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VI.1.1 SQL Tutorial

What is SQL?

SQL (pronounced "ess-que-el") stands for Structured Query Language. SQL is used to communicate with a database. According to ANSI (American National Standards Institute), it is the standard language for relational database management systems. SQL statements are used to perform tasks such as update data on a database, or retrieve data from a database. Some common relational database management systems that use SQL are: Oracle, Sybase, Microsoft SQL Server, Access, Ingres, etc. Although most database systems use SQL, most of them also have their own additional proprietary extensions that are usually only used on their system. However, the standard SQL commands such as "Select", "Insert", "Update", "Delete", "Create", and "Drop" can be used to accomplish almost everything that one needs to do with a database. This tutorial will provide you with the instruction on the basics of each of these commands as well as allow you to put them to practice using the SQL Interpreter.

 

Table Basics

A relational database system contains one or more objects called tables. The data or information for the database are stored in these tables. Tables are uniquely identified by their names and are comprised of columns and rows. Columns contain the column name, data type, and any other attributes for the column. Rows contain the records or data for the columns. Here is a sample table called "weather".

city, state, high, and low are the columns. The rows contain the data for this table:

 

Weather
city state high low
Phoenix Arizona 105 90
Tucson Arizona 101 92
Flagstaff Arizona 88 69
San Diego California 77 60
Albuquerque New
Mexico
80 72

 

 

Selecting Data

The select statement is used to query the database and retrieve selected data that match the criteria that you specify. Here is the format of a simple select statement:

select "column1"
[,"column2",etc]
from "tablename"
[where "condition"];
[] = optional

The column names that follow the select keyword determine which columns will be returned in the results. You can select as many column names that you'd like, or you can use a "*" to select all columns.

The table name that follows the keyword from specifies the table that will be queried to retrieve the desired results.

The where clause (optional) specifies which data values or rows will be returned or displayed, based on the criteria described after the keyword where.

Conditional selections used in the where clause:

= Equal
> Greater than
< Less than
>= Greater than or equal
<= Less than or equal
<> Not equal to
LIKE *See note below

The LIKE pattern matching operator can also be used in the conditional selection of the where clause. 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. For example:

 

Sample Table: empinfo
first last id age city state
John Jones 99980 45 Payson Arizona
Mary Jones 99982 25 Payson Arizona
Eric Edwards 88232 32 San Diego California
Mary Ann Edwards 88233 32 Phoenix Arizona
Ginger Howell 98002 42 Cottonwood Arizona
Sebastian Smith 92001 23 Gila Bend Arizona
Gus Gray 22322 35 Bagdad Arizona
Mary Ann May 32326 52 Tucson Arizona
Erica Williams 32327 60 Show Low Arizona
Leroy Brown 32380 22 Pinetop Arizona
Elroy Cleaver 32382 22 Globe Arizona

 

select first, last, city
from empinfo
where first LIKE 'Er%';

This SQL statement will match any first names that start with 'Er'. Strings must be in single quotes.

 

Or you can specify,

select first, last
from empinfo
where last LIKE '%s';

This statement will match any last names that end in a 's'.

select * from empinfo
where first = 'Eric';

This will only select rows where the first name equals 'Eric' exactly.

 

What will be the result of the following sample SELECT statements?

 

select first, last, city from empinfo; 

first last city
John Jones Payson
Mary Jones Payson
Eric Edwards San Diego
Mary Ann Edwards Phoenix
Ginger Howell Cottonwood
Sebastian Smith Gila Bend
Gus Gray Bagdad
Mary Ann May Tucson
Erica Williams Show Low
Leroy Brown Pinetop
Elroy Cleaver Globe
 

select last, city, age from empinfo 
where age > 30;

last city age
Jones Payson 45
Edwards San Diego 32
Edwards Phoenix 32
Howell Cottonwood 42
Gray Bagdad 35
May Tucson 52
Williams Show Low 60
 

