Basic SQL Tutorial

 
SQL Tutorial
 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.

SQL is a standard language for accessing and manipulating databases. 
·  SQL can execute queries against a database
·  SQL can retrieve data from a database
·  SQL can insert records in a database
·  SQL can update records in a database
·  SQL can delete records from a database
·  SQL can create new databases
·  SQL can create new tables in a database
·  SQL can create stored procedures in a database
·  SQL can create views in a database
·  SQL can set permissions on tables, procedures, and views 

SQL Syntax

Database Tables
A database most often contains one or more tables. Each table is identified by a name (e.g. "Customers" or "Orders"). Tables contain records (rows) with data.
Below is an example of a table called "Persons":
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
The table above contains three records (one for each person) and five columns (P_Id, LastName, FirstName, Address, and City).
SQL Statements
Most of the actions you need to perform on a database are done with SQL statements.
The following SQL statement will select all the records in the "Persons" table:
SELECT * FROM Persons
In this tutorial we will teach you all about the different SQL statements.
Keep in Mind That...
  • SQL is not case sensitive

Semicolon after SQL Statements?
Some database systems require a semicolon at the end of each SQL statement.
Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server.
We are using MS Access and SQL Server 2000 and we do not have to put a semicolon after each SQL statement, but some database programs force you to use it.
SQL DML and DDL
SQL can be divided into two parts: The Data Manipulation Language (DML) and the Data Definition Language (DDL).
The query and update commands form the DML part of SQL:
  • SELECT - extracts data from a database
  • UPDATE - updates data in a database
  • DELETE - deletes data from a database
  • INSERT INTO - inserts new data into a database
The DDL part of SQL permits database tables to be created or deleted. It also defines indexes (keys), specifies links between tables, and imposes constraints between tables. The most important DDL statements in SQL are:
  • CREATE DATABASE - creates a new database
  • ALTER DATABASE - modifies a database
  • CREATE TABLE - creates a new table
  • ALTER TABLE - modifies a table
  • DROP TABLE - deletes a table
  • CREATE INDEX - creates an index (search key)
    DROP INDEX - deletes an index

The SQL SELECT Statement
The SELECT statement is used to select data from a database.
The result is stored in a result table, called the result-set.
SQL SELECT Syntax
SELECT column_name(s)
FROM table_name
and
SELECT * FROM table_name
 Note: SQL is not case sensitive. SELECT is the same as select.
An SQL SELECT Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Now we want to select the content of the columns named "LastName" and "FirstName" from the table above.
We use the following SELECT statement:
SELECT LastName,FirstName FROM Persons
The result-set will look like this:
LastName
FirstName
Hansen
Ola
Svendson
Tove
Pettersen
Kari

SELECT * Example
Now we want to select all the columns from the "Persons" table.
We use the following SELECT statement: 
SELECT * FROM Persons
Tip: The asterisk (*) is a quick way of selecting all columns!
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger

Navigation in a Result-set
Most database software systems allow navigation in the result-set with programming functions, like: Move-To-First-Record, Get-Record-Content, Move-To-Next-Record, etc.


The SQL SELECT DISTINCT Statement
In a table, some of the columns may contain duplicate values. This is not a problem, however, sometimes you will want to list only the different (distinct) values in a table.
The DISTINCT keyword can be used to return only distinct (different) values.
SQL SELECT DISTINCT Syntax
SELECT DISTINCT column_name(s)
FROM table_name

SELECT DISTINCT Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Now we want to select only the distinct values from the column named "City" from the table above.
We use the following SELECT statement:
SELECT DISTINCT City FROM Persons
The result-set will look like this:
City
Sandnes
Stavanger

 The WHERE Clause 
The WHERE clause is used to extract only those records that fulfill a specified criterion.
SQL WHERE Syntax
SELECT column_name(s)
FROM table_name
WHERE column_name operator value

