Adobe 38043740 - ColdFusion Standard - Mac Development Manual page 443

DEVELOPING COLDFUSION 9 APPLICATIONS
Accessing and Using Data
/* First statement. */
SELECT * FROM TableA
UNION ALL
(SELECT * FROM TableB
UNION
SELECT * FROM TableC
)
/* Second statement. */
(SELECT * FROM TableA
UNION ALL
SELECT * FROM TableB
)
UNION
SELECT * FROM TableC
In the first statement, there are no duplicates in the union between TableB and TableC. Then, in the union between
that set and TableA, the ALL keyword includes the duplicates. In the second statement, duplicates are included in the
union between TableA and TableB but are eliminated in the subsequent union with TableC. The ALL keyword has no
effect on the final result of this expression.
Using other keywords with UNION
When you perform a UNION, the individual SELECT statements cannot have their own ORDER BY or COMPUTE
clauses. You can only have one ORDER BY or COMPUTE clause after the last SELECT statement; this clause is applied
to the final, combined result set. You can only specify GROUP BY and HAVING expressions in the individual SELECT
statements.
Using conditional operators
Query of Queries lets you use the following conditional operators in your SQL statements:
Test conditional
This conditional tests whether a Boolean expression is True, False, or Unknown.
Syntax
cond_test ::= expression [IS [NOT] {TRUE | FALSE | UNKNOWN} ]
Example
SELECT _isValid FROM Chemicals
WHERE _isValid IS true;
Null conditional
This conditional tests whether an expression is null.
Syntax
null_cond ::= expression IS [NOT] NULL
Example
SELECT bloodVal FROM Standards
WHERE bloodVal IS NOT null;
Last updated 1/20/2012
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