 

select first, last, city, state from empinfo
       where first LIKE 'J%';

first last city state
John Jones Payson Arizona

 

select * from empinfo;

first last id age city state
John Jones 99980 45 Payson Arizona
Mary Jones 99982 25 Payson Arizona
Eric Edwards 88232 32 San Diego California
Mary Ann Edwards 88233 32 Phoenix Arizona
Ginger Howell 98002 42 Cottonwood Arizona
Sebastian Smith 92001 23 Gila Bend Arizona
Gus Gray 22322 35 Bagdad Arizona
Mary Ann May 32326 52 Tucson Arizona
Erica Williams 32327 60 Show Low Arizona
Leroy Brown 32380 22 Pinetop Arizona
Elroy Cleaver 32382 22 Globe Arizona

 

select first, last, from empinfo
       where last LIKE '%s'; 
 

first last
John Jones
Mary Jones
Eric Edwards
Mary Ann Edwards
Erica Williams

 

 select first, last, age from empinfo
       where last LIKE '%illia%';

first last age
Erica Williams 60

 

select * from empinfo where first = 'Eric'; 

first last id age city state
Eric Edwards 88232 32 San Diego California

 

 

Exercise 1.

Enter select statements to:

  1. Display the first name and age for everyone that's in the table.
  2. Display the first name, last name, and city for everyone that's not from Payson.
  3. Display all columns for everyone that is over 40 years old.
  4. Display the first and last names for everyone whose last name ends in an "ay".
  5. Display all columns for everyone whose first name equals "Mary".
  6. Display all columns for everyone whose first name contains "Mary".

Answers

 

Exercise 2.

items_ordered

customerid order_date item quantity price
10330 30-Jun-1999 Pogo stick 1 28.00
10101 30-Jun-1999 Raft 1 58.00
10298 01-Jul-1999 Skateboard 1 33.00
10101 01-Jul-1999 Life Vest 4 125.00
10299 06-Jul-1999 Parachute 1 1250.00
10339 27-Jul-1999 Umbrella 1 4.50
10449 13-Aug-1999 Unicycle 1 180.79
10439 14-Aug-1999 Ski Poles 2 25.50
10101 18-Aug-1999 Rain Coat 1 18.30
10449 01-Sep-1999 Snow Shoes 1 45.00
10439 18-Sep-1999 Tent 1 88.00
10298 19-Sep-1999 Lantern 2 29.00
10410 28-Oct-1999 Sleeping Bag 1 89.22
10438 01-Nov-1999 Umbrella 1 6.75
10438 02-Nov-1999 Pillow 1 8.50
10298 01-Dec-1999 Helmet 1 22.00
10449 15-Dec-1999 Bicycle 1 380.50
10449 22-Dec-1999 Canoe 1 280.00
10101 30-Dec-1999 Hoola Hoop 3 14.75
10330 01-Jan-2000 Flashlight 4 28.00
10101 02-Jan-2000 Lantern 1 16.00
10299 18-Jan-2000 Inflatable Mattress 1 38.00
10438 18-Jan-2000 Tent 1 79.99
10413 19-Jan-2000 Lawnchair 4 32.00
10410 30-Jan-2000 Unicycle 1 192.50
10315 2-Feb-2000 Compass 1 8.00
10449 29-Feb-2000 Flashlight 1 4.50
10101 08-Mar-2000 Sleeping Bag 2 88.70
10298 18-Mar-2000 Pocket Knife 1 22.38
10449 19-Mar-2000 Canoe paddle 2 40.00
10298 01-Apr-2000 Ear Muffs 1 12.50
10330 19-Apr-2000 Shovel 1 16.75

 

Enter select statements to:

  1. From the items_ordered table, select a list of all items purchased for customerid 10449. Display the customerid, item, and price for this customer.
  2. Select all columns from the items_ordered table for whoever purchased a Tent.
  3. Select the customerid, order_date, and item values from the items_ordered table for any items in the item column that start with the letter "S".
  4. Select the distinct items in the items_ordered table. In other words, display a listing of each of the unique items from the items_ordered table.
  5. Make up your own select statements and submit them.

