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<h1>SQL Create Database, Table, and Index</h1>
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<hr />
<h2>Create a Database</h2>
<p>To create a database:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE DATABASE database_name</pre>
</td></tr></table>
<br />
<hr />
<h2>Create a Table</h2>
<p>To create a table in a database:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE TABLE table_name<i>
</i>(
column_name1 data_type,<i>
</i>column_name2 data_type,<i>
.......</i>
)</pre>
</td></tr></table>
<h3>Example</h3>
<p>This example demonstrates how you can create a table named
"Person", with four columns. The column names will be
"LastName",
"FirstName", "Address", and
"Age":</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE TABLE Person
(
LastName varchar,
FirstName varchar,
Address varchar,
Age int
)</pre></td></tr></table>
<p>This example demonstrates how you can specify a maximum length for some
columns:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE TABLE Person
(
LastName varchar(30),
FirstName varchar,
Address varchar,
Age int(3)
)</pre></td></tr></table>
<p>The data type specifies what type of data the column can hold. The table
below contains the most common data types in SQL:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<th width="30%" valign="top" align="left">Data Type</th>
<th width="70%" valign="top" align="left">Description</th>
</tr>
<tr>
<td valign="top">integer(size)<br />
int(size)<br />
smallint(size)<br />
tinyint(size)</td>
<td valign="top">Hold integers only. The maximum number of digits are specified in
parenthesis.</td>
</tr>
<tr>
<td valign="top">decimal(size,d)<br />
numeric(size,d)</td>
<td valign="top">Hold numbers with fractions. The maximum number of digits are specified in
"size". The maximum number of digits to the right of the decimal is
specified in "d".</td>
</tr>
<tr>
<td valign="top">char(size)</td>
<td valign="top"> Holds a fixed length string (can contain letters, numbers, and special
characters). The fixed size is specified in parenthesis.</td>
</tr>
<tr>
<td valign="top">varchar(size)</td>
<td valign="top">Holds a variable length string (can contain letters, numbers, and special
characters). The maximum size is specified in parenthesis.</td>
</tr>
<tr>
<td valign="top">date(yyyymmdd)</td>
<td valign="top">Holds a date</td>
</tr>
</table>
<br />
<hr />
<h2>Create Index</h2>
<p>Indices are created in an existing table to locate rows more quickly and
efficiently. It is possible to create an index on one or more columns of a
table, and each index is given a name. The users cannot see the indexes, they
are just used to speed up queries. </p>
<b>Note:</b> Updating a table containing indexes takes more time than updating
a table without, this is because the indexes also need an update. So, it
is a good idea to create indexes only on columns that are often used for a
search.<p><b>A Unique Index</b></p>
<p>Creates a unique index on a table. A unique index means that two rows cannot have the same index
value.</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE UNIQUE INDEX index_name
ON table_name (column_name)</pre>
</td></tr></table>
<p>The "column_name" specifies the column you want indexed.</p>
<p><b>A Simple Index</b></p>
<p>Creates a simple index on a table. When the UNIQUE keyword is omitted, duplicate values are allowed.</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE INDEX index_name
ON table_name (column_name)</pre>
</td></tr></table>
<p>The "column_name" specifies the column you want indexed.</p>
<h3>Example</h3>
<p>This example creates a simple index, named "PersonIndex", on the
LastName field of the Person table:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE INDEX PersonIndex
ON Person (LastName)</pre>
</td></tr></table>
<p>If you want to index the values in a column in <b>descending</b> order, you
can add the reserved word <b>DESC</b> after the column name:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE INDEX PersonIndex
ON Person (LastName DESC)</pre>
</td></tr></table>
<p>If you want to index more than one column you can list the column names
within the parentheses, separated by commas:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td><pre>CREATE INDEX PersonIndex
ON Person (LastName, FirstName)</pre>
</td></tr></table>
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