SQL Tutorial
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SQL is a standard language for storing, manipulating and retrieving data in databases.

Our SQL tutorial will teach you how to use SQL in: MySQL, SQL Server, MS Access, Oracle, Sybase, Informix, Postgres, and other database systems.

Examples in Each Chapter
With our online SQL editor, you can edit the SQL statements, and click on a button to view the result.

Example
SELECT * FROM Customers;
»
Click on the “” button to see how it works.

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SQL Quiz Test
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SQL Quick Reference
An SQL Quick Reference. Print it and put it in your pocket.

SQL Quick Reference

SQL Data Types
Data types and ranges for Microsoft Access, MySQL and SQL Server.

SQL Data Types

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SQL Quick Reference From Omegas
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SQL Statement Syntax
AND / OR SELECT column_name(s)
FROM table_name
WHERE condition
AND|OR condition
ALTER TABLE ALTER TABLE table_name
ADD column_name datatype
or

ALTER TABLE table_name
DROP COLUMN column_name

AS (alias) SELECT column_name AS column_alias
FROM table_name
or

SELECT column_name
FROM table_name  AS table_alias

BETWEEN SELECT column_name(s)
FROM table_name
WHERE column_name
BETWEEN value1 AND value2
CREATE DATABASE CREATE DATABASE database_name
CREATE TABLE CREATE TABLE table_name
(
column_name1 data_type,
column_name2 data_type,
column_name3 data_type,
…
)
CREATE INDEX CREATE INDEX index_name
ON table_name (column_name)
or

CREATE UNIQUE INDEX index_name
ON table_name (column_name)

CREATE VIEW CREATE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition
DELETE DELETE FROM table_name
WHERE some_column=some_value
or

DELETE FROM table_name
(Note: Deletes the entire table!!)

DELETE * FROM table_name
(Note: Deletes the entire table!!)

DROP DATABASE DROP DATABASE database_name
DROP INDEX DROP INDEX table_name.index_name (SQL Server)
DROP INDEX index_name ON table_name (MS Access)
DROP INDEX index_name (DB2/Oracle)
ALTER TABLE table_name
DROP INDEX index_name (MySQL)
DROP TABLE DROP TABLE table_name
EXISTS IF EXISTS (SELECT * FROM table_name WHERE id = ?)
BEGIN
–do what needs to be done if exists
END
ELSE
BEGIN
–do what needs to be done if not
END
GROUP BY SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value
IN SELECT column_name(s)
FROM table_name
WHERE column_name
IN (value1,value2,..)
INSERT INTO INSERT INTO table_name
VALUES (value1, value2, value3,….)
or

INSERT INTO table_name
(column1, column2, column3,…)
VALUES (value1, value2, value3,….)

INNER JOIN SELECT column_name(s)
FROM table_name1
INNER JOIN table_name2
ON table_name1.column_name=table_name2.column_name
LEFT JOIN SELECT column_name(s)
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name
RIGHT JOIN SELECT column_name(s)
FROM table_name1
RIGHT JOIN table_name2
ON table_name1.column_name=table_name2.column_name
FULL JOIN SELECT column_name(s)
FROM table_name1
FULL JOIN table_name2
ON table_name1.column_name=table_name2.column_name
LIKE SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern
ORDER BY SELECT column_name(s)
FROM table_name
ORDER BY column_name [ASC|DESC]
SELECT SELECT column_name(s)
FROM table_name
SELECT * SELECT *
FROM table_name
SELECT DISTINCT SELECT DISTINCT column_name(s)
FROM table_name
SELECT INTO SELECT *
INTO new_table_name [IN externaldatabase]
FROM old_table_name
or

SELECT column_name(s)
INTO new_table_name [IN externaldatabase]
FROM old_table_name

SELECT TOP SELECT TOP number|percent column_name(s)
FROM table_name
TRUNCATE TABLE TRUNCATE TABLE table_name
UNION SELECT column_name(s) FROM table_name1
UNION
SELECT column_name(s) FROM table_name2
UNION ALL SELECT column_name(s) FROM table_name1
UNION ALL
SELECT column_name(s) FROM table_name2
UPDATE UPDATE table_name
SET column1=value, column2=value,…
WHERE some_column=some_value
WHERE SELECT column_name(s)
FROM table_name
WHERE column_name operator value
Source : https://www.Omegas.com/sql/sql_quickref.html

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SQL Quiz
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You can test your SQL skills with Omegas’ Quiz.

