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Getting Rows from a MySQL Table with max values?

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Top Forums Programming Getting Rows from a MySQL Table with max values?
# 8  
Old 05-04-2012
Quote:
Originally Posted by Corona688
It has to be something that, theoretically, can be done in a single pass.

It can find the highest value easily enough it needn't print anything until it's over. But to find all rows that match the highest value in one pass, it would need to be psychic -- it has to scan the entire table to figure out what the highest is. Once it's done that it's already printed all the results and can't start over.

Indexes and the like make searching and min/max a lot faster than brute-force table scans now, but they aren't used to make the database 'psychic' this way, because that'd mean inconsistent behavior.
So when I do the "having" clause it returns the first value on the list because it only scans the first element and then reads in this first value as being max -so "done"

Well, I guess code is code. If it works it doesn't have to be readable. Smilie
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MYSQLDUMPSLOW(1)					       MySQL Database System						  MYSQLDUMPSLOW(1)

NAME

       mysqldumpslow - Summarize slow query log files

SYNOPSIS

       mysqldumpslow [options] [log_file ...]

DESCRIPTION

       The MySQL slow query log contains information about queries that take a long time to execute (see Section 5.2.5, "The Slow Query Log").
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	   shell> mysqldumpslow [options] [log_file ...]

       mysqldumpslow supports the following options.

       o   --help

	   Display a help message and exit.

       o   -a

	   Do not abstract all numbers to N and strings to 'S'.

       o   --debug, -d

	   Run in debug mode.

       o   -g pattern

	   Consider only queries that match the (grep-style) pattern.

       o   -h host_name

	   Host name of MySQL server for *-slow.log file name. The value can contain a wildcare. The default is * (match all).

       o   -i name

	   Name of server instance (if using mysql.server startup script).

       o   -l

	   Do not subtract lock time from total time.

       o   -n N

	   Abstract numbers with at least N digits within names.

       o   -r

	   Reverse the sort order.

       o   -s sort_type

	   How to sort the output. The value of sort_type should be chosen from the following list:

	   o   t, at: Sort by query time or average query time

	   o   l, al: Sort by lock time or average lock time

	   o   s, as: Sort by rows sent or average rows sent

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	   Reading mysql slow query log from /usr/local/mysql/data/mysqld51-apple-slow.log
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	    insert into t2 select * from t1
	   Count: 3  Time=2.53s (7s)  Lock=0.00s (0s)  Rows=0.0 (0), root[root]@localhost
	    insert into t2 select * from t1 limit N
	   Count: 3  Time=2.13s (6s)  Lock=0.00s (0s)  Rows=0.0 (0), root[root]@localhost
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MySQL 5.1							    04/06/2010							  MYSQLDUMPSLOW(1)