Answers

 

 

Aggregate Functions

 

MIN returns the smallest value in a given column
MAX returns the largest value in a given column
SUM returns the sum of the numeric values in a given column
AVG returns the average value of a given column
COUNT returns the total number of values in a given column
COUNT(*) returns the number of rows in a table

 

Aggregate functions are used to compute against a "returned column of numeric data" from your SELECT statement. They basically summarize the results of a particular column of selected data. We are covering these here since they are required by the next topic, "GROUP BY". Although they are required for the "GROUP BY" clause, these functions can be used without the "GROUP BY" clause. For example:

SELECT AVG(salary)
FROM employee;

This statement will return a single result which contains the average value of everything returned in the salary column from the employee table.

Another example:

SELECT AVG(salary)
    FROM employee;
WHERE title = 'Programmer';

 This statement will return the average salary for all employees whose title is equal to 'Programmer'

 Example:

valueprice_apiece
110
1009
5008
10007

 

 

Example:

SELECT Count(*)
FROM employees;

This particular statement is slightly different from the other aggregate functions since there isn't a column supplied to the count function. This statement will return the number of rows in the employees table.

 

 

Exercise 3.

  1. Select the maximum price of any item ordered in the items_ordered table ( see above ). Hint: Select the maximum price only.>
  2. Select the average price of all of the items ordered that were purchased in the month of Dec.
  3. What are the total number of rows in the items_ordered table?
  4. For all of the tents that were ordered in the items_ordered table, what is the price of the lowest tent? Hint: Your query should return the price only.

Answers

 

 

GROUP BY clause

 

The GROUP BY clause will gather all of the rows together that contain data in the specified column(s) and will allow aggregate functions to be performed on the one or more columns. This can best be explained by an example:

GROUP BY clause syntax:

SELECT column1, 
SUM(column2)
FROM "list-of-tables"
GROUP BY "column-list";

Let's say you would like to retrieve a list of the highest paid salaries in each dept:

SELECT max(salary), dept
FROM employee
GROUP BY dept;

This statement will select the maximum salary for the people in each unique department. Basically, the salary for the person who makes the most in each department will be displayed. Their, salary and their department will be returned.

 

What if I wanted to display their lastname too?

For example, take a look at the items_ordered table. Let's say you want to group everything of quantity 1 together, everything of quantity 2 together, everything of quantity 3 together, etc. If you would like to determine what the largest cost item is for each grouped quantity (all quantity 1's, all quantity 2's, all quantity 3's, etc.), you would enter:

SELECT quantity, max(price)
FROM items_ordered
GROUP BY quantity;

Enter the statement in above, and take a look at the results to see if it returned what you were expecting. Verify that the maximum price in each Quantity Group is really the maximum price.

 

Exercise 4.

customerid firstname lastname city state
10101 John Gray Lynden Washington
10298 Leroy Brown Pinetop Arizona
10299 Elroy Keller Snoqualmie Washington
10315 Lisa Jones Oshkosh Wisconsin
10325 Ginger Schultz Pocatello Idaho
10329 Kelly Mendoza Kailua Hawaii
10330 Shawn Dalton Cannon Beach Oregon
10338 Michael Howell Tillamook Oregon
10339 Anthony Sanchez Winslow Arizona
10408 Elroy Cleaver Globe Arizona
10410 Mary Ann Howell Charleston South Carolina
10413 Donald Davids Gila Bend Arizona
10419 Linda Sakahara Nogales Arizona
10429 Sarah Graham Greensboro North Carolina
10438 Kevin Smith Durango Colorado
10439 Conrad Giles Telluride Colorado
10449 Isabela Moore Yuma Arizona

 

  1. How many people are in each unique state in the customers table? Select the state and display the number of people in each. Hint: count is used to count rows in a column, sum works on numeric data only.
  2. From the items_ordered table, select the item, maximum price, and minimum price for each specific item in the table. Hint: The items will need to be broken up into separate groups.
  3. How many orders did each customer make? Use the items_ordered table. Select the customerid, number of orders they made, and the sum of their orders. Click the Group By answers link below if you have any problems.