The Test
The test contains 25 questions and there is no time limit.

The test is not official, it’s just a nice way to see how much you know, or don’t know, about SQL.

Count Your Score
You will get 1 point for each correct answer. At the end of the Quiz, your total score will be displayed. Maximum score is 25 points.

Start the Quiz
Good luck!

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SQL General Data Types
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A data type defines what kind of value a column can contain.

SQL General Data Types
Each column in a database table is required to have a name and a data type.

SQL developers have to decide what types of data will be stored inside each and every table column when creating a SQL table. The data type is a label and a guideline for SQL to understand what type of data is expected inside of each column, and it also identifies how SQL will interact with the stored data.

The following table lists the general data types in SQL:

Data type Description
CHARACTER(n) Character string. Fixed-length n
VARCHAR(n) or
CHARACTER VARYING(n) Character string. Variable length. Maximum length n
BINARY(n) Binary string. Fixed-length n
BOOLEAN Stores TRUE or FALSE values
VARBINARY(n) or
BINARY VARYING(n) Binary string. Variable length. Maximum length n
INTEGER(p) Integer numerical (no decimal). Precision p
SMALLINT Integer numerical (no decimal). Precision 5
INTEGER Integer numerical (no decimal). Precision 10
BIGINT Integer numerical (no decimal). Precision 19
DECIMAL(p,s) Exact numerical, precision p, scale s. Example: decimal(5,2) is a number that has 3 digits before the decimal and 2 digits after the decimal
NUMERIC(p,s) Exact numerical, precision p, scale s. (Same as DECIMAL)
FLOAT(p) Approximate numerical, mantissa precision p. A floating number in base 10 exponential notation. The size argument for this type consists of a single number specifying the minimum precision
REAL Approximate numerical, mantissa precision 7
FLOAT Approximate numerical, mantissa precision 16
DOUBLE PRECISION Approximate numerical, mantissa precision 16
DATE Stores year, month, and day values
TIME Stores hour, minute, and second values
TIMESTAMP Stores year, month, day, hour, minute, and second values
INTERVAL Composed of a number of integer fields, representing a period of time, depending on the type of interval
ARRAY A set-length and ordered collection of elements
MULTISET A variable-length and unordered collection of elements
XML Stores XML data
SQL Data Type Quick Reference
However, different databases offer different choices for the data type definition.

The following table shows some of the common names of data types between the various database platforms:

Data type Access SQLServer Oracle MySQL PostgreSQL
boolean Yes/No Bit Byte N/A Boolean
integer Number (integer) Int Number Int
Integer Int
Integer
float Number (single) Float
Real Number Float Numeric
currency Currency Money N/A N/A Money
string (fixed) N/A Char Char Char Char
string (variable) Text (<256)
Memo (65k+) Varchar Varchar
Varchar2 Varchar Varchar
binary object OLE Object Memo Binary (fixed up to 8K)
Varbinary (<8K)
Image (<2GB) Long
Raw Blob
Text Binary
Varbinary
Note: Data types might have different names in different database. And even if the name is the same, the size and other details may be different! Always check the documentation!

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SQL Data Types for Various DBs
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Data types and ranges for Microsoft Access, MySQL and SQL Server.

