Joins in LINQ to SQL on more than one column

How do you make a join on several columns between two tables in LINQ to SQL. As I learned from LINQ in the beginning was that it worked with only one column and that is of course a limitation. But there is two ways to make a join on more than one column in LINQ to SQL.

First a example with a join between two tables on one column:
var result = from F in context.FirstTables
join S in context.SecondTables on F.ColumnA equals S.ColumnD
select new
{
F.ColumnA,
F.ColumnB,
F.ColumnC,
S.ColumnD,
S.ColumnE,
S.ColumnF
};

The SQL generated:
SELECT [t0].[ColumnA], [t0].[ColumnB], [t0].[ColumnC], [t1].[ColumnD], [t1].ColumnE], [t1].[ColumnF]
FROM [dbo].[FirstTable] AS [t0]
INNER JOIN [dbo].[SecondTable] AS [t1] ON [t0].[ColumnA] = [t1].[ColumnD]

The first example on a join on more than one column is to write the join as a where clause. That is an old way of writing SQL queries.
var result = from F in context.FirstTables
join S in context.SecondTables on F.ColumnA equals S.ColumnD
where F.ColumnB == S.ColumnE
select new
{
F.ColumnA,
F.ColumnB,
F.ColumnC,
S.ColumnD,
S.ColumnE,
S.ColumnF
};

The SQL generated:
SELECT [t0].[ColumnA], [t0].[ColumnB], [t0].[ColumnC], [t1].[ColumnD], [t1].ColumnE], [t1].[ColumnF]
FROM [dbo].[FirstTable] AS [t0]
INNER JOIN [dbo].[SecondTable] AS [t1] ON [t0].[ColumnA] = [t1].[ColumnD]
WHERE [t0].[ColumnB] = [t1].[ColumnE]

If there is many joins it’s hard to see which one is a join and what is actually belonging to the question. So there is a better way to write the join on more than one column. Write the join a comparison on two anonymous data types.
var result = from F in context.FirstTables
join S in context.SecondTables
on new { ID = F.ColumnA, Col = F.ColumnB } equals new { ID = S.ColumnD, Col = S.ColumnE }
select new
{
F.ColumnA,
F.ColumnB,
F.ColumnC,
S.ColumnD,
S.ColumnE,
S.ColumnF
};

The SQL generated:
SELECT [t1].[ColumnA] AS [ColumnA], [t1].[ColumnB] AS [ColumnB], [t1].[ColumnC] AS [ColumnC], [t2].[ColumnD], [t2].[ColumnE], [t2].[ColumnF]
FROM ( SELECT NULL AS [EMPTY] ) AS [t0]
LEFT OUTER JOIN [dbo].[FirstTable] AS [t1] ON 1=1
INNER JOIN [dbo].[SecondTable] AS [t2] ON ([t1].[ColumnA] = [t2].[ColumnD]) AND ([t1].[ColumnB] = [t2].[ColumnE])

All joins in LINQ to SQL is inner joins if you don’t specify a left or right join. Next example is a left join between FirstTable and the SecondTable
var result = from F in context.FirstTables.DefaultIfEmpty()
join S in context.SecondTables
on new { ID = F.ColumnA, Col = F.ColumnB } equals new { ID = S.ColumnD, Col = S.ColumnE }
select new
{
F.ColumnA,
F.ColumnB,
F.ColumnC,
S.ColumnD,
S.ColumnE,
S.ColumnF
};

The SQL generated:
SELECT [t1].[ColumnA] AS [ColumnA], [t1].[ColumnB] AS [ColumnB], [t1].[ColumnC] AS [ColumnC], [t2].[ColumnD], [t2].[ColumnE], [t2].[ColumnF]
FROM ( SELECT NULL AS [EMPTY] ) AS [t0]
LEFT OUTER JOIN [dbo].[FirstTable] AS [t1] ON 1=1
INNER JOIN [dbo].[SecondTable] AS [t2] ON ([t1].[ColumnA] = [t2].[ColumnD]) AND ([t1].[ColumnB] = [t2].[ColumnE])