i have this tabel,
CREATE TABLE `forum_rank` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) NOT NULL DEFAULT '0',
`rank` int(11) NOT NULL DEFAULT '0',
`forum_id` int(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;
now i ask about what perfome best, its * or alle felt like this 2 eg.
select * form forum_rank;
or
select id, user_id, rank, forum_id from forum_rank;
You should explicitly specify the columns. Otherwise the database engine will first have to find out what the table's columns are (resolve the * operator) and after perform the actual query.
I don't think performance will be a problem here. There's a better reason to prefer the second idiom: your code is less likely to break if you add additional columns.
Related
I'm working on a SQL table that save money transaction for every day. this is my table design:
CREATE TABLE `transaction` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`date` datetime NOT NULL,
`member_id` int(11) NOT NULL,
`name` varchar(60) CHARACTER SET utf8 DEFAULT NULL,
`balance_lastMonth` int(11) NOT NULL,
`income` int(11) NOT NULL,
`outcome` int(11) NOT NULL,
`balance` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `member_id` (`member_id`),
CONSTRAINT `transaction_ibfk_1` FOREIGN KEY (`member_id`) REFERENCES `member` (`id`)
) ENGINE=InnoDB CHARSET=latin1
the balance field formula : balance_lastMonth + income - outcome
and balance_lastMonth is balance in the last month
is it possible to achieve it in one table? if yes how to do it? or may be there is better way to do it. i'm using 10.4.6-MariaDB.
You can calculate the balance using a query:
select t.*,
sum(income - outcome) over (partition by member_id order by date) as balance,
sum(income - outcome) over (partition by member_id order by date) - (income - outcome) as balance_lastmonth
from transaction t;
The simplest thing to do is to encapsulate this in a view and just use that.
If you actually want to store the results in the table, you'll need to use a trigger. I don't recommend that approach unless you have some sort of requirement that the balances be stored.
I have two only records in a database table and I want to delete only one of them.
The problem is that I don't have any primary key nor unique identifier, so how could I delete one and only one record?
It seems a easy question but I didn't find out how to do it ¿?.
CREATE TABLE `ToDo` (
`id` bigint(20) NOT NULL,
`caption` varchar(255) DEFAULT NULL,
`description` varchar(255) DEFAULT NULL,
`priority` int(11) DEFAULT NULL,
`done` tinyint(1) DEFAULT NULL,
`idUser_c` int(11) DEFAULT NULL,
`idUser_u` int(11) DEFAULT NULL,
`idUser_d` int(11) DEFAULT NULL,
`date_c` datetime DEFAULT NULL,
`date_u` datetime DEFAULT NULL,
`date_d` datetime DEFAULT NULL,
`version` bigint(20) DEFAULT '0'
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `ToDo` (`id`,`caption`,`description`,`priority`,`done`,`idUser_c`,`idUser_u`,`idUser_d`,`date_c`,`date_u`,`date_d`,`version`) VALUES (3,'hello','how are you',2,0,1,1,1,'2018-03-03 13:35:54','2018-03-03 13:35:57','2018-03-03 13:36:00',0);
INSERT INTO `ToDo` (`id`,`caption`,`description`,`priority`,`done`,`idUser_c`,`idUser_u`,`idUser_d`,`date_c`,`date_u`,`date_d`,`version`) VALUES (3,'hello','how are you',2,0,1,1,1,'2018-03-03 13:35:54','2018-03-03 13:35:57','2018-03-03 13:36:00',0);
This addresses the title, which implies potentially more than 2 rows in the table:
CREATE TABLE new LIKE ToDo;
INSERT INTO new
SELECT DISTINCT id, caption, ...
FROM ToDo;
RENAME TABLE ToDo TO old,
new TO ToDo;
DROP TABLE old;
Well, what a good reason for an auto-incremented column! Well, you can add one:
alter table todo add ToDoId int auto_increment primary key;
This also sets the value.
