How to change table fields in oracle

Oracle database is a world-class relational database management system. It is widely used in enterprise-level applications and data warehouses. Among them, the table is one of the most basic components of the database in the relational database architecture.

However, in the actual application process, we sometimes need to change the fields of the table, such as changing the field name, data type, length, etc. This article will introduce how Oracle changes the fields of a table.

1. Change the field name

Oracle allows you to change the field name of the table through the ALTER TABLE command. The specific syntax is as follows:

ALTER TABLE table_name RENAME COLUMN old_col_name TO new_col_name;

Among them, table_name represents the table name whose field name needs to be changed; old_col_name represents the field name that needs to be changed; new_col_name represents the new field name.

For example, if we need to rename a field named "employee_id" to "id", the ALTER TABLE statement is as follows:

ALTER TABLE employee RENAME COLUMN employee_id TO id;

2. Change the data type and length

Sometimes, we need to change the data type or length of table fields. Oracle also provides the ALTER TABLE command to achieve this purpose. The specific syntax is as follows:

ALTER TABLE table_name MODIFY column_name data_type(size);

Among them, table_name represents the table name whose field data type or length needs to be changed; column_name represents the field name that needs to be changed; data_type represents the new data type that needs to be changed; size represents the new field length.

For example, we need to change the data type of a field named "salary" from NUMBER to DECIMAL, with a length of 5, then the ALTER TABLE statement is as follows:

ALTER TABLE employee MODIFY salary DECIMAL(5);

3. Add and delete fields

In some cases, we need to add or delete table fields. Oracle provides ADD and DROP operations through which table fields can be added or deleted. The specific syntax is as follows:

Add operation:

ALTER TABLE table_name ADD (column_name1 data_type(size), column_name2 data_type(size), …);

Among them, table_name represents the table name of the field that needs to be added; column_name1, column_name2 represents the name of the field that needs to be added, data_type and size represent the field data type and length. .

For example, if we need to add an address field and a date of birth field to the employee table, the ALTER TABLE statement is as follows:

ALTER TABLE employee ADD (address VARCHAR(100), birthday DATE);

Delete operation:

ALTER TABLE table_name DROP COLUMN column_name;

Among them, table_name represents The table name of the field that needs to be deleted; column_name indicates the name of the field that needs to be deleted.

For example, if we need to delete the address field in the employee table, the ALTER TABLE statement is as follows:

ALTER TABLE employee DROP COLUMN address;

4. About constraints

What you need to pay attention to when changing table fields , changing the data type or length may cause the data format in the table to not comply with the defined constraints. Therefore, we need to check and determine the constraints before changing the fields. If necessary, we need to update the constraints before making changes. Common constraints include primary keys, unique fields, non-null constraints, foreign keys, etc. Changing constraints can be done through the ALTER TABLE command.

Summary:

The above are the methods and points to note when changing table fields in Oracle.

Change field name: ALTER TABLE table_name RENAME COLUMN old_col_name TO new_col_name;

Change data type and length: ALTER TABLE table_name MODIFY column_name data_type(size);

Add fields: ALTER TABLE table_name ADD (column_name1 data_type(size), column_name2 data_type(size), …);

Delete fields: ALTER TABLE table_name DROP COLUMN column_name;

It should be noted that when changing the table When using fields, you need to pay attention to constraints.

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