Flash cards
Review the key moves
What is the main idea behind SQL INDEX Keyword?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___ INDEX idx_lastnamePut the learning moves in the order that makes the concept easiest to apply.
Create Index
The CREATE INDEX command is used to create indexes in tables (allows duplicate values).
Indexes are used to retrieve data from the database very fast. The users cannot see the indexes, they are just used to speed up searches/queries.
The following SQL creates an index named "idx_lastname" on the "LastName" column in the "Persons" table:
CREATE INDEX idx_lastname
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 idx_pname
ON Persons (LastName, FirstName);Note
The syntax for creating indexes varies among different databases. Therefore: Check the syntax for creating indexes in your database.
Note
Updating a table with indexes takes more time than updating a table without (because the indexes also need an update). So, only create indexes on columns that will be frequently searched against.
Drop Index
The DROP INDEX command is used to delete an index in a table.
MS Access
DROP INDEX
index_name
ON
table_name
;SQL Server
DROP INDEX
table_name
.
index_name
;DB2/Oracle
DROP INDEX
index_name
;MySQL
ALTER TABLE
table_name
DROP INDEX
index_name
;