Select

Syntax:

Select * | {Distinct} column | expression [alias] ,... }  from table;

Select all Columns : Select * from table_name;

Selecting particular column:   Select column1,column2 from table_name;

Examples:
Select last_name,salary+300 from table_name
Select last_name, 12*salary+300 from table_name
Select last_name,12*(salary+100) from table_name


Arthritic Expression

Alias
Select last_name as name from table_name (alias)
Select last_name “Name” from table_name

Concatitation: 
Select first_name||last_name from table_name
Select last_name||'is a'|| salary from table_name (literal)
Select last_name || q'[, it's a manager_id]' from table_name

Distinct: Unique
Select distinct(last_name) from table_name

SQL comparison Operators

=	Equal  (a = b )
!=  or  <>	Not Equal ( a != b)
<	Less than
>	Greater than
<=	Less than equal to
>=	Greater than equal to
any	Compares one value with any value in list
all	Compares one value with all values in list
like	Matches patterns in strings. _ single character , % multiple
in	Matches lists of values
between	Matches range of values
Is null	Matches null values
Is nan	Matches nan special value, not number
Is infinite	Matches binary float and binary infinite
and	Returns true when x and y are true
or	Returns true when either x or y is true
Not x	Return true if x is false , returns false if x is true