Snippets below have been condensed from their original sources for brevity. See references for original articles.

Great reference on joins: http://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins

Show all tables in specific database: (MSSQL equivalent of MySql “show tables”)

select name from <database name>..sysobjects where xtype = 'U'

Insert into:

INSERT INTO MusicArtists (FirstName, LastName, Instrument)
VALUES ('Bobby', 'Lee', 'fiddle');

INSERT INTO Duos (Member1) 
    SELECT FirstName + ' ' + LastName FROM MusicArtists;

INSERT INTO Duos (Member1) 
    SELECT FirstName + ' ' + LastName FROM MusicArtists 
    WHERE MusicianID > 3;

INSERT INTO Residents (Name, Occupation)
    SELECT Name, Occupation FROM Immigration 
    WHERE Residency = 'granted';

INSERT INTO Insurance (Name) 
    SELECT Employee.Username FROM Employee 
    INNER JOIN Project ON Employee.EmployeeID = Project.EmployeeID 
    WHERE Project.ProjectName = 'Hardwork';

Insert if not exists:

IF NOT EXISTS (SELECT * FROM dbo.Applications WHERE Username = Tom ANDApplication = Calculator) BEGIN
 INSERT INTO dbo.Applications 
 (Date, Username, Application, Version) 
 VALUES
 ('3/10/2009', 'Tom', 'Calculator', '2.0') 
END

Trigger Syntax Structure:

CREATE TRIGGER trigger_name 
ON { table | view } 
[ WITH ENCRYPTION ] 
{ 
{ { FOR | AFTER | INSTEAD OF } { [ INSERT ] [ , ] [ UPDATE ] [ , ] [ DELETE ] } 
[ WITH APPEND ] 
[ NOT FOR REPLICATION ] 
AS 
[ { IF UPDATE ( column ) 
[ { AND | OR } UPDATE ( column ) ] 
[ ...n ] 
| IF ( COLUMNS_UPDATED ( ) { bitwise_operator } updated_bitmask ) 
{ comparison_operator } column_bitmask [ ...n ] 
} ] 
sql_statement [ ...n ] 
} 
} 

Basic If, Then , Else and case:

--longer
create proc sp_generic (@cust int, @type int)
if @type = 1
 select * from customer where customerid = @cust
else
 Select * from deleted_customers where customerid = @cust

--shorter
create proc sp_generic (@deptid int )
select * from employees where departmentid = case when @dept >0 then @dept else departmentid end
order by departmentid

Insert Trigger:

CREATE TRIGGER trig_addAuthor 

ON authors 

FOR INSERT 

AS

-- Get the first and last name of new author 

DECLARE @newName VARCHAR(100) 

SELECT @newName = (SELECT au_fName + ' ' + au_lName FROM Inserted)

-- Print the name of the new author 

PRINT 'New author "' + @newName + '" added.'

Update Trigger:

USE AdventureWorks2008R2;
GO
IF EXISTS (SELECT name FROM sys.objects
      WHERE name = 'reminder' AND type = 'TR')
   DROP TRIGGER Person.reminder;
GO
CREATE TRIGGER reminder
ON Person.Address
AFTER UPDATE 
AS 
IF ( UPDATE (StateProvinceID) OR UPDATE (PostalCode) )
BEGIN
RAISERROR (50009, 16, 10)
END;
GO
-- Test the trigger.
UPDATE Person.Address
SET PostalCode = 99999
WHERE PostalCode = '12345';
GO

Get and/or compare today’s date:

convert(varchar,CURRENT_TIMESTAMP,101)
convert(varchar(12),getdate(),101)

Insert or Update with case statements:

USE [mydatabasename]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[sp_update_manufacturedrobots_count]
	@mfgid int,
	@robotid int,
	@paintbotcount int=null,
	@drillbotcount int=null,
	@hammerbotcount int=null
AS
BEGIN

	SET NOCOUNT ON;

declare @id int
select @id = id from manufacturedrobots where mfgid=@mfgid and robotid=@robotid
if @id is not null
update manufacturedrobots set 
paintbotcount=case
when @paintbotcount is null then paintbotcount 
else @paintbotcount end, 
favorite=case
when @drillbotcount is null then drillbotcount 
else @drillbotcount end, 
checkedin=case
when @hammerbotcount is null then hammerbotcount 
else @hammerbotcount end
where id=@id
else
insert into manufacturedrobots (paintbotcount,drillbotcount,hammerbotcount) values  (@paintbotcount,@drillbotcount,@hammerbotcount)

END

Cursor:

USE AdventureWorks
GO
DECLARE @ProductID INT
DECLARE @getProductID CURSOR
SET @getProductID = CURSOR FOR
SELECT ProductID
FROM Production.Product
OPEN @getProductID
FETCH NEXT
FROM @getProductID INTO @ProductID
WHILE @@FETCH_STATUS = 0
BEGIN
PRINT @ProductID
FETCH NEXT
FROM @getProductID INTO @ProductID
END
CLOSE @getProductID
DEALLOCATE @getProductID
GO

References:
MSDN, http://msdn.microsoft.com/en-us/library/ms187326.aspx
DevGuru, http://www.devguru.com/technologies/t-sql/7124.asp
DevArticleshttp://www.devarticles.com/c/a/SQL-Server/Using-Triggers-In-MS-SQL-Server/1/
MSDN, “How to debug stored procedures in Visual Studio .NET”, http://support.microsoft.com/kb/316549
CodeGuru, http://www.codeguru.com/forum/showthread.php?t=473102
DaniWeb, http://www.daniweb.com/forums/thread43719.html
SqlAuthority, http://blog.sqlauthority.com/2008/03/05/sql-server-simple-example-of-cursor-sample-cursor-part-2/