All Questions

1126
votes
7answers
2.4m views

How do I list all databases and tables using psql?

I am trying to learn PostgreSQL administration and have started learning how to use the psql command line tool. When I log in with psql --username=postgres, how do I list all databases and tables? I ...
445
votes
2answers
229k views

What's the difference between a temp table and table variable in SQL Server?

This seems to be an area with quite a few myths and conflicting views. So what is the difference between a table variable and a local temporary table in SQL Server?
379
votes
4answers
706k views

How do you mysqldump specific table(s)?

How can I dump a specific table or set of tables without including the rest of the db tables?
278
votes
15answers
143k views

Can MySQL reasonably perform queries on billions of rows?

I am planning on storing scans from a mass spectrometer in a MySQL database and would like to know whether storing and analyzing this amount of data is remotely feasible. I know performance varies ...
257
votes
4answers
264k views

Why Does the Transaction Log Keep Growing or Run Out of Space?

This one seems to be a common question in most forums and all over the web, it is asked here in many formats that typically sound like this: In SQL Server - What are some reasons the ...
252
votes
4answers
457k views

How do I list all columns for a specified table

I'm looking for a precise piece of information in a database which I have no knowledge about. It's a 3rd party product, they are slow on answering some questions, and I know the data is lying inside ...
235
votes
10answers
230k views

What are the main differences between InnoDB and MyISAM?

What are the main differences between InnoDB and MyISAM?
223
votes
3answers
122k views

How can I time SQL-queries using psql?

I would like to benchmark some SQL-queries agains my PostgreSQL database. Is there any way I can time SQL-queries using psql?
221
votes
17answers
103k views

How do you document your databases?

I find that most of my clients are not documenting their databases at all and I find that pretty scary. To introduce some better practice, I would like to know what tools/process people are using. ...
218
votes
4answers
419k views

How do I list all schemas in PostgreSQL?

When using PostgreSQL v9.1, how do I list all of the schemas using SQL? I was expecting something along the lines of: SELECT something FROM pg_blah;
190
votes
11answers
152k views

How can I monitor the progress of an import of a large .sql file?

I am importing a 7 GB foobar.sql to restore a table in a local database. $ mysql -h localhost -u root 'my_data' < foobar.sql $ mysql --version /usr/local/mysql/bin/mysql Ver 14.12 Distrib 5.0....
181
votes
6answers
66k views

When should I use a unique constraint instead of a unique index?

When I want a column to have distinct values, I can either use a constraint create table t1( id int primary key, code varchar(10) unique NULL ); go or I can use a unique index create table t2( id ...
169
votes
11answers
387k views

connect to PostgreSQL server: FATAL: no pg_hba.conf entry for host

Hello I am trying to run a website sent to me but after doing so this error appeared connect to PostgreSQL server: FATAL: no pg_hba.conf entry for host "4X.XXX.XX.XXX", user "userXXX", database "...
167
votes
7answers
194k 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 ...
165
votes
7answers
162k views

What's the difference between a CTE and a Temp Table?

What is the difference between a Common Table Expression (CTE) and a temp table? And when should I use one over the other? CTE WITH cte (Column1, Column2, Column3) AS ( SELECT Column1, Column2, ...
163
votes
3answers
367k views

How to insert values into a table from a select query in PostgreSQL?

I have a table items (item_id serial, name varchar(10), item_group int) and a table items_ver (id serial, item_id int, name varchar(10), item_group int). Now I want to insert a row into items_ver ...
160
votes
5answers
111k views

When should a primary key be declared non-clustered?

While creating a test database for another question I asked earlier, I remembered about a Primary Key being able to be declared NONCLUSTERED When would you use a NONCLUSTERED primary key as opposed ...
157
votes
4answers
258k views

How large should be mysql innodb_buffer_pool_size?

I have a busy database with solely InnoDB tables which is about 5GB in size. The database runs on a Debian server using SSD disks and I've set max connections = 800 which sometimes saturate and grind ...
156
votes
19answers
45k views

Should developers be able to query production databases?

Should developers be given permission to query (SELECT / read only) production databases? The previous place I worked, the development team had the db_datareader role; where I work now the ...
144
votes
5answers
362k views

Granting access to all tables for a user

I'm new to Postgres and trying to migrate our MySQL databases over. In MySQL I can grant SELECT, UPDATE, INSERT, and DELETE privileges on a low privileged user and enable those grants to apply to all ...
143
votes
3answers
115k views

Help installing SQL Server 2017 - VS Shell installation has failed with exit code 1638

Any suggestions on how to deal with this error: TITLE: Microsoft SQL Server 2017 Setup ------------------------------ The following error has occurred: VS Shell installation has failed with exit ...
129
votes
13answers
237k 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, ...
123
votes
6answers
308k views

List the database privileges using psql

I'm in the middle of a database server migration and I can't figure (after googling and searching here) how can I list the database privileges (or all the privileges across the server) on PostgreSQL ...
123
votes
2answers
230k views

Create a MySQL database with charset UTF-8

I'm new to MySQL and I would like to know: How can I create a database with charset utf-8 like I did in navicat? create mydatabase; ...seems to be using some kind of default charset.
120
votes
2answers
117k views

Granting a user account permission to create databases in PostgreSQL

How do I give a user account in PostgreSQL the ability to create and drop databases? Is there a way to do this with GRANT?
119
votes
8answers
45k views

Why shouldn't we allow NULLs?

