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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10
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2answers
19k views

Should I increase max_connections in AWS RDS t1-micro for MySQL?

I have an AWS RDS t1-micro running MySQL 5.5. It gives me too many connections error. I checked and it allows 34 maximum connections concurrently. What I have read is that i can increase this max ...
10
votes
2answers
20k views

Why is MySQL is creating so many temporary tables on disk?

Can any configuration mistake lead to creating too many temp tables by mysql..mysql tuner shows Current max_heap_table_size = 200 M Current tmp_table_size = 200 M Of 17158 temp tables, 30% were ...
10
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3answers
3k views

Problem with MySQL subquery

Why does this query DELETE FROM test WHERE id = ( SELECT id FROM (SELECT * FROM test) temp ORDER BY RAND() LIMIT 1 ); sometimes delete 1 row, ...
10
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3answers
4k 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 ...
10
votes
2answers
27k views

How to cast an integer to a boolean in a MySQL SELECT clause?

I'm new here so be kind to me. I have the following scenario: I have many tables which, for the sake of simplicity, are represented in a View in my MySQL database. My problem is that I need a value ...
10
votes
4answers
12k 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 ...
10
votes
1answer
11k 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: ...
10
votes
1answer
130 views

Server responds with empty packet during session negotiation resulting in client giving a malformed packet error

I'm attempting to connect to a remote mysql server. This happens 100% of the time. client: mysql Ver 14.14 Distrib 5.7.12, for Win32 (AMD64) server: 5.0.95 This is the error I get: C:\>mysql -h ...
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votes
3answers
2k views

Is a 5+ column primary key bad for large (100 million+) table?

I was reading about some real life DB issues, and one project had a 100 million row plus table that had 5 columns as its primary. I'm thinking this is bad, but can anyone tell me exactly why? The ...
10
votes
2answers
6k views

PostgreSQL vs. MySQL - Advantages / Disadvantages with a spatial component

We are the in the process of building out a web application that has a spatial data component. In the beginning our spatial data comparisons will take a given point and return matched overlapping ...
10
votes
1answer
8k views

Is it possible to change ENUM() lists?

I wasn't sure if changing ENUM() list isn't possible so I made a test. In MySQL v5.1.58 I made a test InnoDB table that contains one field called 'bool' of type ENUM('yes', 'no'). Then I executed... ...
10
votes
2answers
19k views

What is the reason of Host 'host_name' is blocked in MySQL?

When I use incorrect password to connect to mysql server, and the test count is over the max_connect_errors, and I find the Aborted_connects is also arise as the count I test, but the host is still ...
10
votes
1answer
13k views

Struggling to debug high CPU usage on Amazon RDS MySQL instance

We're running an m1.xlarge MySQL RDS server and having some issues with high CPU usage. We had some problems a couple of weeks ago with CPU utilization reaching 100% on a large instance. When we ...
10
votes
2answers
262 views

Find total duration of each consecutive series of rows

MySQL Version The code will run in MySQL 5.5 Background I have a table like the following one CREATE TABLE t ( id INT NOT NULL AUTO_INCREMENT , patient_id INT NOT NULL , bed_id INT NOT NULL , ...
10
votes
2answers
60k views

How to speed up queries on a large 220 million rows table (9 gig data)?

The issue: We have a social site where members can rate each other for compatibility or matching. This user_match_ratings table contains over 220 million rows (9 gig data or almost 20 gig in ...
10
votes
4answers
9k views

Adding an index very slow…is there a mysql cmd to get an ETA or show progress?

I'm currently running an alter query on my table (20M entries) in order to add an index. it's running for more than 3 days already (stuck on 'copy to tmp table'). is there a way I can see the ...
10
votes
1answer
878 views

Calculate MATCH() AGAINST() scores from UNIFIED QUERY not FOR EACH TABLE

I am trying to have a score for entire section of SELECT statements SELECT *,MATCH(`result`) AGAINST('keyword') as `score` FROM `table1` WHERE MATCH(`result`) AGAINST('keyword') UNION SELECT ...
10
votes
1answer
738 views

Disable explicit commits in JDBC, detect them in SQL, or put the database in a readonly state

Background: I'm working on http://sqlfiddle.com (my site), and am trying to prevent one avenue of abuse possible there. I'm hoping that by asking about a problem I'm currently addressing, I don't ...
10
votes
1answer
139 views

How to estimate the I/O operations performed by MySQL queries?

