Questions tagged [mysql]

All versions of MySQL (not Microsoft SQL Server). Please also add a version-specific tag like mysql-5.7 if that is relevant to the question.

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4
votes
7answers
10k views

What database front end do you use? [closed]

What database front end do you use? It should let you manage databases, tables, indexes and ideally even data records. And it should ideally be free so we can all use it too. Databases that it could ...
6
votes
4answers
7k views

Why does this Entity Framework query perform so bad in MySQL?

Let me give you a little setup. We have a InnoDB table on MySQL 5.1 with close to 20 million records, no foreign keys, and proper indexes for queries we do. We are using the latest 6.3.5 MySQL ...
4
votes
3answers
12k views

Confirm that my.cnf file has loaded OK

Does anyone know if there is a way to confirm if any my.cnf file is being read by MySQL? I only have the one my.cnf on the machine (and there are no my.ini files) which I have in /etc/my.cnf. When I ...
10
votes
4answers
26k views

Replicating a remote MySQL database to MS SQL Server 2008

I want to replicate the contents of a MySQL database to a MS SQL Server 2008 database. Is this possible? Can anyone outline the steps required in order to achieve this? Thanks.
8
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2answers
5k views

How do I search to see if a MySQL user exists on the system?

I'm not finding a user by show grants for 'username'@'localhost'' I'm thinking that perhaps the username is slightly different, so I want to do a wildcard search of all the database users. How can I ...
11
votes
4answers
24k views

Audit logins on MySQL database

Is there a way to audit logins to MySQL? I'd like to be able to create a username for each employee and thereby create an audit trail of logins. However, googling has turned up no good results. The ...
3
votes
3answers
523 views

What kind of hardware/software config should I look at for a MySQL database with 10,000 plus tables

I am looking at rolling out a CMS system that will require the creation of around 10,000 tables within the primary MySQL database of the system. The database will be the data store for several ...
0
votes
1answer
667 views

One record, multiple updates in one query (MySQL)

I run into a problem for which I didn't find an answer anywhere: If I have a table in which one specific value(here amount) from multiple records can add into a target record(from the same table), can ...
9
votes
2answers
7k views

How can you stop MySQL slave from replicating changes to the 'mysql' database?

I have my slave set to not replicate the 'mysql' database as described in this SHOW SLAVE STATUS\G; Slave_IO_State: Waiting for master to send event Master_Host: 127.0.0.1 ...
20
votes
4answers
828 views

Is "CREATE INDEX` in MySQL a Linear Operation?

What I mean is the following: If creating an index on a table with n rows takes t time. Will creating an index on the same table with 1000*ntake approximately 1000*t time. What I'm trying to achieve ...
18
votes
4answers
37k views

How do I find out if a procedure or function exists in a mysql database?

How do I find out if a procedure or function exists in a mysql database? and is there any discovery option? like a show procedures; (e.g. like show tables;)
21
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2answers
8k views

Can I create index on a table in a MySQL database while in use

And if I can, any reason (performance/stability) why I shouldn't?
2
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2answers
515 views

Transferring concepts - users/groups/permissions of db objects from mysql to postgresql

This seemed like a better fit here than stackoverflow, so here goes: I've been using mysql for a while since on most of the cheap webhosts it is the provided database. However, now I've started ...
13
votes
5answers
4k views

Is it unwise to run replication on same physical server?

I'm contemplating setting up a Master-Slave replication for my database. The slave server will be used for redundancy and possibly a reports server. However, one of the biggest issues I'm running into ...
5
votes
1answer
365 views

MySQL and Solid State Disks on EMC

Since all writes and sequential reads are cached by the EMC storage system, the best use for solid state disk is to store data that has a random READ pattern. On Oracle, that is the temp tablespace ...
7
votes
4answers
2k views

Can you “su -” in MySQL?

