What's the purpose of SQL keyword “AS”?

Question

You can set table aliases in SQL typing the identifier right after the table name.

SELECT * FROM table t1;

You can even use the keyword AS to indicate the alias.

SELECT * FROM table AS t1;

What's the difference between them if any?

I see old DBA people tend to write statements without AS, but most of the new tutorials use it.

Update: I know what's the purpose of table and column aliases. I'm curious, what's the reason for having a separate keyword for setting aliases while it works without it as well.

Answer 1

You can use either of the SQL queries and both serve the same purpose in this case. I recommend using AS operator and it is a good practice to use. AS operator is used to give another name to the table or column in the database. 

Suppose, if you want to reduce the discount of 100 from product_cost.

SELECT (product_cost -100) as Discount 

FROM product_table 

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