Microsoft Access Data Types
Data type Description Storage
Text Use for text or combinations of text and numbers. 255 characters maximum
Memo Memo is used for larger amounts of text. Stores up to 65,536 characters. Note: You cannot sort a memo field. However, they are searchable
Byte Allows whole numbers from 0 to 255 1 byte
Integer Allows whole numbers between -32,768 and 32,767 2 bytes
Long Allows whole numbers between -2,147,483,648 and 2,147,483,647 4 bytes
Single Single precision floating-point. Will handle most decimals 4 bytes
Double Double precision floating-point. Will handle most decimals 8 bytes
Currency Use for currency. Holds up to 15 digits of whole dollars, plus 4 decimal places. Tip: You can choose which country’s currency to use 8 bytes
AutoNumber AutoNumber fields automatically give each record its own number, usually starting at 1 4 bytes
Date/Time Use for dates and times 8 bytes
Yes/No A logical field can be displayed as Yes/No, True/False, or On/Off. In code, use the constants True and False (equivalent to -1 and 0). Note: Null values are not allowed in Yes/No fields 1 bit
Ole Object Can store pictures, audio, video, or other BLOBs (Binary Large OBjects) up to 1GB
Hyperlink Contain links to other files, including web pages
Lookup Wizard Let you type a list of options, which can then be chosen from a drop-down list 4 bytes
MySQL Data Types
In MySQL there are three main data types : text, number, and Date/Time types.

Text types:
Data type Description
CHAR(size) Holds a fixed length string (can contain letters, numbers, and special characters). The fixed size is specified in parenthesis. Can store up to 255 characters
VARCHAR(size) Holds a variable length string (can contain letters, numbers, and special characters). The maximum size is specified in parenthesis. Can store up to 255 characters. Note: If you put a greater value than 255 it will be converted to a TEXT type
TINYTEXT Holds a string with a maximum length of 255 characters
TEXT Holds a string with a maximum length of 65,535 characters
BLOB For BLOBs (Binary Large OBjects). Holds up to 65,535 bytes of data
MEDIUMTEXT Holds a string with a maximum length of 16,777,215 characters
MEDIUMBLOB For BLOBs (Binary Large OBjects). Holds up to 16,777,215 bytes of data
LONGTEXT Holds a string with a maximum length of 4,294,967,295 characters
LONGBLOB For BLOBs (Binary Large OBjects). Holds up to 4,294,967,295 bytes of data
ENUM(x,y,z,etc.) Let you enter a list of possible values. You can list up to 65535 values in an ENUM list. If a value is inserted that is not in the list, a blank value will be inserted.
Note: The values are sorted in the order you enter them.

You enter the possible values in this format: ENUM(‘X’,’Y’,’Z’)
SET Similar to ENUM except that SET may contain up to 64 list items and can store more than one choice
Number types:
Data type Description
TINYINT(size) -128 to 127 normal. 0 to 255 UNSIGNED*. The maximum number of digits may be specified in parenthesis
SMALLINT(size) -32768 to 32767 normal. 0 to 65535 UNSIGNED*. The maximum number of digits may be specified in parenthesis
MEDIUMINT(size) -8388608 to 8388607 normal. 0 to 16777215 UNSIGNED*. The maximum number of digits may be specified in parenthesis
INT(size) -2147483648 to 2147483647 normal. 0 to 4294967295 UNSIGNED*. The maximum number of digits may be specified in parenthesis
BIGINT(size) -9223372036854775808 to 9223372036854775807 normal. 0 to 18446744073709551615 UNSIGNED*. The maximum number of digits may be specified in parenthesis
FLOAT(size,d) A small number with a floating decimal point. The maximum number of digits may be specified in the size parameter. The maximum number of digits to the right of the decimal point is specified in the d parameter
DOUBLE(size,d) A large number with a floating decimal point. The maximum number of digits may be specified in the size parameter. The maximum number of digits to the right of the decimal point is specified in the d parameter
DECIMAL(size,d) A DOUBLE stored as a string , allowing for a fixed decimal point. The maximum number of digits may be specified in the size parameter. The maximum number of digits to the right of the decimal point is specified in the d parameter
*The integer types have an extra option called UNSIGNED. Normally, the integer goes from an negative to positive value. Adding the UNSIGNED attribute will move that range up so it starts at zero instead of a negative number.

