PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Retrieving Data from the Database
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The same output, however, produced by this join query:
select customerid, amount
from orders
order by amount desc
limit 1;
Because it relies on LIMIT, this query is not compatible with most RDBMSs, but it executes
more efficiently on MySQL than the subquery version.
One of the main reasons that MySQL did not get subqueries for so long was that
there is very little that you cannot do without them.Technically, you can create a single,
legal ANSI SQL query that has the same effect but relies on an inefficient, hack
approach called the MAX-CONCAT trick.
You can use subquery values in this way with all the normal comparison operators.
Some special subquery comparison operators are also available, detailed in the next
section.
Subqueries and Operators
There are five special subquery operators. Four are used with regular subqueries, and one
(EXISTS) is usually used only with correlated subqueries and is covered in the next section.The
four regular subquery operators are shown in Table 10.4.
Table 10.4 Subquery Operators
Name Sample Syntax Description
ANY SELECT c1 FROM t1 Returns true if the comparison is
WHERE c1 >
true for any of the rows in the subquery.
ANY (SELECT c1 FROM t2);
IN SELECT c1 FROM t1 Equivalent to =ANY.
WHERE c1 IN
(SELECT c1 from t2);
SOME SELECT c1 FROM t1 Alias for ANY; sometimes reads better
WHERE c1 >
to the human ear
SOME (SELECT c1 FROM t2);!
ALL SELECT c1 FROM t1 Returns true if the comparison is
WHERE c1 >
true for all of the rows in the subquery.
ALL (SELECT c1 from t2);
Each of these operators can appear only after a comparison operator, except for IN,
which has its comparison operator (=) “rolled in,” so to speak.