WHERE Clause Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Now we want to select only the persons living in the city "Sandnes" from the table above.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE City='Sandnes'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes



Quotes Around Text Fields
SQL uses single quotes around text values (most database systems will also accept double quotes).
However, numeric values should not be enclosed in quotes.
For text values:
This is correct:

SELECT * FROM Persons WHERE FirstName='Tove'

This is wrong:

SELECT * FROM Persons WHERE FirstName=Tove
For numeric values:
This is correct:

SELECT * FROM Persons WHERE Year=1965

This is wrong:

SELECT * FROM Persons WHERE Year='1965'

Operators Allowed in the WHERE Clause
With the WHERE clause, the following operators can be used:
Operator
Description
=
Equal
<> 
Not equal
Greater than
Less than
>=
Greater than or equal
<=
Less than or equal
BETWEEN
Between an inclusive range
LIKE
Search for a pattern
IN
To specify multiple possible values for a column
Note: In some versions of SQL the <> operator may be written as !=


The AND & OR Operators
The AND operator displays a record if both the first condition and the second condition is true.
The OR operator displays a record if either the first condition or the second condition is true.
AND Operator Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Now we want to select only the persons with the first name equal to "Tove" AND the last name equal to "Svendson":
We use the following SELECT statement:
SELECT * FROM Persons
WHERE FirstName='Tove'
AND LastName='Svendson'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
2
Svendson
Tove
Borgvn 23
Sandnes

OR Operator Example
Now we want to select only the persons with the first name equal to "Tove" OR the first name equal to "Ola":
We use the following SELECT statement:
SELECT * FROM Persons
WHERE FirstName='Tove'
OR FirstName='Ola'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes

Combining AND & OR
You can also combine AND and OR (use parenthesis to form complex expressions).
Now we want to select only the persons with the last name equal to "Svendson" AND the first name equal to "Tove" OR to "Ola":
We use the following SELECT statement:
SELECT * FROM Persons WHERE
LastName='Svendson'
AND (FirstName='Tove' OR FirstName='Ola')
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
2
Svendson
Tove
Borgvn 23
Sandnes

The ORDER BY Keyword
The ORDER BY keyword is used to sort the result-set by a specified column.
The ORDER BY keyword sort the records in ascending order by default.
If you want to sort the records in a descending order, you can use the DESC keyword.
SQL ORDER BY Syntax
SELECT column_name(s)
FROM table_name
ORDER BY column_name(s) ASC|DESC

ORDER BY Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Tom
Vingvn 23
Stavanger
Now we want to select all the persons from the table above, however, we want to sort the persons by their last name.
We use the following SELECT statement:
SELECT * FROM Persons
ORDER BY LastName
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
4
Nilsen
Tom
Vingvn 23
Stavanger
3
Pettersen
Kari
Storgt 20
Stavanger
2
Svendson
Tove
Borgvn 23
Sandnes



ORDER BY DESC Example
Now we want to select all the persons from the table above, however, we want to sort the persons descending by their last name.
We use the following SELECT statement:
SELECT * FROM Persons
ORDER BY LastName DESC
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Tom
Vingvn 23
Stavanger
1
Hansen
Ola
Timoteivn 10
Sandnes
The INSERT INTO Statement
The INSERT INTO statement is used to insert a new row in a table.

SQL INSERT INTO Syntax
It is possible to write the INSERT INTO statement in two forms.
The first form doesn't specify the column names where the data will be inserted, only their values:
INSERT INTO table_name
VALUES (value1, value2, value3,...)
The second form specifies both the column names and the values to be inserted:
INSERT INTO table_name (column1, column2, column3,...)
VALUES (value1, value2, value3,...)