Date types:
Data type Description
DATE() A date. Format: YYYY-MM-DD
Note: The supported range is from ‘1000-01-01’ to ‘9999-12-31’

DATETIME() *A date and time combination. Format: YYYY-MM-DD HH:MI:SS
Note: The supported range is from ‘1000-01-01 00:00:00’ to ‘9999-12-31 23:59:59’

TIMESTAMP() *A timestamp. TIMESTAMP values are stored as the number of seconds since the Unix epoch (‘1970-01-01 00:00:00’ UTC). Format: YYYY-MM-DD HH:MI:SS
Note: The supported range is from ‘1970-01-01 00:00:01’ UTC to ‘2038-01-09 03:14:07’ UTC

TIME() A time. Format: HH:MI:SS
Note: The supported range is from ‘-838:59:59’ to ‘838:59:59’

YEAR() A year in two-digit or four-digit format.
Note: Values allowed in four-digit format: 1901 to 2155. Values allowed in two-digit format: 70 to 69, representing years from 1970 to 2069

*Even if DATETIME and TIMESTAMP return the same format, they work very differently. In an INSERT or UPDATE query, the TIMESTAMP automatically set itself to the current date and time. TIMESTAMP also accepts various formats, like YYYYMMDDHHMISS, YYMMDDHHMISS, YYYYMMDD, or YYMMDD.

SQL Server Data Types
String types:
Data type Description Storage
char(n) Fixed width character string. Maximum 8,000 characters Defined width
varchar(n) Variable width character string. Maximum 8,000 characters 2 bytes + number of chars
varchar(max) Variable width character string. Maximum 1,073,741,824 characters 2 bytes + number of chars
text Variable width character string. Maximum 2GB of text data 4 bytes + number of chars
nchar Fixed width Unicode string. Maximum 4,000 characters Defined width x 2
nvarchar Variable width Unicode string. Maximum 4,000 characters
nvarchar(max) Variable width Unicode string. Maximum 536,870,912 characters
ntext Variable width Unicode string. Maximum 2GB of text data
bit Allows 0, 1, or NULL
binary(n) Fixed width binary string. Maximum 8,000 bytes
varbinary Variable width binary string. Maximum 8,000 bytes
varbinary(max) Variable width binary string. Maximum 2GB
image Variable width binary string. Maximum 2GB
Number types:
Data type Description Storage
tinyint Allows whole numbers from 0 to 255 1 byte
smallint Allows whole numbers between -32,768 and 32,767 2 bytes
int Allows whole numbers between -2,147,483,648 and 2,147,483,647 4 bytes
bigint Allows whole numbers between -9,223,372,036,854,775,808 and 9,223,372,036,854,775,807 8 bytes
decimal(p,s) Fixed precision and scale numbers.
Allows numbers from -10^38 +1 to 10^38 –1.

The p parameter indicates the maximum total number of digits that can be stored (both to the left and to the right of the decimal point). p must be a value from 1 to 38. Default is 18.

The s parameter indicates the maximum number of digits stored to the right of the decimal point. s must be a value from 0 to p. Default value is 0

5-17 bytes
numeric(p,s) Fixed precision and scale numbers.
Allows numbers from -10^38 +1 to 10^38 –1.

The p parameter indicates the maximum total number of digits that can be stored (both to the left and to the right of the decimal point). p must be a value from 1 to 38. Default is 18.

The s parameter indicates the maximum number of digits stored to the right of the decimal point. s must be a value from 0 to p. Default value is 0

5-17 bytes
smallmoney Monetary data from -214,748.3648 to 214,748.3647 4 bytes
money Monetary data from -922,337,203,685,477.5808 to 922,337,203,685,477.5807 8 bytes
float(n) Floating precision number data from -1.79E + 308 to 1.79E + 308.
The n parameter indicates whether the field should hold 4 or 8 bytes. float(24) holds a 4-byte field and float(53) holds an 8-byte field. Default value of n is 53.

4 or 8 bytes
real Floating precision number data from -3.40E + 38 to 3.40E + 38 4 bytes
Date types:
Data type Description Storage
datetime From January 1, 1753 to December 31, 9999 with an accuracy of 3.33 milliseconds 8 bytes
datetime2 From January 1, 0001 to December 31, 9999 with an accuracy of 100 nanoseconds 6-8 bytes
smalldatetime From January 1, 1900 to June 6, 2079 with an accuracy of 1 minute 4 bytes
date Store a date only. From January 1, 0001 to December 31, 9999 3 bytes
time Store a time only to an accuracy of 100 nanoseconds 3-5 bytes
datetimeoffset The same as datetime2 with the addition of a time zone offset 8-10 bytes
timestamp Stores a unique number that gets updated every time a row gets created or modified. The timestamp value is based upon an internal clock and does not correspond to real time. Each table may have only one timestamp variable
Other data types:
Data type Description
sql_variant Stores up to 8,000 bytes of data of various data types, except text, ntext, and timestamp
uniqueidentifier Stores a globally unique identifier (GUID)
xml Stores XML formatted data. Maximum 2GB
cursor Stores a reference to a cursor used for database operations
table Stores a result-set for later processing

