Oracle Database SQL and PL/SQL Concepts
1. SQL SELECT Statement
The SQL SELECT statement is used to retrieve data from a database. It allows you to specify the columns you want to retrieve and the conditions that the rows must meet. The SELECT statement is fundamental for querying data in Oracle Database.
Example: Think of the SELECT statement as a librarian retrieving books from a library. Just as the librarian specifies the title and author to find the book, you specify the columns and conditions to retrieve the data.
2. SQL INSERT Statement
The SQL INSERT statement is used to add new rows of data into a table. It allows you to specify the values for each column in the new row. The INSERT statement is essential for adding new records to the database.
Example: Consider the INSERT statement as adding a new book to the library. Just as you provide details like title, author, and genre for the new book, you provide values for each column in the new row.
3. SQL UPDATE Statement
The SQL UPDATE statement is used to modify existing data in a table. It allows you to specify the columns to be updated and the conditions that the rows must meet. The UPDATE statement is crucial for maintaining accurate and up-to-date data.
Example: Think of the UPDATE statement as updating the details of a book in the library. Just as you correct the author's name or add a new edition, you modify the values in the existing rows.
4. SQL DELETE Statement
The SQL DELETE statement is used to remove rows from a table. It allows you to specify the conditions that the rows must meet for deletion. The DELETE statement is important for managing data and ensuring that obsolete records are removed.
Example: Consider the DELETE statement as removing a book from the library. Just as you remove a book that is no longer available, you delete rows that are no longer needed.
5. SQL JOIN
The SQL JOIN clause is used to combine rows from two or more tables based on a related column between them. It allows you to retrieve data from multiple tables in a single query. The JOIN clause is vital for querying related data across different tables.
Example: Think of the JOIN clause as combining two bookshelves in the library. Just as you combine books from different shelves based on a common theme, you combine rows from different tables based on a related column.
6. PL/SQL Procedures
PL/SQL procedures are named blocks of code that perform a specific task. They can be called from other PL/SQL blocks or SQL statements. Procedures are useful for encapsulating logic and reusing code in the database.
Example: Consider a PL/SQL procedure as a recipe in a cookbook. Just as a recipe provides step-by-step instructions to prepare a dish, a procedure provides step-by-step instructions to perform a task.
7. PL/SQL Functions
PL/SQL functions are similar to procedures but they return a value. They can be used in SQL statements and other PL/SQL blocks. Functions are useful for performing calculations and returning results.
Example: Think of a PL/SQL function as a calculator. Just as a calculator performs calculations and returns a result, a function performs operations and returns a value.
8. PL/SQL Triggers
PL/SQL triggers are named blocks of code that are automatically executed in response to certain events, such as INSERT, UPDATE, or DELETE operations on a table. Triggers are useful for enforcing business rules and maintaining data integrity.
Example: Consider a PL/SQL trigger as an alarm system. Just as an alarm system is triggered by certain events, a trigger is executed in response to specific database operations.
9. PL/SQL Cursors
PL/SQL cursors are used to handle the result sets returned by SQL queries. They allow you to fetch and process rows one at a time. Cursors are useful for iterating over large result sets and performing operations on each row.
Example: Think of a PL/SQL cursor as a conveyor belt in a factory. Just as the conveyor belt moves items one at a time, a cursor fetches rows one at a time from the result set.
10. PL/SQL Exceptions
PL/SQL exceptions are used to handle errors and unexpected conditions in PL/SQL code. They allow you to define custom error handling logic and ensure that your code behaves gracefully in case of errors.
Example: Consider PL/SQL exceptions as a safety net. Just as a safety net catches you when you fall, exceptions catch errors in your code and handle them appropriately.