Answers

 

 

HAVING clause

 

The HAVING clause allows you to specify conditions on the rows for each group - in other words, which rows should be selected will be based on the conditions you specify. The HAVING clause should follow the GROUP BY clause if you are going to use it.

HAVING clause syntax:

SELECT column1, 
SUM(column2)
FROM "list-of-tables"
GROUP BY "column-list"
HAVING "condition";

HAVING can best be described by example. Let's say you have an employee table containing the employee's name, department, salary, and age. If you would like to select the average salary for each employee in each department, you could enter:

SELECT dept, avg(salary)
FROM employee
GROUP BY dept;

But, let's say that you want to ONLY calculate & display the average if their salary is over 20000:

SELECT dept, avg(salary)
FROM employee
GROUP BY dept
HAVING avg(salary) > 20000;

 

Exercise 5.

  1. How many people are in each unique state in the customers table that have more than one person in the state? Select the state and display the number of how many people are in each if it's greater than 1.
  2. From the items_ordered table, select the item, maximum price, and minimum price for each specific item in the table. Only display the results if the maximum price for one of the items is greater than 190.00.
  3. How many orders did each customer make? Use the items_ordered table. Select the customerid, number of orders they made, and the sum of their orders if they purchased more than 1 item.

Answers

 

 

ORDER BY clause

 

ORDER BY is an optional clause which will allow you to display the results of your query in a sorted order (either ascending order or descending order) based on the columns that you specify to order by. 

 ORDER BY clause syntax:

SELECT column1, SUM(column2)
FROM "list-of-tables"
ORDER BY "column-list" [ASC | DESC];

[ ] = optional

This statement will select the employee_id, dept, name, age, and salary from the employee_info table where the dept equals 'Sales' and will list the results in Ascending (default) order based on their Salary.

ASC = Ascending Order - default
DESC = Descending Order


For example:

SELECT employee_id, dept, name, age, salary
FROM employee_info
WHERE dept = 'Sales'ORDER BY salary;

 

If you would like to order based on multiple columns, you must seperate the columns with commas. For example:

SELECT employee_id, dept, name, age, salary
FROM employee_info
WHERE dept = 'Sales'
ORDER BY salary, age DESC;

 

Exercise 6.

  1. Select the lastname, firstname, and city for all customers in the customers table. Display the results in Ascending Order based on the lastname.
  2. Same thing as exercise #1, but display the results in Descending order.
  3. Select the item and price for all of the items in the items_ordered table that the price is greater than 10.00. Display the results in Ascending order based on the price.

Answers

 

 

Combining conditions and Boolean Operators

 

The AND operator can be used to join two or more conditions in the WHERE clause. Both sides of the AND condition must be true in order for the condition to be met and for those rows to be displayed.

SELECT column1, 
SUM(column2)
FROM "list-of-tables"
WHERE "condition1" AND
"condition2";

The OR operator can be used to join two or more conditions in the WHERE clause also. However, either side of the OR operator can be true and the condition will be met - hence, the rows will be displayed. With the OR operator, either side can be true or both sides can be true.

For example:

SELECT employeeid, firstname, lastname, title, salary
FROM employee_info
WHERE salary >= 50000.00 AND title = 'Programmer';

 

This statement will select the employeeid, firstname, lastname, title, and salary from the employee_info table where the salary is greater than or equal to 50000.00 AND the title is equal to 'Programmer'. Both of these conditions must be true in order for the rows to be returned in the query. If either is false, then it will not be displayed.