If I have root on a mysql database and I want to drop privileges to that of a normal user, without using their password, can I do it? if so how? think # su - username on unix. Basically, I'm just ...
3
votes
1answer
647 views

MySQL CREATE statement are really slow (Mac OS X / Macport install) [closed]

I recently noticed that recreating the database for the web application I am working on is taking a lot of time. I had just reinstalled Mysql from Macport... I am getting really lousy performances, ...
5
votes
1answer
1k views

Foreign Key violation - not sure why

I have the following two tables with a foreign key on status_id: mysql> describe usr_cookbook; +-----------+-----------+------+-----+-------------------+-------+ | Field | Type | Null | ...
25
votes
8answers
22k views

Tool to generate large datasets of test data [closed]

Many times when trying to come up with an efficient database design the best course of action is to build two sample databases, fill them with data, and run some queries against them to see which one ...
18
votes
4answers
2k views

How do convert a 66,862,521 row table from MyISAM to InnoDB without going offline for several hours?

is it possible (and how) to convert a huge MyISAM table into InnoDB without taking the application offline. It requires to insert a couple of rows into that table every second but it is possible to ...
9
votes
1answer
13k views

Error creating foreign key from MySQL Workbench

I'm trying to synchronize schema changes from MySQL Workbench to my database. I'm getting the following error when it tries to create a foreign key: Executing SQL script in server ERROR: Error 1005: ...
45
votes
6answers
25k views

Performance implications of MySQL VARCHAR sizes

Is there a performance difference in MySQL between varchar sizes? For example, varchar(25) and varchar(64000). If not, is there a reason not to declare all varchars with the max size just to ensure ...
19
votes
2answers
37k views

What is the difference between MySQL VARCHAR and TEXT data types?

After version 5.0.3 (which allowed VARCHAR to be 65,535 bytes and stopped truncating trailing spaces), is there any major difference between these two data types? I was reading the list of ...
21
votes
3answers
16k views

Is it common practice to mix InnoDB and MyISAM tables on same server?

I've got a single database of about 4.5GB running on a server with 8GB RAM. The vast majority of the tables are MyIsam (about 4.3GB), but I'm soon going to be converting some of them to InnoDB. (It's ...
30
votes
1answer
51k views

INT(5) vs SMALLINT(5): numbers in parenthesis after the numeric type

In MySQL table definitions is there a different between INT(5) and SMALLINT(5)? Or do they both represent the same size?
13
votes
3answers
6k views

Dynamic SQL in MySQL stored routines

According to the restrictions on stored routines and triggers, dynamic sql cannot be used (restriction lifted for stored procedures in version 5.0.13 and later). Why is this limitation in place? And ...
7
votes
1answer
2k views

What are some important MySQL status variables to keep an eye on? [closed]

I'm a fairly new DBA with a programming background. As such, I like to build tools to manage tasks to help me familiarize myself with the intricacies of a technology. In this case, I am managing ...
6
votes
2answers
471 views

different login credentials based on user

I run a PHP symfony-framework web app for my company and it uses a single database login for all connections, whether the user is an admin or a client. I know that higher security systems often use ...
1
vote
1answer
157 views

version controll application/system for mysql databases [duplicate]

Possible Duplicate: Keeping track of schema changes Hello, How do you keep your mysql database schema under version control.
8
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3answers
202 views

Is there a performance gain by handling data with stored procedures versus feeding it into functions after retrieval?

Title sums it up. I'm reasonably well off with PHP, and comfortable getting it to do what I need it to with values pulled from MySQL, however in the interest of expanding my knowledge I've been ...
99
votes
5answers
27k views

Storing vs calculating aggregate values

Are there any guidelines or rules of thumb to determine when to store aggregate values and when to calculate them on the fly? For example, suppose I have widgets which users can rate (see schema ...
31
votes
3answers
8k views

Character vs Integer primary keys

I'm designing a database with multiple lookup tables containing possible attributes of the main entities. I'm thinking of using a 4 or 5-character key to identify these lookup values rather than an ...
6
votes
4answers
2k views

Is there a way to measure replication lag in MySQL with a resolution less than 1 second?

