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from the set of result rows before it is returned. ^For the purposes of
detecting duplicate rows, two NULL values are considered to be equal. ^The
normal rules for selecting a collation sequence to compare text values with
apply.

<h3>Compound Select Statements</h3>

<p>Two or more simple SELECT statements may be connected together to form
a compound SELECT using the UNION, UNION ALL, INTERSECT or EXCEPT operator.
^In a compound SELECT, all the constituent SELECTs must return the same 
number of result columns. ^As the components of a compound SELECT must
be simple SELECT statements, they may not contain ORDER BY or LIMIT clauses.
^ORDER BY and LIMIT clauses may only occur at the end of the entire compound
SELECT.  

<p>^A compound SELECT created using UNION ALL operator returns all the rows
from the SELECT to the left of the UNION ALL operator, and all the rows
from the SELECT to the right of it. ^The UNION operator works the same way as
UNION ALL, except that duplicate rows are removed from the final result set.
^The INTERSECT operator returns the intersection of the results of the left and
right SELECTs.  ^The EXCEPT operator returns the subset of rows returned by the
left SELECT that are not also returned by the right-hand SELECT. ^Duplicate
rows are removed from the results of INTERSECT and EXCEPT operators before the
result set is returned.

<p>^For the purposes of determining duplicate rows for the results of compound
SELECT operators, NULL values are considered equal to other NULL values and
distinct from all non-NULL values. ^The collation sequences to compare text
values values are determined as if the columns of the left and right-hand
SELECT statements were the left and right-hand operands of the equals (=)
operator. ^No affinity transformations are applied to any values when 
comparing rows as part of a compound SELECT. 

<p>^(When three or more simple SELECTs are connected into a compound SELECT,
they group from left to right. In other words, if "A", "B" and "C" are all
simple SELECT statements, (A op B op C) is processed as ((A op B) op C).)^

</p>

<h3>ORDER BY and LIMIT/OFFSET Clauses</h3>

<p>^The ORDER BY clause causes the output rows to be sorted.  
^The argument to ORDER BY is a list of expressions that are used as the
key for the sort.  ^The expressions do not have to be part of the
result for a simple SELECT, but in a compound SELECT each sort