Then you can do:
delete td
from todo td join
todo td1
on td.id = td1.id and td.caption = td1.caption and . . . and
td1.id < td.id;
This assumes that the columns are not NULL.
Alternatively, fix the entire table:
create temporary table temp_todo as
select *
from todo;
truncate table todo;
insert into todo
select distinct *
from todo;
This handles NULL values better than the first version.
Along the way, fix the table to have an auto-incremented primary key, so you can avoid this problem forevermore.
I think I found it myself, I just got stuck for a sec!
DELETE FROM ToDo WHERE ... LIMIT 1;
Hello,
first of all I want you to show my table I have:
CREATE TABLE `channels` (
`channel_id` int(11) NOT NULL AUTO_INCREMENT,
`channel_name` varchar(45) DEFAULT NULL,
PRIMARY KEY (`channel_id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8
CREATE TABLE `gamepoints` (
`gp_id` int(11) NOT NULL AUTO_INCREMENT,
`gamble` int(11) DEFAULT NULL,
`roulette` int(11) DEFAULT NULL,
`blackjack` int(11) DEFAULT NULL,
`slots` int(11) DEFAULT NULL,
PRIMARY KEY (`gp_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
CREATE TABLE `player_channel` (
`pc_id` int(11) NOT NULL AUTO_INCREMENT,
`players_id` int(11) DEFAULT NULL,
`channel_id` int(11) DEFAULT NULL,
PRIMARY KEY (`pc_id`),
KEY `players_id_idx` (`players_id`),
KEY `channel_id_idx` (`channel_id`),
CONSTRAINT `channel_id` FOREIGN KEY (`channel_id`) REFERENCES `channels` (`channel_id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
CONSTRAINT `players_id` FOREIGN KEY (`players_id`) REFERENCES `players` (`players_id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8
CREATE TABLE `players` (
`players_id` int(11) NOT NULL AUTO_INCREMENT,
`p_name` varchar(45) DEFAULT NULL,
`p_right` varchar(45) DEFAULT NULL,
`gp_id` int(11) DEFAULT NULL,
PRIMARY KEY (`players_id`),
KEY `gp_id_idx` (`gp_id`),
CONSTRAINT `gp_id` FOREIGN KEY (`gp_id`) REFERENCES `gamepoints` (`gp_id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
I wanted to this query:
UPDATE gamepoints SET gamble = 1
WHERE gamepoints.gp_id = players.gp_id
AND players.p_name = "test"
AND player_channel.players_id = players.players_id
AND player_channel.channel_id = channels.channel_id
AND channels.channel_name = "test";
But when I do this i get this Error:
Error Code: 1054. Unknown column 'players.p_name' in 'where clause'
I don't know what I am doing wrong, i tryed also after set to add from with all tables, but this works also not.
I would be really happy if someone can help me :)
Thanks in advance
You omitted the table names of all but gamepoints. I would recommend that you use explicit join update syntax, which makes it harder to have this sort of error:
UPDATE gamepoints t1
INNER JOIN players t2
ON t1.gp_id = t2.gp_id
INNER JOIN player_channel t3
ON t3.players_id = t2.players_id
INNER JOIN channels t4
ON t4.channel_id = t3.channel_id
SET t1.gamble = 1
WHERE t2.p_name = 'test' AND
t4.channel_name = 'test';
If you wanted to salvage your current query, then it would start off looking something like this:
UPDATE gamepoints, players, player_channel, channels
SET gamble = 1
WHERE -- a very large number of conditions
One reason implicit joins are frowned upon is that they mix normal restrictions on the result set with join conditions, all in the same WHERE clause. This doesn't happen with the query as I wrote it using explicit joins.
