sql server - SELECT - SQL vs T-SQL? -

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my book says

there’s interesting difference between standard sql , t-sql in terms of minimal >select query requirements. according standard sql, select query must have @ minimum , select clauses. conversely, t-sql supports select query select clause , without clause. such query if issued against imaginary table has 1 row. example, following query invalid according standard sql valid according t-sql.

select 10 col1, 'abc' col2;  col1    col2 10      abc

how feature possibly useful ?

not data coming database might database/table. perhaps want metadata, or server-side variable:

select @server_side_variable;

other dbs around restriction having virtual table named dual, have from clause, doesn't point @ 'real' table in database:

select @server_side_variable dual;

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