SQL Basic
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SQL Select
SQL Distinct
SQL Where
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SQL Order By
SQL Insert
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SQL Delete
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SQL Full Join
SQL Union
SQL Select Into
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SQL Create Table
SQL Constraints
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SQL Create Index
SQL Drop
SQL Alter
SQL Increment
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SQL Nulls
SQL isnull()
SQL Data Types
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SQL FunctionsSQL avg()
SQL count()
SQL first()
SQL last()
SQL max()
SQL min()
SQL sum()
SQL Group By
SQL Having
SQL ucase()
SQL lcase()
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SQL len()
SQL round()
SQL now()
SQL format()
SQL Quick Ref
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SQL Summary
SQL Quiz
SQL QuizSQL CREATE INDEX Statement
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The CREATE INDEX statement is used to create indexes in tables.
Indexes allow the database application to find data fast; without reading the whole table.
Indexes
An index can be created in a table to find data more quickly and efficiently.
The users cannot see the indexes, they are just used to speed up searches/queries.
Note: Updating a table with indexes takes more time than updating a table without (because the indexes also need an update). So you should only create indexes on columns (and tables) that will be frequently searched against.
SQL CREATE INDEX Syntax
Creates an index on a table. Duplicate values are allowed:
| CREATE INDEX index_name ON table_name (column_name) |
SQL CREATE UNIQUE INDEX Syntax
Creates a unique index on a table. Duplicate values are not allowed:
| CREATE UNIQUE INDEX index_name ON table_name (column_name) |
Note: The syntax for creating indexes varies amongst different databases. Therefore: Check the syntax for creating indexes in your database.
CREATE INDEX Example
The SQL statement below creates an index named "PIndex" on the "LastName" column in the "Persons" table:
| CREATE INDEX PIndex ON Persons (LastName) |
If you want to create an index on a combination of columns, you can list the column names within the parentheses, separated by commas:
| CREATE INDEX PIndex ON Persons (LastName, FirstName) |
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