Although they are not required, you can use paranthesis around your conditional expressions to make it easier to read:

SELECT employeeid, firstname, lastname, title, salary
FROM employee_info
WHERE (salary >= 50000.00) AND (title = 'Programmer');


Another Example:

SELECT firstname, lastname, title, salary
FROM employee_info
WHERE (title = 'Sales') OR (title = 'Programmer');

This statement will select the firstname, lastname, title, and salary from the employee_info table where the title is either equal to 'Sales' OR the title is equal to 'Programmer'.

 

Exercise 7.

  1. Select the customerid, order_date, and item from the items_ordered table for all items unless they are 'Snow Shoes' or if they are 'Ear Muffs'. Display the rows as long as they are not either of these two items.
  2. Select the item and price of all items that start with the letters 'S', 'P', or 'F'.

Answers

 

 

IN and BETWEEN Conditional Operators

 

SELECT col1, SUM(col2)
FROM "list-of-tables"
WHERE col3 IN
       (list-of-values);
SELECT col1, SUM(col2)
FROM "list-of-tables"
WHERE col3 BETWEEN value1
AND value2;

The IN conditional operator is really a set membership test operator. That is, it is used to test whether or not a value (stated before the keyword IN) is "in" the list of values provided after the keyword IN.

For example:

SELECT employeeid, lastname, salary
FROM employee_info
WHERE lastname IN ('Hernandez', 'Jones', 'Roberts', 'Ruiz');


This statement will select the employeeid, lastname, salary from the employee_info table where the lastname is equal to either: Hernandez, Jones, Roberts, or Ruiz. It will return the rows if it is ANY of these values.

The IN conditional operator can be rewritten by using compound conditions using the equals operator and combining it with OR - with exact same output results:

SELECT employeeid, lastname, salary
FROM employee_info
WHERE lastname = 'Hernandez' OR lastname = 'Jones'
OR lastname = 'Roberts'OR lastname = 'Ruiz';

As you can see, the IN operator is much shorter and easier to read when you are testing for more than two or three values.
You can also use NOT IN to exclude the rows in your list.

The BETWEEN conditional operator is used to test to see whether or not a value (stated before the keyword BETWEEN) is "between" the two values stated after the keyword BETWEEN.

For example:

SELECT employeeid, age, lastname, salary
FROM employee_info
WHERE age BETWEEN 30 AND 40;

This statement will select the employeeid, age, lastname, and salary from the employee_info table where the age is between 30 and 40 (including 30 and 40).

This statement can also be rewritten without the BETWEEN operator:

SELECT employeeid, age, lastname, salary
FROM employee_info
WHERE age >= 30 AND age <= 40;

You can also use NOT BETWEEN to exclude the values between your range.

 

Exercise 8.

  1. Select the date, item, and price from the items_ordered table for all of the rows that have a price value ranging from 10.00 to 80.00.
  2. Select the firstname, city, and state from the customers table for all of the rows where the state value is either: Arizona, Washington, Oklahoma, Colorado, or Hawaii.

Answers

 

 

Mathematical Operators

 

Standard ANSI SQL-92 supports the following first four basic arithmetic operators:

+ addition
- subtraction
* multiplication
/ division
% modulo

The modulo operator determines the integer remainder of the division. This operator is not ANSI SQL supported, however, most databases support it. The following are some more useful mathematical functions to be aware of since you might need them. These functions are not standard in the ANSI SQL-92 specs, therefore they may or may not be available on the specific RDBMS that you are using. However, they were available on several major database systems that I tested. They WILL work on this tutorial.