SQL INSERT INTO Example
We have the following "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Now we want to insert a new row in the "Persons" table.
We use the following SQL statement:
INSERT INTO Persons
VALUES (4,'Nilsen', 'Johan', 'Bakken 2', 'Stavanger')
The "Persons" table will now look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Johan
Bakken 2
Stavanger

Insert Data Only in Specified Columns
It is also possible to only add data in specific columns.
The following SQL statement will add a new row, but only add data in the "P_Id", "LastName" and the "FirstName" columns:
INSERT INTO Persons (P_Id, LastName, FirstName)
VALUES (5, 'Tjessem', 'Jakob')
The "Persons" table will now look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Johan
Bakken 2
Stavanger
5
Tjessem
Jakob



The UPDATE Statement
The UPDATE statement is used to update existing records in a table.
SQL UPDATE Syntax
UPDATE table_name
SET column1=value, column2=value2,...
WHERE some_column=some_value
Note: Notice the WHERE clause in the UPDATE syntax. The WHERE clause specifies which record or records that should be updated. If you omit the WHERE clause, all records will be updated!
SQL UPDATE Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Johan
Bakken 2
Stavanger
5
Tjessem
Jakob


Now we want to update the person "Tjessem, Jakob" in the "Persons" table.
We use the following SQL statement:
UPDATE Persons
SET Address='Nissestien 67', City='Sandnes'
WHERE LastName='Tjessem' AND FirstName='Jakob'
The "Persons" table will now look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Johan
Bakken 2
Stavanger
5
Tjessem
Jakob
Nissestien 67
Sandnes



SQL UPDATE Warning
Be careful when updating records. If we had omitted the WHERE clause in the example above, like this:
UPDATE Persons
SET Address='Nissestien 67', City='Sandnes'
The "Persons" table would have looked like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Nissestien 67
Sandnes
2
Svendson
Tove
Nissestien 67
Sandnes
3
Pettersen
Kari
Nissestien 67
Sandnes
4
Nilsen
Johan
Nissestien 67
Sandnes
5
Tjessem
Jakob
Nissestien 67
Sandnes

The DELETE Statement
The DELETE statement is used to delete rows in a table.
SQL DELETE Syntax
DELETE FROM table_name
WHERE some_column=some_value
Note: Notice the WHERE clause in the DELETE syntax. The WHERE clause specifies which record or records that should be deleted. If you omit the WHERE clause, all records will be deleted!


SQL DELETE Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Johan
Bakken 2
Stavanger
5
Tjessem
Jakob
Nissestien 67
Sandnes
Now we want to delete the person "Tjessem, Jakob" in the "Persons" table.
We use the following SQL statement:
DELETE FROM Persons
WHERE LastName='Tjessem' AND FirstName='Jakob'
The "Persons" table will now look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Johan
Bakken 2
Stavanger



Delete All Rows
It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:
DELETE FROM table_name
or
DELETE * FROM table_name
Note: Be very careful when deleting records. You cannot undo this statement!
The TOP Clause
The TOP clause is used to specify the number of records to return.
The TOP clause can be very useful on large tables with thousands of records. Returning a large number of records can impact on performance.
Note: Not all database systems support the TOP clause.
SQL Server Syntax
SELECT TOP number|percent column_name(s)
FROM table_name



SQL SELECT TOP Equivalent in MySQL and Oracle

MySQL Syntax

SELECT column_name(s)
FROM table_name
LIMIT number

Example

SELECT *
FROM Persons
LIMIT 5

Oracle Syntax

SELECT column_name(s)
FROM table_name
WHERE ROWNUM <= number

Example

SELECT *
FROM Persons
WHERE ROWNUM <=5



SQL TOP Example

The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Tom
Vingvn 23
Stavanger

Now we want to select only the two first records in the table above.
We use the following SELECT statement:
SELECT TOP 2 * FROM Persons
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes



SQL TOP PERCENT Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
4
Nilsen
Tom
Vingvn 23
Stavanger
Now we want to select only 50% of the records in the table above.
We use the following SELECT statement:
SELECT TOP 50 PERCENT * FROM Persons
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes

The LIKE Operator
The LIKE operator is used to search for a specified pattern in a column.
SQL LIKE Syntax
SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern

LIKE Operator Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Now we want to select the persons living in a city that starts with "s" from the table above.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE City LIKE 's%'
The "%" sign can be used to define wildcards (missing letters in the pattern) both before and after the pattern.
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Next, we want to select the persons living in a city that ends with an "s" from the "Persons" table.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE City LIKE '%s'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
Next, we want to select the persons living in a city that contains the pattern "tav" from the "Persons" table.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE City LIKE '%tav%'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
3
Pettersen
Kari
Storgt 20
Stavanger
It is also possible to select the persons living in a city that does NOT contain the pattern "tav" from the "Persons" table, by using the NOT keyword.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE City NOT LIKE '%tav%'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes

SQL Wildcards 
SQL wildcards can substitute for one or more characters when searching for data in a database.
SQL wildcards must be used with the SQL LIKE operator.
With SQL, the following wildcards can be used:
Wildcard
Description
%
A substitute for zero or more characters
_
A substitute for exactly one character
[charlist]
Any single character in charlist
[^charlist]
or
[!charlist]
Any single character not in charlist

SQL Wildcard Examples
We have the following "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger



Using the % Wildcard
Now we want to select the persons living in a city that starts with "sa" from the "Persons" table.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE City LIKE 'sa%'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
Next, we want to select the persons living in a city that contains the pattern "nes" from the "Persons" table.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE City LIKE '%nes%'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes



Using the _ Wildcard
Now we want to select the persons with a first name that starts with any character, followed by "la" from the "Persons" table.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE FirstName LIKE '_la'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
Next, we want to select the persons with a last name that starts with "S", followed by any character, followed by "end", followed by any character, followed by "on" from the "Persons" table.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE LastName LIKE 'S_end_on'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
2
Svendson
Tove
Borgvn 23
Sandnes

Using the [charlist] Wildcard
Now we want to select the persons with a last name that starts with "b" or "s" or "p" from the "Persons" table.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE LastName LIKE '[bsp]%'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Next, we want to select the persons with a last name that do not start with "b" or "s" or "p" from the "Persons" table.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE LastName LIKE '[!bsp]%'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes

The IN Operator
The IN operator allows you to specify multiple values in a WHERE clause.
SQL IN Syntax
SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1,value2,...)



IN SQL Operator Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Now we want to select the persons with a last name equal to "Hansen" or "Pettersen" from the table above.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE LastName IN ('Hansen','Pettersen')
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger

The SQL BETWEEN Operator
The BETWEEN operator selects a range of data between two values. The values can be numbers, text, or dates.
SQL BETWEEN Syntax
SELECT column_name(s)
FROM table_name
WHERE column_name
BETWEEN value1 AND value2

BETWEEN Operator Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Now we want to select the persons with a last name alphabetically between "Hansen" and "Pettersen" from the table above.
We use the following SELECT statement:
SELECT * FROM Persons
WHERE LastName
BETWEEN 'Hansen' AND 'Pettersen'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
Note: The BETWEEN operator is treated differently in different databases!
In some databases, persons with the LastName of "Hansen" or "Pettersen" will not be listed, because the BETWEEN operator only selects fields that are between and excluding the test values.
In other databases, persons with the LastName of "Hansen" or "Pettersen" will be listed, because the BETWEEN operator selects fields that are between and including the test values.
And in other databases, persons with the LastName of "Hansen" will be listed, but "Pettersen" will not be listed (like the example above), because the BETWEEN operator selects fields between the test values, including the first test value and excluding the last test value.
Therefore: Check how your database treats the BETWEEN operator.
Example 2
To display the persons outside the range in the previous example, use NOT BETWEEN:
SELECT * FROM Persons
WHERE LastName
NOT BETWEEN 'Hansen' AND 'Pettersen'
The result-set will look like this:
P_Id
LastName
FirstName
Address
City
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger

