM employees;
     FORALL i IN 1..employee_collection.COUNT
        INSERT INTO employees_archive (employee_id, first_name, last_name, hire_date) VALUES (employee_collection(i).employee_id, employee_collection(i).first_name, employee_collection(i).last_name, employee_collection(i).hire_date);
  END;
  

• • This method is particularly efficient for inserting a large number of rows.
  • You first bulk collect rows into a collection and then use a FORALL statement to insert them in a single operation.

• DECLARE
     -- Declare a collection to store rows
  BEGIN
     -- Bulk collect rows into the collection
     FORALL i IN 1..collection.COUNT
        INSERT INTO table_name (column1, column2, ...) VALUES (collection(i).column1, collection(i).column2, ...);
  END;
  

Choosing the Best Method:

• For more complex inserts or large datasets, PL/SQL blocks or bulk collect/forall statements can be more efficient.
• For simple inserts with a small number of rows, the INSERT ALL statement is often sufficient.
• The best method depends on factors such as the number of rows to be inserted, the complexity of the insert operation, and performance requirements.

Understanding Multi-Row Inserts in Oracle

INSERT ALL
INTO table_name (column1, column2, ...) VALUES (value1, value2, ...)
INTO table_name (column1, column2, ...) VALUES (value1, value2, ...)
...
SELECT    * FROM dual;

INSERT ALL
INTO customers (customer_id, first_name, last_name) VALUES (101, 'John', 'Doe')
INTO customers (customer_id, first_name, last_name) VALUES (102, 'Jane', 'Smith')
SELECT * FROM dual;

• The SELECT * FROM dual clause is often used as a placeholder to indicate that the statement is an insert operation.
• The VALUES clause provides the data for each row.
• Each INTO clause specifies a target table and its columns.
• The INSERT ALL statement allows you to insert multiple rows into one or more tables in a single statement.

DECLARE
   -- Declare variables
BEGIN
   -- Insert rows using a loop or other logic
END;

DECLARE
   TYPE customer_type IS TABLE OF customers%ROWTYPE;
   customer_collection customer_type;
BEGIN
   -- Populate the collection with customer data
   SELECT * BULK COLLECT INTO customer_collection FROM customers;

   -- Insert rows using a FORALL loop
   FORALL i IN 1..customer_collection.COUNT
      INSERT INTO customers_archive (customer_id, first_name, last_name) VALUES (customer_collection(i).customer_id, customer_collection(i).first_name, customer_collection(i).last_name);
END;

• In this example, we use a bulk collect to efficiently fetch multiple rows into a collection and then insert them using a FORALL loop.

• Consider factors such as performance requirements, data volume, and the complexity of your insert logic when selecting the appropriate method.
• For more complex inserts or large datasets, PL/SQL blocks can be more efficient, especially when using bulk collect and FORALL.

Alternative Methods for Multi-Row Inserts in Oracle

While the methods discussed previously (using INSERT ALL and PL/SQL blocks) are common and effective, there are a few other alternatives worth considering:

Using a Dynamic SQL Statement

• Example:

  DECLARE
     stmt VARCHAR2(4000);
  BEGIN
     stmt := 'INSERT INTO customers (customer_id, first_name, last_name) VALUES (:1, :2, :3)';
     EXECUTE IMMEDIATE stmt USING 101, 'John', 'Doe';
  END;
  

• When to use: When you need to dynamically construct the insert statement based on runtime conditions or user input.

Using a Stored Procedure

• Example:

  CREATE PROCEDURE insert_customers (
     customer_id IN NUMBER,
     first_name IN VARCHAR2,
     last_name IN VARCHAR2
  ) AS
  BEGIN
     INSERT INTO customers (customer_id, first_name, last_name) VALUES (customer_id, first_name, last_name);
  END;
  

• When to use: When you need to encapsulate the insert logic into a reusable unit and potentially perform additional operations.

Using a Materialized View Log

• Example:

  CREATE MATERIALIZED VIEW LOG ON customers;
  
  CREATE TABLE customers_archive AS SELECT * FROM customers;
  
  CREATE TRIGGER customers_archive_trg
  AFTER INSERT ON customers
  REFERENCING NEW AS new ROW
  FOR EACH ROW
  BEGIN
     INSERT INTO customers_archive VALUES new;
  END;
  

• When to use: When you need to track changes to a table and efficiently insert new rows based on those changes.

Key considerations for choosing a method:

• Specific requirements: If you need to track changes or perform additional operations, materialized view logs or triggers may be appropriate.
• Maintainability: Stored procedures can improve code organization and maintainability.
• Flexibility: Dynamic SQL and stored procedures offer more flexibility, especially when dealing with varying conditions or complex logic.
• Performance: For large datasets, bulk insert methods like PL/SQL blocks with bulk collects and FORALL are often the most efficient.