ABS(x) returns the absolute value of x
SIGN(x) returns the sign of input x as -1, 0, or 1 (negative, zero, or positive respectively)
MOD(x,y) modulo - returns the integer remainder of x divided by y (same as x%y)
FLOOR(x) returns the largest integer value that is less than or equal to x
CEILING(x) or CEIL(x) returns the smallest integer value that is greater than or equal to x
POWER(x,y) returns the value of x raised to the power of y
ROUND(x) returns the value of x rounded to the nearest whole integer
ROUND(x,d) returns the value of x rounded to the number of decimal places specified by the value d
SQRT(x) returns the square-root value of x

For example:

SELECT round(salary), firstname
FROM employee_info

This statement will select the salary rounded to the nearest whole value and the firstname from the employee_info table.

 

Exercise 9.

Select the item and per unit price for each item in the items_ordered table. Hint: Divide the price by the quantity.

Answer

 

 

Table Joins, a must

 

All of the queries up until this point have been useful with the exception of one major limitation - that is, you've been selecting from only one table at a time with your SELECT statement. It is time to introduce you to one of the most beneficial features of SQL & relational database systems - the "Join". To put it simply, the "Join" makes relational database systems "relational".

Joins allow you to link data from two or more tables together into a single query result--from one single SELECT statement.

A "Join" can be recognized in a SQL SELECT statement if it has more than one table after the FROM keyword.

For example:

SELECT "list-of-columns"
FROM table1,table2
WHERE "search-condition(s)"

Joins can be explained easier by demonstrating what would happen if you worked with one table only, and didn't have the ability to use "joins". This single table database is also sometimes referred to as a "flat table". Let's say you have a one-table database that is used to keep track of all of your customers and what they purchase from your store:

idfirst lastaddresscitystate zipdateitemprice

 

Everytime a new row is inserted into the table, all columns will be be updated, thus resulting in unnecessary "redundant data". For example, every time Wolfgang Schultz purchases something, the following rows will be inserted into the table:

idfirstlastaddress            citystatezipdateitemprice
10982WolfgangSchultz300 N. 1st AveYumaAZ85002032299snowboard45.00
10982WolfgangSchultz300 N. 1st AveYumaAZ85002082899snow shovel35.00
10982WolfgangSchultz300 N. 1st AveYumaAZ85002091199gloves15.00
10982WolfgangSchultz300 N. 1st AveYumaAZ85002100999lantern35.00
10982WolfgangSchultz300 N. 1st AveYumaAZ85002022900tent85.00

An ideal database would have two tables:

  1. One for keeping track of your customers
  2. And the other to keep track of what they purchase:

"Customer_info" table:

customer_numberfirstname lastnameaddresscitystate zip

"Purchases" table:

customer_numberdate itemprice

Now, whenever a purchase is made from a repeating customer, the 2nd table, "Purchases" only needs to be updated! We've just eliminated useless redundant data, that is, we've just normalized this database!

Notice how each of the tables have a common "cusomer_number" column. This column, which contains the unique customer number will be used to JOIN the two tables. Using the two new tables, let's say you would like to select the customer's name, and items they've purchased. Here is an example of a join statement to accomplish this:

SELECT customer_info.firstname, customer_info.lastname, purchases.item
FROM customer_info, purchases
WHERE customer_info.customer_number = purchases.customer_number;

This particular "Join" is known as an "Inner Join" or "Equijoin". This is the most common type of "Join" that you will see or use.

Notice that each of the colums are always preceeded with the table name and a period. This isn't always required, however, it IS good practice so that you wont confuse which colums go with what tables. It is required if the name column names are the same between the two tables. I recommend preceeding all of your columns with the table names when using joins.

Note: The syntax described above will work with most Database Systems -including the one with this tutorial. However, in the event that this doesn't work with yours, please check your specific database documentation.

Although the above will probably work, here is the ANSI SQL-92 syntax specification for an Inner Join using the preceding statement above that you might want to try:

SELECT customer_info.firstname, customer_info.lastname, purchases.item
FROM customer_info INNER JOIN purchases
ON customer_info.customer_number = purchases.customer_number;

SELECT customer_info.firstname, customer_info.lastname, purchases.item
FROM customer_info INNER JOIN purchases
ON customer_info.customer_number = purchases.customer_number;


Another example:

SELECT employee_info.employeeid, employee_info.lastname, employee_sales.comission
FROM employee_info, employee_sales
WHERE employee_info.employeeid = employee_sales.employeeid;
 

This statement will select the employeeid, lastname (from the employee_info table), and the comission value (from the employee_sales table) for all of the rows where the employeeid in the employee_info table matches the employeeid in the employee_sales table.

