SQL

Tutorials To understand some of the topics please analyze the following tutorials: The following tutorials will help:

What can we do with SQL Querying Data Single Table Multiple Tables Inserting Data Updating Data Deleting Data

Querying Data Querying Single Tables Basic Query Format Search Conditions Querying Multiple Tables

Querying Single Tables Basic Format: SELECT column(s) FROM table WHERE condition(s) Rules: SELECT must be first clause FROM must be second clause table/column names must be spelled as in the database

Selecting All Rows SELECT column(s) FROM table; Example: SELECT Customer_IDFROM Order_t;

Selecting Unique Rows SELECT DISTINCT column(s) FROM table; Example: SELECT DISTINCT Customer_ID FROM Order_t;

Search Conditions For retrieving specific rows: Comparison Operators Boolean Operators Other Operators Wildcards Expressions Functions Nulls SELECT column(s) FROM table WHERE ;

Comparison Operators SELECT Order_ID, Order_Date FROM Order_t WHERE Customer_ID = 1;

Comparison Operators, con’t... Comparison Operators: =equal to >greater than <less than >=greater than or equal to <=less than or equal to <>not equal to

Boolean Operators ANDall search conditions must be met ORany search condition must be met NOTa search condition must not be met SELECT Customer_ID, Order_ID, Order_Date FROM Order_t WHERE (Customer_ID = 1) AND (Order_ID > 1005);

Other Operators BETWEEN The BETWEEN... AND operator selects an inclusive range of data between two values. These values can be numbers, text, or dates. SELECT Customer_ID, Order_Date FROM Order_t WHERE Customer_ID BETWEEN 1 AND 5;

Wildcards * SELECT * FROM Order_t WHERE Customer_ID IN (1, 3, 5) You can use a "*" to select all columns. LIKE Like is a very powerful operator that allows you to select only rows that are "like" what you specify. The percent sign "%" can be used as a wild card to match any possible character that might appear before or after the characters specified. SELECT Customer_Name, Customer_ID FROM Customer_t WHERE Customer_Name LIKE (‘%furn%’); SELECT Customer_Name, Customer_ID FROM Customer_t WHERE Customer_Name LIKE (‘%furn_____’);

Min and Max Finds minimum/maximum value of attribute SELECT MAX(Order_Date) FROM Order_t; SELECT MIN(Order_Date) FROM Order_t WHERE Customer_ID > 8;

Nulls Means: unknown not applicable SELECT Customer_Name FROM Customer_t WHERE Customer_address IS NULL;

Querying Multiple Tables Joins Brings data together from multiple tables Same column in multiple tables Use table_name.column_name to distinguish columns Use WHERE clause to join tables Example SELECT Customer_t.Customer_ID, Customer_t. Customer_Name, Order_date FROM Customer_t, Order_t WHERE Order_date > (‘11/01/98’,’MM/DD/YY’) AND Customer_t.Customer_ID = Order_t.Customer_ID; ****Notice that the Customer_ID is the primary Key for Customer_t and Foreign key for order_t table**** This is the only way you can connect two tables !!!

Inserting Data INSERT INTO table_name [(column1_name, column2_name, …)] VALUES (column1_value, column2_value, …); Examples: INSERT INTO Order_t (order_id, customer_id) VALUES (9000,8);

Updating Data UPDATE table_name SET column1_name = new_value [,column2_name = new value,…] WHERE condition(s); Example: UPDATE Order_t SET Customer_ID = 2 WHERE Customer_ID = 1;

Deleting Data DELETE FROM table_name [WHERE condition(s)]; Examples: DELETE FROM Order_t WHERE Customer_ID = 2;