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- Working with the Oracle Engine
- Various Oracle tools connected to the oracle engine
- Interaction between Oracle Clients and Oracle Engine and the server hard disk drive with data on it
- SQL
- SQL used for
- DML DCL DDL
- THE CREATE TABLE COMMAND
- INSERTION OF DATA INTO TABLES
- VIEWING DATA IN THE TABLES
- SQL Specific Questions
Interaction between Oracle Clients and Oracle Engine and the server hard disk drive with data on it.
What does SQL stand for?
Structured Query Language
How is SQL Different from NoSQL
The main difference is that SQL databases are structured (data is stored in the form of tables with rows and columns - like an excel spreadsheet table) while NoSQL is unstructured, and the data storage can vary depending on how the NoSQL DB is set up, such as key-value pair, document-oriented, etc.
What does it mean when a database is ACID compliant?
ACID stands for Atomicity, Consistency, Isolation, Durability. In order to be ACID compliant, the database much meet each of the four criteria
Atomicity - When a change occurs to the database, it should either succeed or fail as a whole.
For example, if you were to update a table, the update should completely execute. If it only partially executes, the update is considered failed as a whole, and will not go through - the DB will revert back to it's original state before the update occurred. It should also be mentioned that Atomicity ensures that each transaction is completed as it's own stand alone "unit" - if any part fails, the whole statement fails.
Consistency - any change made to the database should bring it from one valid state into the next.
For example, if you make a change to the DB, it shouldn't corrupt it. Consistency is upheld by checks and constraints that are pre-defined in the DB. For example, if you tried to change a value from a string to an int when the column should be of datatype string, a consistent DB would not allow this transaction to go through, and the action would not be executed
Isolation - this ensures that a database will never be seen "mid-update" - as multiple transactions are running at the same time, it should still leave the DB in the same state as if the transactions were being run sequentially.
For example, let's say that 20 other people were making changes to the database at the same time. At the time you executed your query, 15 of the 20 changes had gone through, but 5 were still in progress. You should only see the 15 changes that had completed - you wouldn't see the database mid-update as the change goes through.
Durability - Once a change is committed, it will remain committed regardless of what happens (power failure, system crash, etc.). This means that all completed transactions must be recorded in non-volatile memory.
Note that SQL is by nature ACID compliant. Certain NoSQL DB's can be ACID compliant depending on how they operate, but as a general rule of thumb, NoSQL DB's are not considered ACID compliant
When is it best to use SQL? NoSQL?
SQL - Best used when data integrity is crucial. SQL is typically implemented with many businesses and areas within the finance field due to it's ACID compliance.
NoSQL - Great if you need to scale things quickly. NoSQL was designed with web applications in mind, so it works great if you need to quickly spread the same information around to multiple servers
Additionally, since NoSQL does not adhere to the strict table with columns and rows structure that Relational Databases require, you can store different data types together.
What is a Cartesian Product?
A Cartesian product is when all rows from the first table are joined to all rows in the second table. This can be done implicitly by not defining a key to join, or explicitly by calling a CROSS JOIN on two tables, such as below:
Select * from customers CROSS JOIN orders;
Note that a Cartesian product can also be a bad thing - when performing a join on two tables in which both do not have unique keys, this could cause the returned information to be incorrect.
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SQL can create and maintain data manipulation objects such as tables, views, sequences etc.
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Data manipulation Objects will be create and stored on the server's hard disk drive, in a tabelspace, to which the user has been assigned.
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Once these data manipulation objects created, they are used extensively in commerical applications.
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SQL sentences that are used to create these objects are called DDL's or Data Definition Language.
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SQL sentences that are used to manipulate data within these objects are called DML's or Data Manipulation Language.
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SQL sentences that are used to control the behavior of these objects are called DCl's or Data Control Language.
Syntax:
CREATE TABLE tablename(columnname datatype(size), columnname datatype(size));CREATE TABLE syntax, the SQL statement starts with 'CREATE' i.e. a verb, followed by 'TABLE' i.e. a noun and '' i.e. adjective.