Exercises 10. 

  1. Write a query using a join to determine which items were ordered by each of the customers in the customers table. Select the customerid, firstname, lastname, order_date, item, and price for everything each customer purchased in the items_ordered table.
  2. Repeat exercise #1, however display the results sorted by state in descending order.
Answers

 

 

Creating Tables

The create table statement is used to create a new table. Here is the format of a simple create table statement:

create table "tablename"
("column1" "data type",
"column2" "data type",
"column3" "data type");

Format of create table if you were to use optional constraints:

create table "tablename"
("column1" "data type"
[constraint],
"column2" "data type"
[constraint],
"column3" "data type"
[constraint]);
[ ] = optional

Note: You may have as many columns as you'd like, and the constraints are optional.

 

Example:

create table employee
(first varchar(15),
last varchar(20),
age number(3),
address varchar(30),
city varchar(20),
state varchar(20));

 

To create a new table, enter the keywords create table followed by the table name, followed by an open parenthesis, followed by the first column name, followed by the data type for that column, followed by any optional constraints, and followed by a closing parenthesis. It is important to make sure you use an open parenthesis before the beginning table, and a closing parenthesis after the end of the last column definition. Make sure you seperate each column definition with a comma. All SQL statements should end with a ";".

The table and column names must start with a letter and can be followed by letters, numbers, or underscores - not to exceed a total of 30 characters in length. Do not use any SQL reserved keywords as names for tables or column names (such as "select", "create", "insert", etc).

Data types specify what the type of data can be for that particular column. If a column called "Last_Name", is to be used to hold names, then that particular column should have a "varchar" (variable-length character) data type.

Here are the most common Data types:

char(size)Fixed-length character string. Size is specified in parenthesis. Max 255 bytes.
varchar(size)Variable-length character string. Max size is specified in parenthesis.
number(size)Number value with a max number of column digits specified in parenthesis.
dateDate value
number(size,d)Number value with a maximum number of digits of "size" total, with a maximum number of "d" digits to the right of the decimal.

What are constraints? When tables are created, it is common for one or more columns to have constraints associated with them. A constraint is basically a rule associated with a column that the data entered into that column must follow. For example, a "unique" constraint specifies that no two records can have the same value in a particular column. They must all be unique. The other two most popular constraints are "not null" which specifies that a column can't be left blank, and "primary key". A "primary key" constraint defines a unique identification of each record (or row) in a table. All of these and more will be covered in the future Advanced release of this Tutorial. Constraints can be entered in this SQL interpreter, however, they are not supported in this Intro to SQL tutorial & interpreter. They will be covered and supported in the future release of the Advanced SQL tutorial - that is, if "response" is good.

It's now time for you to design and create your own table. You will use this table throughout the rest of the tutorial. If you decide to change or redesign the table, you can either drop it and recreate it or you can create a completely different one. The SQL statement drop will be covered later.

 

Exercise 11. 

You have just started a new company. It is time to hire some employees. You will need to create a table that will contain the following information about your new employees: firstname, lastname, title, age, and salary. 

Answer

 

 

Inserting into a Table

The insert statement is used to insert or add a row of data into the table.

To insert records into a table, enter the key words insert into followed by the table name, followed by an open parenthesis, followed by a list of column names separated by commas, followed by a closing parenthesis, followed by the keyword values, followed by the list of values enclosed in parenthesis. The values that you enter will be held in the rows and they will match up with the column names that you specify. Strings should be enclosed in single quotes, and numbers should not.

insert into "tablename"
(first_column,...last_column)
values (first_value,...last_value);

 

In the example below, the column name first will match up with the value 'Luke', and the column name state will match up with the value 'Georgia'.