I have this comments table with over 4 million rows:
CREATE TABLE `comments`
(
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`gid` int(11) unsigned NOT NULL DEFAULT '0',
`userid` int(6) unsigned DEFAULT NULL,
`date` int(11) unsigned DEFAULT NULL,
`comment` text NOT NULL,
`status` enum('on','alert') NOT NULL DEFAULT 'on',
PRIMARY KEY (`id`),
KEY `gid_2` (`gid`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
now I'm thinking about extracting the text-field to decrease the 400 MB and increase performance. Like this:
CREATE TABLE commentstext
(
id int(11) unsigned NOT NULL AUTO_INCREMENT,
`comment` text NOT NULL,
PRIMARY KEY (id)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
but I'm not sure if this will perform better this way. I need to test this cases by using different queries (also). My results so far differ a lot. Between 0.001* - 3.321 sec. I'm not able to check this by querying in phpmyadmin.
Is there a better and easy way or tool to compare queries performance?
That's what I was looking for:
SELECT BENCHMARK(1000000000, (
SELECT
comments.comment
FROM
comments
WHERE
`gid`=303410
LIMIT 1
));
(result 34.1612 sec.)
(result 32.2737 sec.)
SELECT BENCHMARK(1000000000, (
SELECT
commentstext.comment
FROM
commentsindex,
commentstext
WHERE
`gid`=303410
AND commentsindex.`id` = commentstext.`id`
LIMIT 1
));
(result 34.1237 sec.)
(result 34.2914 sec.)
SELECT BENCHMARK(1000000000, (
SELECT
commentstext.comment
FROM
commentsindex
INNER JOIN
commentstext
ON commentstext.`id` = commentsindex.`id`
WHERE
`gid`=303410
LIMIT 1
));
(result 32.8471 sec.)
(result 34.7079 sec.)
... but now I'm really wondering that it doesn't matter, which table design is in use. confused
I'm retrieving images stored as blobs in the database using a python script running on the same server.
SELECT *
FROM imagedb_production.imagedb IMAGE
LEFT JOIN dccms_production.tblmedia MEDIA ON IMAGE.name = MEDIA.name
LEFT JOIN dccms_production.tblmultimedia CAP ON MEDIA.contentItemID = CAP.contentItemID
LIMIT 5000,100;
An EXPLAIN returns
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE IMAGE index NULL name_idx 767 NULL 10145962 Using index
1 SIMPLE MEDIA ref name name 63 imagedb_production.IMAGE.name 1
1 SIMPLE CAP eq_ref PRIMARY,idx_contentItemID PRIMARY 4 dccms_production.MEDIA.contentItemID 1 Using index
(Sorry the output looks like crap)
This query takes close to 12 minutes is there any way I can speed this up before going through and tuning the mysql db instance?
Additional information
'imagedb', 'CREATE TABLE `imagedb` (
`multimediaID` int(11) NOT NULL auto_increment,
`name` varchar(255) NOT NULL,
`content` mediumblob,
`description` longtext,
`mime_type` varchar(255) default NULL,
PRIMARY KEY (`multimediaID`),
KEY `name_idx` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=2320759 DEFAULT CHARSET=utf8'
'tblmedia', 'CREATE TABLE `tblmedia` (
`mediaID` int(11) NOT NULL auto_increment,
`contentItemID` int(11) NOT NULL default ''0'',
`name` varchar(255) default NULL,
`width` int(11) default NULL,
`height` int(11) default NULL,
`file1Size` bigint(20) default NULL,
`file2Size` bigint(20) default NULL,
`mediaSlug` int(11) default NULL,
PRIMARY KEY (`mediaID`),
KEY `idx_contentItemID` (`contentItemID`),
KEY `name` (`name`(20))
) ENGINE=InnoDB AUTO_INCREMENT=899975 DEFAULT CHARSET=utf8'
'tblmultimedia', 'CREATE TABLE `tblmultimedia` (
`contentItemID` int(11) NOT NULL default ''0'',
`caption` text,
`mimeType` varchar(255) default NULL,
PRIMARY KEY (`contentItemID`),
KEY `idx_contentItemID` (`contentItemID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8'
You have 10,000,000 rows with no sorting, I would fix that. Add a default order by clause.
Older versions of MySQL did not take limit clauses into account until much later. I think newer versions do a better job of that. You might want to check into different ways to limit the result set.