SQL Alias
You can give a table or a column another name by using an alias. This can be a good thing to do if you have very long or complex table names or column names.
An alias name could be anything, but usually it is short.
SQL Alias Syntax for Tables
SELECT column_name(s)
FROM table_name
AS alias_name
SQL Alias Syntax for Columns
SELECT column_name AS alias_name
FROM table_name

Alias Example
Assume we have a table called "Persons" and another table called "Product_Orders". We will give the table aliases of "p" and "po" respectively.
Now we want to list all the orders that "Ola Hansen" is responsible for.
We use the following SELECT statement:
SELECT po.OrderID, p.LastName, p.FirstName
FROM Persons AS p,
Product_Orders AS po
WHERE p.LastName='Hansen' AND p.FirstName='Ola'
The same SELECT statement without aliases:
SELECT Product_Orders.OrderID, Persons.LastName, Persons.FirstName
FROM Persons,
Product_Orders
WHERE Persons.LastName='Hansen' AND Persons.FirstName='Ola'
As you'll see from the two SELECT statements above; aliases can make queries easier to both write and to read.
SQL JOIN
The JOIN keyword is used in an SQL statement to query data from two or more tables, based on a relationship between certain columns in these tables.
Tables in a database are often related to each other with keys.
A primary key is a column (or a combination of columns) with a unique value for each row. Each primary key value must be unique within the table. The purpose is to bind data together, across tables, without repeating all of the data in every table.
Look at the "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
Note that the "P_Id" column is the primary key in the "Persons" table. This means that no two rows can have the same P_Id. The P_Id distinguishes two persons even if they have the same name.
Next, we have the "Orders" table:
O_Id
OrderNo
P_Id
1
77895
3
2
44678
3
3
22456
1
4
24562
1
5
34764
15
Note that the "O_Id" column is the primary key in the "Orders" table and that the "P_Id" column refers to the persons in the "Persons" table without using their names.
Notice that the relationship between the two tables above is the "P_Id" column.


Different SQL JOINs
Before we continue with examples, we will list the types of JOIN you can use, and the differences between them.
  • JOIN: Return rows when there is at least one match in both tables
  • LEFT JOIN: Return all rows from the left table, even if there are no matches in the right table
  • RIGHT JOIN: Return all rows from the right table, even if there are no matches in the left table
  • FULL JOIN: Return rows when there is a match in one of the tables
SQL INNER JOIN Keyword
The INNER JOIN keyword return rows when there is at least one match in both tables.
SQL INNER JOIN Syntax
SELECT column_name(s)
FROM table_name1
INNER JOIN table_name2
ON table_name1.column_name=table_name2.column_name
PS: INNER JOIN is the same as JOIN.


SQL INNER JOIN Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
The "Orders" table:
O_Id
OrderNo
P_Id
1
77895
3
2
44678
3
3
22456
1
4
24562
1
5
34764
15
Now we want to list all the persons with any orders.
We use the following SELECT statement:
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
INNER JOIN Orders
ON Persons.P_Id=Orders.P_Id
ORDER BY Persons.LastName
The result-set will look like this:
LastName
FirstName
OrderNo
Hansen
Ola
22456
Hansen
Ola
24562
Pettersen
Kari
77895
Pettersen
Kari
44678
The INNER JOIN keyword return rows when there is at least one match in both tables. If there are rows in "Persons" that do not have matches in "Orders", those rows will NOT be listed.
SQL LEFT JOIN Keyword
The LEFT JOIN keyword returns all rows from the left table (table_name1), even if there are no matches in the right table (table_name2).
SQL LEFT JOIN Syntax
SELECT column_name(s)
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name
PS: In some databases LEFT JOIN is called LEFT OUTER JOIN.