Is there a way by which you can measure replication lag in MySQL with a resolution of less than 1 second? That is, can replication lag be measured on the microsecond or millisecond level?
5
votes
1answer
387 views

What are the pros and cons of using the Sphinx Storage Engine?

What are the pros/cons of using the Sphinx Storage Engine in MySQL (doc) over the normal api?
40
votes
5answers
67k views

How do you tune MySQL for a heavy InnoDB workload?

Assuming a production OLTP system with predominantly InnoDB tables What are the common symptoms of a mistuned/misconfigured system? What configuration parameters do you most commonly change from ...
4
votes
2answers
193 views

How to create multiple entries on index based on the fields of one row?

I never found a good way to index multiple fields of one row as entries of an index or simulate this feature on MySQL. The problem arises when you have fields working as tags or similar concept. Ex.: ...
140
votes
13answers
254k views

How can I move a database from one server to another?

How can I move MySQL tables from one physical server to another? Such as this exact scenario: I have a MySQL server that uses innodb table and is about 20GB size. I want to move it to a new server, ...
7
votes
4answers
5k views

For a MySQL query, how do you determine physical and logical I/O?

I'm used to having a showplan in Microsoft SQL and have gotten lazy with using tools to tune MySQL queries. How can I determine physical/logical I/O for a query in MySQL? (EXPLAIN shows the index ...
7
votes
1answer
2k views

What's the maximum number of tables that can be referenced in a query in MySQL?

In the days of SQL Server 2000 and 2005, the maximum number of tables in a query was 256. Does MySQL have a similar limitation? I know that such query of such size means that either there's ...
4
votes
1answer
377 views

Using CoreData on a client-side application

This may be a bit more of an SO question, but... If I'm writing a client-side application for OS X that's going to sync with an online MySQL database, is there any difference on if I have CD use ...
28
votes
3answers
43k views

How can I change the default storage engine in phpmyadmin?

I use InnoDB almost exclusively in my applications. However, if I'm not careful when setting up the table, I forget to change it and phpmyadmin sticks me with MyISAM. Is there a way to change the ...
18
votes
6answers
359 views

Securing DB passwords

Looking at the structure of most PHP/MySQL-based websites I've seen, it appears that it's not terribly difficult to discern the database password if you dig a bit, as there's invariably a setup or ...
8
votes
3answers
323 views

What does the output of a JOIN statement look like?

I've been wanting to use joins for a while, but I'm having trouble visualizing the output so I know how to put it to use. Let's say I have 2 tables: CREATE TABLE Cities ( id INT UNSIGNED PRIMARY ...
8
votes
3answers
2k views

MySQL LDAP authentication

Is LDAP authentication and authorization in MySQL possible? What are the requirements (MySQL version, third-party software etc.)? How it's organized? Thanks.
7
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6answers
1k views

Alternative Database Tools for Web Admin [closed]

I currently use phpmyadmin for most of my database administration. It works well enough, but I'm interested in other tools that might work more quickly/efficiently/etc... What are the best and/or ...
41
votes
2answers
18k views

NULL or NOT NULL by default?

In MySQL, is it better to always allow nulls unless you know a field is required, or always use Not Null unless you know a field will contain nulls? Or doesn't it matter? I know in some DBMSs they ...
24
votes
5answers
12k views

How to create a conditional index in MySQL?

How to create an index to filter a specific range or subset of the table in MySQL? AFAIK it's impossible to create directly but I think it's possible to simulate this feature. Example: I want to ...
12
votes
5answers
8k views

Are there any MySQL Benchmarking tools? [closed]

I've heard a long time ago that there is this tool that helps you tweek mysql settings for better performance but i can't seam to find it. I am aware that I can use ab for apache to simulate high ...
24
votes
5answers
52k views

Where can I find the mysql slow log?

Just as the title says, where can I see it ? Are there any config options for it ( like how many ms would determine if a query is slow or not ) ?
177
votes
7answers
214k views

How can I optimize a mysqldump of a large database?

I have a symfony application with an InnoDB database that is ~2GB with 57 tables. The majority of the size of the database resides in a single table (~1.2GB). I am currently using mysqldump to ...