On Amazon's RDS, you pay about $0.10 per 1 million I/O requests. I've noticed a very high number (in hundreds of thousands) of I/O requests for a very low traffic database. On seeing this, I did some ...
9
votes
4answers
7k views

How costly is opening and closing of a DB connection?

How CPU intensive is opening and closing of a DB connection (for a web app) in MySQL ... when the DB software is on localhost? ... when the DB software is on another machine?
9
votes
1answer
21k views

Performance difference between MySQL and PostgreSQL for the same schema/queries [closed]

I'm a newbie DBA, and I have experience in Microsoft SQL Server but I want to jump to FLOSS. I'm starting a company, and we develop an app (PHP) with a Postgres backend, and we did some tests ...
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votes
3answers
21k views

MySQL Error Reading Communication Packets

In MySQL error logs, I see these quite few a warnings like these: 120611 16:12:30 [Warning] Aborted connection 2619503 to db: 'db_name' user: 'user_name' host: 'webapp_hostname' (Got an error reading ...
9
votes
3answers
315 views

How to avoid a cyclic dependency (circular reference) between 3 tables?

I have 3 tables: People Post Likes When I design the ER model it has a cyclic dependency: 1:N People --------< Post 1:N Post ----------< Likes 1:N People ...
9
votes
3answers
62k views

select rows where column contains same data in more than one record

I have a table that has a column called article_title. Let's say the table name is articles. I need to find out the records where the article_title data is the same on more than one record. Here's ...
9
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3answers
6k views

How to stress test a SQL server?

I've been tasked to stress test our MSSQL Server and MySQL Server. I would like to know if there are any tools or scripts which I could use on our current systems and the new system to compare ...
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votes
4answers
19k views

Any option for mysqldump to ignore databases for backup?

We have 40 databases in our server. We want to take 36 databases backup using mysqldump. How can i ignore remaining 4 databases in mysqldump command? Is there any option for mysqldump to ignore ...
9
votes
3answers
19k views

How to Log All mysql queries into log file?

I am using Mysql 5.6.12 under Wamp server environment. Now I want to log All queries into ".log" file, the queries which are running by PHP or from PHPMyAdmin, I want to log them...
9
votes
6answers
10k views

How to search a MySQL database with encrypted fields

Suppose I need to encrypt certain table-fields of a MySQL database. Additionally, I need to search some of those fields I did encrypt. How would one search those fields anyway? Decrypting each ...
9
votes
2answers
131k views

How to resolve too many connections and fatal error in mysql running on vps

I am running an application PHPlist on my linode server, simultaneously running 12 PHP scripts, each of which opens a MySQL connection. Now when I access PHPlist it often shows this error: Fatal ...
9
votes
2answers
11k views

MySQL equivalent of WITH in oracle

Is there a MySQL equivalent of the WITH clause in Oracle?
9
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2answers
8k views

Running SQL Query on all databases

I have one hosting account using cPanel and phpmyadmin. I have 50 databases under this account, all WordPress. I need this query modified so that it runs through all databases to update the ...
9
votes
3answers
16k views

How can I determine how many IOPs I need for my AWS RDS database?

I am migrating part of a mysql database into AWS. The data in question is 99% write, and each row has about 1k of varchar fields, a datetime and 4 ints. I estimate that we will need between 20-25k ...
9
votes
1answer
9k views

Why would an UPDATE SET REPLACE() statement match rows, but change none and give no warnings?

I'm seeking a certain string in a field and want to replace it with a new string. Specifically, I want all references to one URL to be changed to another URL. I've crafted this SQL statement and am ...
9
votes
4answers
2k views

How can I optimize this MySQL query further?

