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MS SQL Server Interview Question:
Is the PRIMARY KEY Column of a Table an Index in MS SQL Server?
Submitted by: AdministratorIf you define a primary key on a table, an index for the primary key column will be created by default. The tutorial exercise below shows you the index created as part of the primary key column of "ggl_links":
USE GlobalGuideLineDatabase;
GO
-- Drop the old table, if needed
DROP TABLE ggl_links;
GO
-- Create a table with primary key
CREATE TABLE ggl_links (
id INT PRIMARY KEY,
url VARCHAR(80) NOT NULL,
notes VARCHAR(1024),
counts INT,
created DATETIME NOT NULL DEFAULT(getdate())
);
GO
-- Create an index for column "url"
CREATE INDEX ggl_links_url ON ggl_links (url);
GO
-- View indexes
EXEC SP_HELP ggl_links;
GO
<pre>index_name index_description keys
----------------------- -------------------------- ----
ggl_links_url nonclustered located url
on PRIMARY
PK__ggl_links__239E4DCF clustered, unique, primary
key located on PRIMARY id
</pre>
Notice that the index created as part of the primary key is named by SQL Server as "PK__ggl_links__239E4DCF".
Submitted by: Administrator
USE GlobalGuideLineDatabase;
GO
-- Drop the old table, if needed
DROP TABLE ggl_links;
GO
-- Create a table with primary key
CREATE TABLE ggl_links (
id INT PRIMARY KEY,
url VARCHAR(80) NOT NULL,
notes VARCHAR(1024),
counts INT,
created DATETIME NOT NULL DEFAULT(getdate())
);
GO
-- Create an index for column "url"
CREATE INDEX ggl_links_url ON ggl_links (url);
GO
-- View indexes
EXEC SP_HELP ggl_links;
GO
<pre>index_name index_description keys
----------------------- -------------------------- ----
ggl_links_url nonclustered located url
on PRIMARY
PK__ggl_links__239E4DCF clustered, unique, primary
key located on PRIMARY id
</pre>
Notice that the index created as part of the primary key is named by SQL Server as "PK__ggl_links__239E4DCF".
Submitted by: Administrator
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