SQL LEFT JOIN Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
The "Orders" table:
O_Id
OrderNo
P_Id
1
77895
3
2
44678
3
3
22456
1
4
24562
1
5
34764
15
Now we want to list all the persons and their orders - if any, from the tables above.
We use the following SELECT statement:
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
LEFT JOIN Orders
ON Persons.P_Id=Orders.P_Id
ORDER BY Persons.LastName
The result-set will look like this:
LastName
FirstName
OrderNo
Hansen
Ola
22456
Hansen
Ola
24562
Pettersen
Kari
77895
Pettersen
Kari
44678
Svendson
Tove

The LEFT JOIN keyword returns all the rows from the left table (Persons), even if there are no matches in the right table (Orders).
SQL RIGHT JOIN Keyword
The RIGHT JOIN keyword returns all the rows from the right table (table_name2), even if there are no matches in the left table (table_name1).
SQL RIGHT JOIN Syntax
SELECT column_name(s)
FROM table_name1
RIGHT JOIN table_name2
ON table_name1.column_name=table_name2.column_name
PS: In some databases RIGHT JOIN is called RIGHT OUTER JOIN.


SQL RIGHT JOIN Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
The "Orders" table:
O_Id
OrderNo
P_Id
1
77895
3
2
44678
3
3
22456
1
4
24562
1
5
34764
15
Now we want to list all the orders with containing persons - if any, from the tables above.
We use the following SELECT statement:
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
RIGHT JOIN Orders
ON Persons.P_Id=Orders.P_Id
ORDER BY Persons.LastName
The result-set will look like this:
LastName
FirstName
OrderNo
Hansen
Ola
22456
Hansen
Ola
24562
Pettersen
Kari
77895
Pettersen
Kari
44678


34764
The RIGHT JOIN keyword returns all the rows from the right table (Orders), even if there are no matches in the left table (Persons).
SQL FULL JOIN Keyword
The FULL JOIN keyword return rows when there is a match in one of the tables.
SQL FULL JOIN Syntax
SELECT column_name(s)
FROM table_name1
FULL JOIN table_name2
ON table_name1.column_name=table_name2.column_name



SQL FULL JOIN Example
The "Persons" table:
P_Id
LastName
FirstName
Address
City
1
Hansen
Ola
Timoteivn 10
Sandnes
2
Svendson
Tove
Borgvn 23
Sandnes
3
Pettersen
Kari
Storgt 20
Stavanger
The "Orders" table:
O_Id
OrderNo
P_Id
1
77895
3
2
44678
3
3
22456
1
4
24562
1
5
34764
15
Now we want to list all the persons and their orders, and all the orders with their persons.
We use the following SELECT statement:
SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
FULL JOIN Orders
ON Persons.P_Id=Orders.P_Id
ORDER BY Persons.LastName
The result-set will look like this:
LastName
FirstName
OrderNo
Hansen
Ola
22456
Hansen
Ola
24562
Pettersen
Kari
77895
Pettersen
Kari
44678
Svendson
Tove



34764
The FULL JOIN keyword returns all the rows from the left table (Persons), and all the rows from the right table (Orders). If there are rows in "Persons" that do not have matches in "Orders", or if there are rows in "Orders" that do not have matches in "Persons", those rows will be listed as well.
The SQL UNION Operator
The UNION operator is used to combine the result-set of two or more SELECT statements.
Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also have similar data types. Also, the columns in each SELECT statement must be in the same order.
SQL UNION Syntax
SELECT column_name(s) FROM table_name1
UNION
SELECT column_name(s) FROM table_name2
Note: The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL.
SQL UNION ALL Syntax
SELECT column_name(s) FROM table_name1
UNION ALL
SELECT column_name(s) FROM table_name2
PS: The column names in the result-set of a UNION are always equal to the column names in the first SELECT statement in the UNION.