Example: Create a client_master table who structure is:
| Column Name | Data Type | Size |
|---|---|---|
| client_no | varchar2 | 6 |
| name | varchar2 | 20 |
| address1 | varchar2 | 30 |
| address2 | varchar2 | 30 |
| city | varchar2 | 15 |
| state | varchar2 | 15 |
| pincode | number | 6 |
| remarks | varchar2 | 60 |
| bal_due | number | 10,2 |
CREATE TABLE client_master (client_no varchar2(20), name varchar2(30), address1 varchar2(30),
address2 varchar2(30), city varchar2(15), state varchar2(15),
pincode number(6), remarks varchar2(60), bal_due number(10,2));Synatx:
INSERT INTO tablename(columnname, columnname) VALUES (expression, expression);Example: Insert the following values into the client_master table:
| Column Name | Values |
|---|---|
| client_no | C02000, |
| name | Abhinav Korpal |
| address1 | HSR Layout |
| address2 | Outer Ring |
| city | Bangalore |
| state | Karantaka |
| pincode | 560001 |
INSERT INTO client_master
(client_no, name, address1, address2, city, state, pincode)
VALUES('C02000', 'Abhinav Korpal', 'HSR Layout', 'Outer Ring', 'Bangalore', 'Karantaka', 560001);All Rows and All Column:
To View Global Table Data the syntax is:
Global data extract:
I) Syntax:
SELECT (columname1... ...columname n) FROM tablename;
II) Syntax:
SELECT * FROM tablename;Example:
- Retrieve the names of the employees and their salaries from the table emp_master;
SELECT name, salary FROM tablename;- Retrieve all records from tabel client_master;
SELECT * FROM client_master;The way of filtering table data will be
- Selected columns and all rows
- Selected rows and all columnns
- Selected columns and Selected rows
Syntax:
SELECT columname, columname FROM tablename; SELECT client_no, name FROM client_master;Syntax:
SELECT * FROM tablename WHERE search condition;Example: Retrive all client_information from table client_master the value in the bal_due field is greater than 0:
SELECT * FROM client_master WHERE bal_due > 0;Syntax:
SELECT columname, columnname FROM tablename WHERE search condition;Syntax:
SELECT ROWNUM, client_no, name
FROM client_master
WHERE ROWNUM < 8;Syntax:
CREATE SEQUENCES sequence_name
[INCREMENT BY integervalue
START WITH integervalue
MAXVALUE integervalue / NOMAXVALUE integervalue
MINVALUE integervalue / NOMINVALUE integervalue
CYCLE / NOCYCLE CACHE integervalue / NOCACHE
ORDER / NOORDER]Syntax:
DROP SEQUENCE sequence_name;Syntax:
GRANT {object privileges}
ON objectname
TO username
[WITH GRANT OPTION];Synatx:
REVOKE { object privileges }
ON objectname
FROM username;For these questions, we will be using the Customers and Orders tables shown below:
Customers
| Customer_ID | Customer_Name | Items_in_cart | Cash_spent_to_Date |
|---|---|---|---|
| 100204 | John Smith | 0 | 20.00 |
| 100205 | Jane Smith | 3 | 40.00 |
| 100206 | Bobby Frank | 1 | 100.20 |
ORDERS
| Customer_ID | Order_ID | Item | Price | Date_sold |
|---|---|---|---|---|
| 100206 | A123 | Rubber Ducky | 2.20 | 2019-09-18 |
| 100206 | A123 | Bubble Bath | 8.00 | 2019-09-18 |
| 100206 | Q987 | 80-Pack TP | 90.00 | 2019-09-20 |
| 100205 | Z001 | Cat Food - Tuna Fish | 10.00 | 2019-08-05 |
| 100205 | Z001 | Cat Food - Chicken | 10.00 | 2019-08-05 |
| 100205 | Z001 | Cat Food - Beef | 10.00 | 2019-08-05 |
| 100205 | Z001 | Cat Food - Kitty quesadilla | 10.00 | 2019-08-05 |
| 100204 | X202 | Coffee | 20.00 | 2019-04-29 |
How would I select all fields from this table?
Select *
From Customers;
How many items are in John's cart?
Select Items_in_cart
From Customers
Where Customer_Name = "John Smith";
What is the sum of all the cash spent across all customers?
Select SUM(Cash_spent_to_Date) as SUM_CASH
From Customers;
How many people have items in their cart?
Select count(1) as Number_of_People_w_items
From Customers
where Items_in_cart > 0;
How would you join the customer table to the order table?
You would join them on the unique key. In this case, the unique key is Customer_ID in both the Customers table and Orders table
How would you show which customer ordered which items?
Select c.Customer_Name, o.Item
From Customers c
Left Join Orders o
On c.Customer_ID = o.Customer_ID;
Using a with statement, how would you show who ordered cat food, and the total amount of money spent?
with cat_food as (
Select Customer_ID, SUM(Price) as TOTAL_PRICE
From Orders
Where Item like "%Cat Food%"
Group by Customer_ID
)
Select Customer_name, TOTAL_PRICE
From Customers c
Inner JOIN cat_food f
ON c.Customer_ID = f.Customer_ID
where c.Customer_ID in (Select Customer_ID from cat_food);
Although this was a simple statement, the "with" clause really shines when a complex query needs to be run on a table before joining to another. With statements are nice, because you create a pseudo temp when running your query, instead of creating a whole new table.
The Sum of all the purchases of cat food weren't readily available, so we used a with statement to create the pseudo table to retrieve the sum of the prices spent by each customer, then join the table normally.