How to Create Table In Oracle?

To create a table in Oracle, you can use the CREATE TABLE statement followed by the table name and columns with their data types and constraints. Here is a basic syntax example:

CREATE TABLE table_name ( column1 datatype [constraint], column2 datatype [constraint], ... );

You can define as many columns as needed in the table, along with constraints like NOT NULL, PRIMARY KEY, FOREIGN KEY, UNIQUE, etc. Once you have defined the structure of the table, you can execute the SQL statement to create the table in the Oracle database.

What is the ALTER TABLE statement used for in Oracle?

The ALTER TABLE statement in Oracle is used to add, modify or drop columns, constraints, and indexes in an existing table. It allows you to alter the structure of the table without needing to recreate it entirely.

How to specify column names and data types when creating a table in Oracle?

When creating a table in Oracle, you can specify column names and data types using the following syntax:

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CREATE TABLE table_name (
  column1_name data_type,
  column2_name data_type,
  ...
);

For example, if you were creating a table called "employees" with columns for "employee_id", "first_name", and "last_name", you would use the following SQL statement:

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CREATE TABLE employees (
  employee_id NUMBER,
  first_name VARCHAR2(50),
  last_name VARCHAR2(50)
);

In this example, "employee_id" is specified as a NUMBER data type, and both "first_name" and "last_name" are specified as VARCHAR2 data types with a maximum length of 50 characters.

You can also add constraints, such as specifying a column as a primary key or setting it to not allow null values, by adding additional clauses to the column definition. For example:

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CREATE TABLE employees (
  employee_id NUMBER CONSTRAINT pk_employee_id PRIMARY KEY,
  first_name VARCHAR2(50) NOT NULL,
  last_name VARCHAR2(50) NOT NULL
);

In this example, the "employee_id" column is specified as the primary key using the CONSTRAINT clause, and both "first_name" and "last_name" columns are specified as NOT NULL, meaning they cannot contain null values.

How to rename a column in an existing table in Oracle?

To rename a column in an existing table in Oracle, you can use the following SQL statement:

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ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name;

Replace table_name with the name of the table containing the column you want to rename, old_column_name with the current name of the column, and new_column_name with the new name you want to give to the column.

For example, if you have a table named "employees" and you want to rename the column "emp_id" to "employee_id", you would use the following SQL statement:

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ALTER TABLE employees RENAME COLUMN emp_id TO employee_id;

Make sure you have the necessary permissions to alter the table structure before executing the command.

How to create a table with a unique constraint in Oracle?

To create a table with a unique constraint in Oracle, you can use the following SQL statement:

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CREATE TABLE table_name (
    column1 datatype,
    column2 datatype,
    ...
    CONSTRAINT constraint_name UNIQUE (column1, column2, ...)
);

In this statement:

• table_name is the name of the table you want to create.
• column1, column2, etc. are the names of the columns in the table.
• datatype is the data type of each column.
• constraint_name is the name of the unique constraint.
• (column1, column2, ...) specifies the columns that should have unique values.

For example, to create a table named employees with a unique constraint on the employee_id column:

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CREATE TABLE employees (
    employee_id INT,
    first_name VARCHAR2(50),
    last_name VARCHAR2(50),
    CONSTRAINT unique_employee_id UNIQUE (employee_id)
);

This will create a table with the specified columns and a unique constraint on the employee_id column, ensuring that each value in that column is unique within the table.

What is the role of partitions in Oracle tables?

Partitions in Oracle tables are used to logically divide large tables into smaller, more manageable segments. This helps improve query performance, facilitate data management, and optimize storage utilization. By storing data in partitions, Oracle can efficiently access and retrieve only the data that is required, reducing the amount of data that needs to be processed during queries.

Some key roles of partitions in Oracle tables include:

1. Improved query performance: By storing data in partitions, Oracle can eliminate unnecessary data access and processing, leading to faster query performance. Queries can be directed to specific partitions, reducing the amount of data that needs to be scanned.
2. Enhanced data management: Partitions allow for easier organization and management of large tables, especially when dealing with historical or archival data. It becomes easier to add, remove, or archive partitions without disrupting the entire table structure.
3. Storage optimization: Partitions can be stored on different tablespaces or storage devices, enabling better utilization of storage resources. Frequently accessed data can be placed on faster storage devices, while older or less frequently accessed data can be stored on slower devices.
4. Partition pruning: Oracle can use partition pruning to skip unnecessary partitions when executing queries, further enhancing query performance. This can reduce the amount of data that needs to be accessed and processed.

Overall, partitions play a crucial role in optimizing the performance, management, and storage of large tables in Oracle databases.

What is the purpose of the TEMPORARY keyword when creating a table in Oracle?

The TEMPORARY keyword in Oracle is used to create a temporary table. Temporary tables are used to hold temporary data that is only needed for the duration of a session or a transaction. They are typically used for storing intermediate results in complex queries or for holding data temporarily while performing batch processing tasks.

The TEMPORARY keyword ensures that the table is only visible and accessible within the current session, and it is automatically dropped when the session ends or when the transaction is committed or rolled back. This helps to conserve database resources and prevent cluttering the database with unnecessary tables.

Overall, the purpose of the TEMPORARY keyword is to create a temporary table that is local to the current session or transaction, providing a convenient way to store temporary data without impacting the overall database structure.