SQL UNION Example
Look at the following tables:
"Employees_Norway":
E_ID
E_Name
01
Hansen, Ola
02
Svendson, Tove
03
Svendson, Stephen
04
Pettersen, Kari
"Employees_USA":
E_ID
E_Name
01
Turner, Sally
02
Kent, Clark
03
Svendson, Stephen
04
Scott, Stephen
Now we want to list all the different employees in Norway and USA.
We use the following SELECT statement:
SELECT E_Name FROM Employees_Norway
UNION
SELECT E_Name FROM Employees_USA
The result-set will look like this:
E_Name
Hansen, Ola
Svendson, Tove
Svendson, Stephen
Pettersen, Kari
Turner, Sally
Kent, Clark
Scott, Stephen
Note: This command cannot be used to list all employees in Norway and USA. In the example above we have two employees with equal names, and only one of them will be listed. The UNION command selects only distinct values.


SQL UNION ALL Example
Now we want to list all employees in Norway and USA:
SELECT E_Name FROM Employees_Norway
UNION ALL
SELECT E_Name FROM Employees_USA
Result
E_Name
Hansen, Ola
Svendson, Tove
Svendson, Stephen
Pettersen, Kari
Turner, Sally
Kent, Clark
Svendson, Stephen
Scott, Stephen

The SQL SELECT INTO Statement
The SELECT INTO statement selects data from one table and inserts it into a different table.
The SELECT INTO statement is most often used to create backup copies of tables.
SQL SELECT INTO Syntax
We can select all columns into the new table:
SELECT *
INTO new_table_name [IN externaldatabase]
FROM old_tablename
Or we can select only the columns we want into the new table:
SELECT column_name(s)
INTO new_table_name [IN externaldatabase]
FROM old_tablename

SQL SELECT INTO Example
Make a Backup Copy - Now we want to make an exact copy of the data in our "Persons" table.
We use the following SQL statement:
SELECT *
INTO Persons_Backup
FROM Persons
We can also use the IN clause to copy the table into another database:
SELECT *
INTO Persons_Backup IN 'Backup.mdb'
FROM Persons
We can also copy only a few fields into the new table:
SELECT LastName,FirstName
INTO Persons_Backup
FROM Persons

SQL SELECT INTO - With a WHERE Clause
We can also add a WHERE clause.
The following SQL statement creates a "Persons_Backup" table with only the persons who lives in the city "Sandnes":
SELECT LastName,Firstname
INTO Persons_Backup
FROM Persons
WHERE City='Sandnes'

SQL SELECT INTO - Joined Tables
Selecting data from more than one table is also possible.
The following example creates a "Persons_Order_Backup" table contains data from the two tables "Persons" and "Orders":
SELECT Persons.LastName,Orders.OrderNo
INTO Persons_Order_Backup
FROM Persons
INNER JOIN Orders
ON Persons.P_Id=Orders.P_Id

The CREATE DATABASE Statement
The CREATE DATABASE statement is used to create a database.
SQL CREATE DATABASE Syntax
CREATE DATABASE database_name

CREATE DATABASE Example
Now we want to create a database called "my_db".
We use the following CREATE DATABASE statement:

CREATE DATABASE my_db
Database tables can be added with the CREATE TABLE statement.
The CREATE TABLE Statement
The CREATE TABLE statement is used to create a table in a database.
SQL CREATE TABLE Syntax
CREATE TABLE table_name
(
column_name1 data_type,
column_name2 data_type,
column_name3 data_type,
....
)
The data type specifies what type of data the column can hold. For a complete reference of all the data types available in MS Access, MySQL, and SQL Server, go to our complete Data Types reference.
CREATE TABLE Example
Now we want to create a table called "Persons" that contains five columns: P_Id, LastName, FirstName, Address, and City.
We use the following CREATE TABLE statement:
CREATE TABLE Persons
(
P_Id int,
LastName varchar(255),
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
The P_Id column is of type int and will hold a number. The LastName, FirstName, Address, and City columns are of type varchar with a maximum length of 255 characters.
The empty "Persons" table will now look like this:
P_Id
LastName
FirstName
Address
City





The empty table can be filled with data with the INSERT INTO statement.
 

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