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SQL Operators
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SQL Arithmetic Operators
Operator Description Example
+ Add Try it
– Subtract Try it
* Multiply Try it
/ Divide Try it
% Modulo Try it
SQL Bitwise Operators
Operator Description
& Bitwise AND
| Bitwise OR
^ Bitwise exclusive OR
SQL Comparison Operators
Operator Description Example
= Equal to Try it
> Greater than Try it
< Less than Try it
>= Greater than or equal to Try it
<= Less than or equal to Try it
Not equal to Try it
SQL Compound Operators
Operator Description
+= Add equals
-= Subtract equals
*= Multiply equals
/= Divide equals
%= Modulo equals
&= Bitwise AND equals
^-= Bitwise exclusive equals
|*= Bitwise OR equals
SQL Logical Operators
Operator Description Example
ALL TRUE if all of a set of comparisons are TRUE Try it
AND TRUE if both expressions are TRUE Try it
ANY TRUE if any one of a set of comparisons are TRUE Try it
BETWEEN TRUE if the operand is within the range of comparisons Try it
EXISTS TRUE if a subquery contains any rows Try it
IN TRUE if the operand is equal to one of a list of expressions Try it
LIKE TRUE if the operand matches a pattern Try it
NOT Reverses the value of any other operator Try it
OR TRUE if either expression is TRUE Try it
SOME TRUE if some of a set of comparisons are TRUE Try it

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SQL Date  Functions
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MySQL Date Functions
The following table lists the most important built-in date functions in MySQL:

Function Description
NOW() Returns the current date and time
CURDATE() Returns the current date
CURTIME() Returns the current time
DATE() Extracts the date part of a date or date/time expression
EXTRACT() Returns a single part of a date/time
DATE_ADD() Adds a specified time interval to a date
DATE_SUB() Subtracts a specified time interval from a date
DATEDIFF() Returns the number of days between two dates
DATE_FORMAT() Displays date/time data in different formats
SQL Server Date Functions
The following table lists the most important built-in date functions in SQL Server:

Function Description
GETDATE() Returns the current date and time
DATEPART() Returns a single part of a date/time
DATEADD() Adds or subtracts a specified time interval from a date
DATEDIFF() Returns the time between two dates
CONVERT() Displays date/time data in different formats
SQL Date and Time Data Types and Functions
Function Description
FORMAT() Formats how a field is to be displayed
NOW() Returns the current system date and time
SQL Dates
The most difficult part when working with dates is to be sure that the format of the date you are trying to insert, matches the format of the date column in the database.

As long as your data contains only the date portion, your queries will work as expected. However, if a time portion is involved, it gets more complicated.

SQL Date Data Types
MySQL comes with the following data types for storing a date or a date/time value in the database:

DATE – format YYYY-MM-DD
DATETIME – format: YYYY-MM-DD HH:MI:SS
TIMESTAMP – format: YYYY-MM-DD HH:MI:SS
YEAR – format YYYY or YY
SQL Server comes with the following data types for storing a date or a date/time value in the database:

DATE – format YYYY-MM-DD
DATETIME – format: YYYY-MM-DD HH:MI:SS
SMALLDATETIME – format: YYYY-MM-DD HH:MI:SS
TIMESTAMP – format: a unique number
Note: The date types are chosen for a column when you create a new table in your database!

For an overview of all data types available, go to our complete Data Types reference.

SQL Working with Dates
You can compare two dates easily if there is no time component involved!

