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#Mysql count rows in all tables how to
#Mysql count rows in all tables drivers
#Mysql count rows in all tables code

I didn't mention before that NULL in multiindexes is only available in MyISAM tables. We search on an index, using a pre-prepared statement handle with placeholders.

#Mysql count rows in all tables code

In fact I didn't exhibit any DBI code at all.įor frequent operations, we can improve performance with the sth->bind_params() method. I never said to use the error for program control. My point was to demonstrate the property of unique indexes which prevent duplication: a safety measure. I didn't believe in evil until I dated it. I don't know why, but I had to work around by doing the SQL myself :(Īlso, talking coding style, finding out if you can do something by seeing if it throws an error is probably a worse option than checking for it cleanly in the first place. At one point I had Tie::DBI crashing when it got an error from the POSTGRESQL database saying the the database couldn't insert a row. I created the table in a Sybase database, filled it with about 2500 rows with my db-stress tool and tested against it (with only 1000 iterations). Most RDBMS won't even consider using an index on a table with only 4 rows due to the overhead in I/O and processing.

#Mysql count rows in all tables how to

Re: Re: Re: How to count rows using DBI & mysql - Performance results So I think I am correct that there is an index by default on the leftmost column. In fact, not having indexes doesn't seem to make any difference (1230/sec vs. Only there are only 4 rows, so testing the remainder of the AND should be quick. It should be intelligent enough to only compare the second row if the first row succeeds. I believe that MySQL creates an index on the leftmost subset of columns anyway, due to the way it stores I hadn't thought of getting SQL to do the logic. Re: Re: How to count rows using DBI & mysql - Performance results Way4A 3077/s 184% 158% 155% 146% 146% 36% 34% 0% -Īn index on the columns in where clause might have a huge impact if you use count(*). Rate Way5A Way6A Way1A Way5B Wa圓A Way2B Way2A Way4B Way4A My $sql = "SELECT COUNT(*) FROM depend WHERE usedby='Depend::Module +' AND uses='DBI'" # Incorrect result, only checks first field # Fetch each row manually and do our own count My $sql = "SELECT usedby FROM depend WHERE usedby='Depend::Module' +AND uses='DBI'" My $sql = "SELECT uses FROM depend WHERE usedby='Depend::Module' AN +D uses='DBI'" My $sql = "SELECT * FROM depend WHERE usedby='Depend::Module'" My $sql = "SELECT uses FROM depend WHERE usedby='Depend::Module'" # Doesn't count second field in this routine #use strict # because of the sub references This would propagate back through the do() result.

#Mysql count rows in all tables drivers

To suggest that some drivers return -1 untill all rows are fetched.

Not sure whether the do() is portable.

I was less interested in the fact that some of the tests returned the 'wrong' result than the time taken, clearly in aįull solution you need the correct answer :-).

I don't know if there are any internal optimisations happening (i.e.

The DB was small enough to fit in memory, and machine had no load, no no disk accesses during tests.

(Tried - was quicker, but again, not DB pure)

Store "uses" relationship as a joined string in the module table and use PERLto manage.

(Not tried - Likely to be quicker, but less "pure" and some complexity in forward references.) be quicker, but at the expense of more lookup code and complication.)

Store IDs, rather than names in the DB.

In particular, I thought thatĭo() was just a wrapper round prepare/execute, so the time difference is

SELECT col1 is slightly faster than SELECT *.

Doesn't matter which column SELECT returns to do counting.

do() is more than twice as fast as prepare()/execute().using WHERE A='X' AND B='Y' is faster than WHERE A='X'.