Inserting data into one table from another table in Oracle can be accomplished using the INSERT INTO statement. The basic syntax for this statement is as follows:
INSERT INTO table1 (column1, column2, column3, ...)
SELECT column1, column2, column3, ...
FROM table2;
Here, table1 is the target table that you want to insert data into, and table2 is the source table from which you want to copy data. In the SELECT statement, you need to specify the columns that you want to insert into table1.
For example, if you have two tables named employee and new_employee and you want to insert data from new_employee into employee, you can use the following code:
INSERT INTO employee (employee_id, first_name, last_name, salary)
SELECT employee_id, first_name, last_name, salary
FROM new_employee;
In this example, the columns employee_id, first_name, last_name, and salary from the new_employee table are being inserted into the employee table.
You can also insert data from one table into another table by specifying a condition in the SELECT statement. For example, if you want to insert only the employees from the new_employee table whose salary is greater than $50000, you can use the following code:
INSERT INTO employee (employee_id, first_name, last_name, salary)
SELECT employee_id, first_name, last_name, salary
FROM new_employee
WHERE salary > 50000;
In this example, the WHERE clause specifies that only the rows from the new_employee table where the salary column is greater than $50000 will be inserted into the employee table.
It's also possible to insert data from one table into another table by using a subquery. A subquery is a query within a query. In this case, the subquery will be used to retrieve data from the source table, and the results of the subquery will be inserted into the target table. For example, if you want to insert only the employees from the new_employee table whose salary is the maximum salary in the new_employee table, you can use the following code:
INSERT INTO employee (employee_id, first_name, last_name, salary)
SELECT employee_id, first_name, last_name, salary
FROM new_employee
WHERE salary = (SELECT MAX(salary) FROM new_employee);
In this example, the subquery SELECT MAX(salary) FROM new_employee is used to retrieve the maximum salary from the new_employee table, and the results of the subquery are used in the WHERE clause to select only the employees from the new_employee table whose salary is the maximum salary.
It's also possible to insert data into multiple tables in a single INSERT INTO statement. For example, if you have three tables named employee, department, and location, and you want to insert data into all three tables, you can use the following code:
INSERT
In addition to inserting data from one table into another table, there are several other related topics that are important to understand when working with databases in Oracle.
One such topic is the use of the `MERGE` statement. The `MERGE` statement allows you to update data in one table based on data from another table. For example, if you have two tables named `employee` and `new_employee`, and you want to update the salary of the employees in the `employee` table based on the salary of the employees in the `new_employee` table, you can use the following code:
MERGE INTO employee e
USING new_employee ne
ON (e.employee_id = ne.employee_id)
WHEN MATCHED THEN
UPDATE SET e.salary = ne.salary;
In this example, the `MERGE INTO` statement is used to update the `employee` table based on data from the `new_employee` table. The `USING` clause specifies the source table, and the `ON` clause specifies the join condition. The `WHEN MATCHED` clause specifies that the `UPDATE` statement should be executed when a match is found between the `employee` and `new_employee` tables.
Another related topic is the use of the `CREATE TABLE AS SELECT` (CTAS) statement. The CTAS statement allows you to create a new table based on data from an existing table. For example, if you have a table named `employee` and you want to create a new table named `high_salary_employees` that contains only the employees with a salary greater than $50000, you can use the following code:
CREATE TABLE high_salary_employees AS
SELECT *
FROM employee
WHERE salary > 50000;
In this example, the `CREATE TABLE AS SELECT` statement is used to create a new table named `high_salary_employees` based on data from the `employee` table. The `SELECT` statement is used to retrieve only the rows from the `employee` table where the salary is greater than $50000.
Finally, it's also important to understand the use of the `UPDATE` statement. The `UPDATE` statement allows you to modify data in an existing table. For example, if you have a table named `employee` and you want to increase the salary of all employees by $1000, you can use the following code:
UPDATE employee
SET salary = salary + 1000;
In this example, the `UPDATE` statement is used to modify the data in the `employee` table by increasing the value of the `salary` column by $1000.
These are just a few of the many related topics that are important to understand when working with databases in Oracle. By understanding the use of these statements, you can perform a wide variety of operations on your data, including inserting data from one table into another table, updating data in an existing table, and creating new tables based on data from existing tables.
## Popular questions
1. How can you insert data from one table into another table in Oracle?
You can insert data from one table into another table in Oracle using the `INSERT INTO` statement. For example, if you have two tables named `employee` and `new_employee`, and you want to insert the data from the `new_employee` table into the `employee` table, you can use the following code:
INSERT INTO employee (employee_id, first_name, last_name, salary)
SELECT employee_id, first_name, last_name, salary
FROM new_employee;
In this example, the `INSERT INTO` statement is used to insert data into the `employee` table. The `SELECT` statement is used to retrieve the data from the `new_employee` table, and the `FROM` clause specifies the source table.
2. What is the difference between `INSERT INTO` and `CREATE TABLE AS SELECT` in Oracle?
The `INSERT INTO` statement is used to insert data into an existing table, whereas the `CREATE TABLE AS SELECT` (CTAS) statement is used to create a new table based on data from an existing table. For example, if you have a table named `employee` and you want to create a new table named `high_salary_employees` that contains only the employees with a salary greater than $50000, you can use the following code:
CREATE TABLE high_salary_employees AS
SELECT *
FROM employee
WHERE salary > 50000;
In this example, the `CREATE TABLE AS SELECT` statement is used to create a new table based on data from the `employee` table. The `SELECT` statement is used to retrieve only the rows from the `employee` table where the salary is greater than $50000.
3. Can you insert data from multiple tables into a single table in Oracle?
Yes, you can insert data from multiple tables into a single table in Oracle using the `INSERT INTO` statement. For example, if you have two tables named `employee` and `new_employee`, and you want to insert the data from both tables into a single table named `all_employees`, you can use the following code:
INSERT INTO all_employees (employee_id, first_name, last_name, salary)
SELECT employee_id, first_name, last_name, salary
FROM employee
UNION
SELECT employee_id, first_name, last_name, salary
FROM new_employee;
In this example, the `INSERT INTO` statement is used to insert data into the `all_employees` table. The `SELECT` statement is used to retrieve the data from the `employee` table, and the `FROM` clause specifies the source table. The `UNION` keyword is used to combine the results from both `SELECT` statements into a single result set.
4. How can you prevent duplicates when inserting data from one table into another table in Oracle?
You can prevent duplicates when inserting data from one table into another table in Oracle by using the `UNIQUE` keyword. For example, if you have two tables named `employee` and `new_employee`, and you want to insert the data from the `new_employee` table into the `employee` table, but you
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SQL Joins