Example:

insert into employee
(first, last, age, address, city, state)
values ('Luke', 'Duke', 45, '2130 Boars Nest',
'Hazard Co', 'Georgia');

 

Note: All strings should be enclosed between single quotes: 'string'

 

Exercise 12. 

It is time to insert data into your new employee table.

Your first three employees are the following:

Jonie Weber, Secretary, 28, 19500.00
Potsy Weber, Programmer, 32, 45300.00
Dirk Smith, Programmer II, 45, 75020.00

Enter these employees into your table first, and then insert at least 5 more of your own list of employees in the table.

After they're inserted into the table, enter select statements to:

  1. Select all columns for everyone in your employee table.
  2. Select all columns for everyone with a salary over 30000.
  3. Select first and last names for everyone that's under 30 years old.
  4. Select first name, last name, and salary for anyone with "Programmer" in their title.
  5. Select all columns for everyone whose last name contains "ebe".
  6. Select the first name for everyone whose first name equals "Potsy".
  7. Select all columns for everyone over 80 years old.
  8. Select all columns for everyone whose last name ends in "ith".

 

Answers

 

 

Updating Records

The update statement is used to update or change records that match a specified criteria. This is accomplished by carefully constructing a where clause.

update "tablename"
set "columnname" =
"newvalue"
[,"nextcolumn" =
"newvalue2"...]
where "columnname"
OPERATOR "value"
[and|or "column"
OPERATOR "value"];

[] = optional

 [The above example was line wrapped for better viewing on this Web page.]

 

Examples:

update phone_book
set area_code = 623
where prefix = 979;

update phone_book
set last_name = 'Smith', prefix=555, suffix=9292
where last_name = 'Jones';

update employee
set age = age+1
where first_name='Mary' and last_name='Williams';

 

Exercise 13.

After each update, issue a select statement to verify your changes.

  1. Jonie Weber just got married to Bob Williams. She has requested that her last name be updated to Weber-Williams.
  2. Dirk Smith's birthday is today, add 1 to his age.
  3. All secretaries are now called "Administrative Assistant". Update all titles accordingly.
  4. Everyone that's making under 30000 are to receive a 3500 a year raise.
  5. Everyone that's making over 33500 are to receive a 4500 a year raise.
  6. All "Programmer II" titles are now promoted to "Programmer III".
  7. All "Programmer" titles are now promoted to "Programmer II".

Answers

 

 

Deleting Records

The delete statement is used to delete records or rows from the table.

delete from "tablename"

where "columnname"
OPERATOR "value"
[and|or "column"
OPERATOR "value"];

[ ] = optional

[The above example was line wrapped for better viewing on this Web page.]

Examples:

delete from employee;

 Note: if you leave off the where clause, all records will be deleted!

 

delete from employee
where lastname = 'May';

delete from employee
where firstname = 'Mike' or firstname = 'Eric';


To delete an entire record/row from a table, enter "delete from" followed by the table name, followed by the where clause which contains the conditions to delete. If you leave off the where clause, all records will be deleted.

 

Exercise 14.

(Use the select statement to verify your deletes):

  1. Jonie Weber-Williams just quit, remove her record from the table.
  2. It's time for budget cuts. Remove all employees who are making over 70000 dollars.

Answers

 

 

Drop a Table

The drop table command is used to delete a table and all rows in the table.

To delete an entire table including all of its rows, issue the drop table command followed by the tablename. drop table is different from deleting all of the records in the table. Deleting all of the records in the table leaves the table including column and constraint information. Dropping the table removes the table definition as well as all of its rows.

drop table "tablename"

 

Example:

drop table myemployees_ts0211;

 
 

Exercise 15.

Drop your employee table.

 

 

 

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based on http://sqlcourse2.com/