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Managing Database Updates: COMMIT, ROLLBACK, and Table Modifications

DESCRIPTION

This chapter outlines key operations for managing data in a database. Updates to tables are temporary until explicitly committed or the session ends, which can affect data integrity. The COMMIT command makes updates permanent, while ROLLBACK reverses changes since the last commit. Learn how to change existing data using the UPDATE command, manage deletions with DELETE, create tables from existing data, alter table structures, add columns, and drop tables. These fundamental operations are crucial for effective database management.

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Managing Database Updates: COMMIT, ROLLBACK, and Table Modifications

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Presentation Transcript

  1. Chapter 5Updating Data

  2. COMMIT and ROLLBACK • Updates to a table • are temporary and can be cancelled at any time during the current work session • become permanent automatically when the DBMS is exited • Temporary updates can be made permanent immediately by running COMMIT command after first executing UPDATE command • Cancel updates with the ROLLBACK command • Updates since the last COMMIT command will be reversed (data only not structure changes)

  3. Changing Existing Data in a Table • Data stored in tables is subject to constant change • Keep data current by using UPDATE to change rows on which a specific condition is true • Format for the UPDATE command is • UPDATE <table name> SET <column name >= <new value>

  4. Updating a Table

  5. Deleting Existing Rows From a Table • To delete data from the database, use the DELETE command • Format for the DELETE command is • DELETE <table name> WHERE <column name> = <value>

  6. Deleting a Row

  7. Creating a New Table From An Existing Table • Use the CREATE TABLE command to describe the table • Use the INSERT command to add data to the table • Use the SELECT command to specify which rows from the existing table to insert into the new table

  8. Creating a Table From an Existing Table

  9. Changing a Table’s Structure • To change the structure of an existing table, use the ALTER TABLE command • The format for adding a new column is • ALTER TABLE <table name> ADD <column name> <characteristics>

  10. Adding a Column Using ALTER

  11. Changing Column Width

  12. Changing Columns to NOT NULL or NULL

  13. Making Complex Changes • Oracle does not allow you to • reduce the size of a column • to change a data type • To make these complex changes: • Use the CREATE TABLE command to describe the new table • insert values into it using the INSERT command combined with an appropriate SELECT command from the original table

  14. Dropping a Table • Delete a table using the DROP command • DROP ABLE SALES_REP

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