SQL join syntax, when do you use "AS"?

I am working on an SQL statement and just wanted to clarify my understanding of join syntax in MS SQL.

Say I have the SQL...

select t.year from HOUSE AS h 
LEFT OUTER JOIN SUBJECT K 
    ON H.Name = K.Name 
INNER JOIN TESTCASE AS T 
    ON k.year IS NO开发者_JAVA技巧T NULL

Sorry for the confusing example but basically - why am I able to use LEFT OUTER JOIN SUBJECT K without the keyword AS whereas with an INNER JOIN, I need to use a keyword of AS for INNER JOIN TESTCASE AS T?

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'AS' is not required in either of these cases, but I prefer it personally from the point of view of readability, as it conveys exactly what you were meaning to do.

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As far as I know the AS is only for easy coding. You can create a smaller or more clear name for the table. So House as H and further in the query you can use H.Name instead of typing House.Name

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I believe 'AS' used to be a required keyword, but is no longer needed, only for readability. I find 'As' is often used when creating a name for a data item in the SELECT, but not when giving a name to a table in a JOIN. For example:

SELECT t.ID as TestID FROM [House] h JOIN [TestCase] t ON t.ID=h.TestID

I think this is probably because a set of data items displayed with no 'As' could become confusing as to how many items there are, and how many are just names applied to them.

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interesting though where the AS keyword is useful... lets say two tables have name and you get this back from a query in code then it is cool to change the column name to something unique.