I have a query that is taking a particularly long time to run (15+ seconds) and it is only getting worse with time as my dataset grows. I have optimized this in the past, and have added indices, ...
9
votes
2answers
10k views

Why does MySQL allow HAVING to use SELECT aliases?

In SQL, as far as I know, the logical query processing order, which is the conceptual interpretation order, starts with FROM in the following way: FROM WHERE GROUP BY HAVING SELECT ORDER BY ...
9
votes
3answers
15k views

How do you re-sync the Master MySQL DB with Slave DB changes if the Master goes offline?

MySQL Server 1 is running as Master. MySQL Server 2 is running as Slave. With both DBs online, they are in "perfect sync". If Slave goes offline, there's no problem if Master still online; they will ...
9
votes
1answer
5k views

How can I determine the size of a dump file prior to dumping?

How can I determine or estimate the size of the SQL dump file prior to using something like mysqldump?
9
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2answers
10k views

mysql.proc keeps crashing, cannot do a mysqldump?

Due to some problems with InnoDB, I'm going to dump all databases to a new server: mysqldump -E -R --all-databases | pv -b | mysql -u root -p -h new.server The dump process stopped with ...
9
votes
3answers
3k views

MySQL High Performance for Lots of SELECTs/INSERTs/UPDATEs/DELETEs

I am creating a module where every user often gets a record into a table for 10 to 300 seconds. When the time expires a record gets deleted. The case is: there will be a lot of users and records will ...
9
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2answers
4k views

Will these two queries result in a deadlock if executed in sequence?

This is almost certainly the cause of my other question, but I thought it was worth separating the two as I have a hypothesis based on the following log that I would love to have falsified or ...
9
votes
1answer
264 views

Power went out - Did query finish?

Is there a way to check and see if a query finished? I ran 3 very long running update queries (+/- 25 hours each) as I went out the door for vacation last week. Unfortunately, somewhere during the ...
9
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3answers
14k views

Cache MySQL database in memory

I am having problems with a website with 600MB of MySQL database. The website is way too slow. I noticed the bigger the MySQL database gets, the slower it goes. When it was 5MB, the website was very ...
9
votes
2answers
1k views

Do I need to add a new single column index to a table if a multi-column index on that field already exists?

I've a table with a multi-column UNIQUE index on _job_id__ and __keyword_id__. Would I also need to add another index to __job_id__ if I have a frequent query which performs a GROUP BY on that ...
9
votes
3answers
22k views

What is the benefit of using BOOLEAN over TINYINT(1)?

From MySQL manual, it says: BOOL, BOOLEAN These types are synonyms for TINYINT(1). A value of zero is considered false. Nonzero values are considered true: I created a BOOLEAN column with ...
9
votes
4answers
18k views

How to get the most out of MySQL on a QuadCore machine with 16 GB of RAM?

I'm running a MySQL 5.5 server on my workstation for scientific data analysis and wonder how to configure MySQL in order to get the most out of it performance-wise. The types of query that I typically ...
9
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3answers
16k views

How to use insert delay with the InnoDB engine and use less connection for insert statements?

I'm working on an application which involves a lot of database writes, approximately ~70% inserts and 30% reads. This ratio would also include updates which I consider to be one read and one write. ...
9
votes
1answer
7k views

Is there such thing as Custom Data Types?

Does MySQL have any support for custom data types? For example, zip codes might be stored in a varchar(10) field, but they could be compacted in to an int, with options for blank, and a flag as to ...
9
votes
1answer
11k views

Autoincrement primary key in CREATE TABLE … AS SELECT

I created table using a complicated select query via CREATE TABLE ... AS SELECT.... How can I add an autoincrement primary key in this query? For example: create table `user_mv` select ...
9
votes
2answers
7k views

Monitor MySQL activity per database?

What is the best way to monitor activity on each database of my server ? I tried mtop/mytop which display activity in real time but aren't very practical to see all the queries executed on it. I ...
9
votes
2answers
5k views

Trouble deciphering a deadlock in an innodb status log

We are accessing MySQL from the Microsoft ADO.NET connector. Occasionally we are seeing the following deadlock in our innodb status and haven't been able to identify the cause of the problem. It ...