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This article is based on Create statement, which is used to create a database:
CREATE DATABASE database_name
Create a Table: To create a table in a database
CREATE TABLE table_name
(
column_name1 data_type,
column_name2 data_type,
.......
)
Example 1:
This example demonstrates how you can create a table named "Person", with four columns. The column names will be "LastName", "FirstName", "Address", and "Age":
CREATE TABLE Person
(
LastName varchar,
FirstName varchar,
Address varchar,
Age int
)
This example demonstrates how you can specify a maximum length for some columns:
CREATE TABLE Person
(
LastName varchar(30),
FirstName varchar,
Address varchar,
Age int(3)
)
The data type specifies what type of data the column can hold. The table below contains the most common data types in SQL:
DATA TYPE DESCRIPTION
integer(size)
int(size)
smallint(size)
tinyint(size) Hold integers only. The maximum number of digits are specified in parenthesis.
decimal(size,d)
numeric(size,d) 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".
char(size) Holds a fixed length string (can contain letters, numbers, and special characters). The fixed size is specified in parenthesis.
varchar(size) Holds a variable length string (can contain letters, numbers, and special characters). The maximum size is specified in parenthesis.
date(yyyymmdd) Holds a date.
Create Index
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.
Remember: 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.
A Unique Index
Creates a unique index on a table. A unique index means that two rows cannot have the same index value.
CREATE UNIQUE INDEX index_name
ON table_name (column_name)
The "column_name" specifies the column you want indexed.
A Simple Index
Creates a simple index on a table. When the UNIQUE keyword is omitted, duplicate values are allowed.
CREATE INDEX index_name
ON table_name (column_name)
The "column_name" specifies the column you want indexed.
Example 2: This example creates a simple index, named "PersonIndex", on the LastName field of the Person table:
CREATE INDEX PersonIndex
ON Person (LastName)
If you want to index the values in a column in descending order, you can add the reserved word DESC after the column name:
CREATE INDEX PersonIndex
ON Person (LastName DESC)
If you want to index more than one column you can list the column names within the parentheses, separated by commas:
CREATE INDEX PersonIndex
ON Person (LastName, FirstName)
