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### Mastering Data Manipulation: INSCERT, UPDATE, and DELETE Commands in SQL ###

This chapter delves into data manipulation in SQL, focusing on the INSERT, UPDATE, and DELETE commands. You'll learn how to add rows to existing tables using the INSERT command with proper syntax, including handling non-numeric data and NULL values. We also cover modifying existing rows with the UPDATE command and the importance of transaction control for committing or rolling back changes. Additionally, discover how to delete rows safely and manage table locks during these operations to ensure data integrity. ###

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### Mastering Data Manipulation: INSCERT, UPDATE, and DELETE Commands in SQL ###

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Presentation Transcript

  1. Chapter 10Data Manipulation

  2. INSERT Command • Used to add rows to existing tables • Identify table in the INSERT INTO clause • Specify data in the VALUES clause • Can only add one row at a time to a table

  3. INSERT Command Syntax • Enclose non-numeric data in single quotes • If column list not provided, a value must be assigned to each column in the table

  4. INSERT Command Example

  5. Inserting NULL Value • Omit column name from INSERT INTO clause column list • Substitute two single quotation marks • Use NULL keyword

  6. Inserting Data from an Existing Table Substitute subquery for VALUES clause

  7. Modifying Existing Rows • Modify rows using UPDATE command • Use UPDATE command to: • Add values to an existing row • Change existing values

  8. UPDATE Command • UPDATE clause identifies table • SET clause identifies column being changed and new value • Optional WHERE clause specifies row(s) to be changed – if omitted, will update all rows

  9. UPDATE Command Syntax

  10. UPDATE Command Example

  11. Substitution Variables • Prompts user for value • Identified by ampersand (&) preceding variable name • Can be used to create interactive scripts

  12. Substitution Variable Example

  13. Transaction Control • Results of Data Manipulation Language (DML) are not permanently updated to table until explicit or implicit COMMIT occurs • Transaction control statements can: • Commit data through COMMIT command • Undo data changes through ROLLBACK command

  14. COMMIT • Explicit COMMIT occurs by executing COMMIT; • Implicit COMMIT occurs when DDL command is executed or user properly exits system • Permanently updates table(s) and allows other users to view changes

  15. ROLLBACK • Used to “undo” changes that have not been committed • Occurs when: • ROLLBACK; is executed • System restarts after crash

  16. Deleting Rows DELETE command removes a row from a table

  17. DELETE Command – Omitting WHERE Clause Omitting WHERE clause removes all rows

  18. Table Locks • Prevents users from changing same data or objects • Two types: • Shared – prevents DML operations on portion of table • Exclusive – locks table preventing other exclusive or shared locks

  19. Shared Lock • Locks portion of table affected by DML operation • Implicitly occurs during UPDATE or DELETE operations • Explicitly occurs through LOCK TABLE command with SHARE MODE option • Released when COMMIT (implicit or explicit) or ROLLBACK occurs

  20. Exclusive Lock • Implicitly locks table for DDL operations - CREATE or ALTER TABLE • Explicitly locked through LOCK TABLE command with EXCLUSIVE MODE option • Released after execution of DDL operation or after user exits system

  21. SELECT…FOR UPDATE Command • Creates shared lock on retrieved portion of table • Prevents one user from changing a row while another user is selecting rows to be changed • Released through implicit or explicit commit

  22. SELECT…FOR UPDATE Command – Example

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