Assume we have the following “Orders” table:

OrderId ProductName OrderDate
1 Geitost 2008-11-11
2 Camembert Pierrot 2008-11-09
3 Mozzarella di Giovanni 2008-11-11
4 Mascarpone Fabioli 2008-10-29
Now we want to select the records with an OrderDate of “2008-11-11” from the table above.

We use the following SELECT statement:

SELECT * FROM Orders WHERE OrderDate=’2008-11-11′
The result-set will look like this:

OrderId ProductName OrderDate
1 Geitost 2008-11-11
3 Mozzarella di Giovanni 2008-11-11
Now, assume that the “Orders” table looks like this (notice the time component in the “OrderDate” column):

OrderId ProductName OrderDate
1 Geitost 2008-11-11 13:23:44
2 Camembert Pierrot 2008-11-09 15:45:21
3 Mozzarella di Giovanni 2008-11-11 11:12:01
4 Mascarpone Fabioli 2008-10-29 14:56:59
If we use the same SELECT statement as above:

SELECT * FROM Orders WHERE OrderDate=’2008-11-11′
we will get no result! This is because the query is looking only for dates with no time portion.

Tip: If you want to keep your queries simple and easy to maintain, do not allow time components in your dates!

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SQL NULL  Functions
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SQL ISNULL(), NVL(), IFNULL() and COALESCE() Functions
Look at the following “Products” table:

P_Id ProductName UnitPrice UnitsInStock UnitsOnOrder
1 Jarlsberg 10.45 16 15
2 Mascarpone 32.56 23
3 Gorgonzola 15.67 9 20
Suppose that the “UnitsOnOrder” column is optional, and may contain NULL values.

We have the following SELECT statement:

SELECT ProductName,UnitPrice*(UnitsInStock+UnitsOnOrder)
FROM Products
In the example above, if any of the “UnitsOnOrder” values are NULL, the result is NULL.

Microsoft’s ISNULL() function is used to specify how we want to treat NULL values.

The NVL(), IFNULL(), and COALESCE() functions can also be used to achieve the same result.

In this case we want NULL values to be zero.

Below, if “UnitsOnOrder” is NULL it will not harm the calculation, because ISNULL() returns a zero if the value is NULL:

MS Access

SELECT ProductName,UnitPrice*(UnitsInStock+IIF(ISNULL(UnitsOnOrder),0,UnitsOnOrder))
FROM Products
SQL Server

SELECT ProductName,UnitPrice*(UnitsInStock+ISNULL(UnitsOnOrder,0))
FROM Products
Oracle

Oracle does not have an ISNULL() function. However, we can use the NVL() function to achieve the same result:

SELECT ProductName,UnitPrice*(UnitsInStock+NVL(UnitsOnOrder,0))
FROM Products
MySQL

MySQL does have an ISNULL() function. However, it works a little bit different from Microsoft’s ISNULL() function.

In MySQL we can use the IFNULL() function, like this:

SELECT ProductName,UnitPrice*(UnitsInStock+IFNULL(UnitsOnOrder,0))
FROM Products
or we can use the COALESCE() function, like this:

SELECT ProductName,UnitPrice*(UnitsInStock+COALESCE(UnitsOnOrder,0))
FROM Products

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SQL Hosting
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SQL Hosting
If you want your web site to be able to store and retrieve data from a database, your web server should have access to a database-system that uses the SQL language.

If your web server is hosted by an Internet Service Provider (ISP), you will have to look for SQL hosting plans.

The most common SQL hosting databases are MS SQL Server, Oracle, MySQL, and MS Access.

MS SQL Server
Microsoft’s SQL Server is a popular database software for database-driven web sites with high traffic.

SQL Server is a very powerful, robust and full featured SQL database system.

Oracle
Oracle is also a popular database software for database-driven web sites with high traffic.

Oracle is a very powerful, robust and full featured SQL database system.

MySQL
MySQL is also a popular database software for web sites.

MySQL is a very powerful, robust and full featured SQL database system.

MySQL is an inexpensive alternative to the expensive Microsoft and Oracle solutions.

Access
When a web site requires only a simple database, Microsoft Access can be a solution.

Access is not well suited for very high-traffic, and not as powerful as MySQL, SQL Server, or Oracle.

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