I remember reading this one article about database design and I also remember it said you should have field properties of NOT NULL. I don't remember why this was the case though. All I can seem to ...
118
votes
5answers
178k views

Possible to make MySQL use more than one core?

I've been presented with some dedicated MySQL servers that never use more than a single core. I'm more developer than DBA for MySQL so need some help Setup The servers are quite hefty with an OLAP/...
114
votes
12answers
51k views

Should binary files be stored in the database?

What is the best place for storing binary files that are related to data in your database? Should you: Store in the database with a blob Store on the filesystem with a link in the database Store in ...
112
votes
12answers
135k views

How do I find PostgreSQL's data directory?

I forgot how I last time started postgres (it was months ago) and I don't remember where the data directory is located at. The postgres command seems to require to location. I'm on MacOsX if that ...
108
votes
4answers
16k views

Why are numbers tables “invaluable”?

Our resident database expert is telling us that numbers tables are invaluable. I don't quite understand why. Here's a numbers table: USE Model GO CREATE TABLE Numbers ( Number INT NOT NULL, ...
104
votes
6answers
109k views

How to determine if an Index is required or necessary

I've been running an auto-index tool on our MS SQL database (I modified a script originating from Microsoft that looks at the index statistics tables - Automated Auto Indexing). From the stats, I now ...
104
votes
5answers
163k views

How to safely change MySQL innodb variable 'innodb_log_file_size'?

So I'm fairly new to tuning InnoDB. I'm slowly changing tables (where necessary) from MyIsam to InnoDB. I've got about 100MB in innodb, so I increased the innodb_buffer_pool_size variable to 128MB: ...
103
votes
3answers
58k views

Advantages and Disadvantages to using ENUM vs Integer types?

Lets say in some random table, you have a column named status. It's real-world values would be either enabled or disabled. Is it better for this column's data type to be an int/bool (1 or zero) or to ...
100
votes
8answers
36k views

Where are some useful SQL puzzles to teach SQL in a workplace?

I'm looking for beginner and intermediate level SQL puzzles, that I can point trainees at for practice. I'm aware of http://sqlzoo.net/ which is a great resource - is there anything else out there ...
99
votes
3answers
357k views

ALTER TABLE - Rename a column

This is driving me nuts! I want to rename a column from read-more to read_more in my blog table I tried all this: ALTER TABLE blog RENAME COLUMN read-more to read_more; ALTER TABLE blog CHANGE ...
99
votes
11answers
83k views

SQL: SELECT All columns except some

Is there a way to SELECT all columns in a table, except specific ones? IT would be very convenient for selecting all the non-blob or non-geometric columns from a table. Something like: SELECT * -...
97
votes
4answers
32k views

Why use both TRUNCATE and DROP?

In the system I work on there are a lot of stored procedures and SQL scripts that make use of temporary tables. After using these tables it's good practice to drop them. Many of my colleagues (almost ...
97
votes
4answers
160k views

Good explanation of cascade (ON DELETE/UPDATE) behavior

I don't design schemas everyday, but when I do, I try to setup cascade updates/deletes correctly to make administration easier. I understand how cascades work, but I can never remember which table is ...
97
votes
4answers
127k views

Force drop db while others may be connected

I need to remove a database from a PostgreSQL DB cluster. How can I do it even if there are active connections? I need sort of a -force flag, that will drop all connections and then the DB. How can I ...
96
votes
8answers
16k views

Does SQL Server read all of a COALESCE function even if the first argument is not NULL?

I'm using a T-SQL COALESCE function where the first argument will not be null on about 95% of the times it is ran. If the first argument is NULL, the second argument is quite a lengthy process: ...
96
votes
5answers
24k 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 ...
95
votes
7answers
261k views

How do I move SQL Server database files?

I have a database and want to move the .mdf and .ldf files to another location. But I do not want to stop the MSSQLSERVER service, and I do not want to export to another server. How can I do this?
92
votes
15answers
63k views

Why is Database Administration so hard?

I know a lot of Database Administrators and they are all over 28-29 years old. Is all database administration like that? I mean, is this about getting experience more than at least 7-8 years? Or is ...
89
votes
19answers
25k views

Is adding the ‘tbl’ prefix to table names really a problem?

I’m watching some Brent Ozar videos (like this one, for instance) and he suggests not prefixing tables with ‘tbl’ or ‘TBL’. On the internet I found some blogs saying it adds nothing to documentation,...
89
votes
5answers
53k views

When to use TINYINT over INT?

In general, I always use Ints. I know that in theory this is not the best practice, though, since you should use the smallest data type that will be guaranteed to store the data. For example, it's ...
89
votes
7answers
59k views

Guid vs INT - Which is better as a primary key?

I've being reading around reasons to use or not Guid and int. int is smaller, faster, easy to remember, keeps a chronological sequence. And as for Guid, the only advantage I found is that it is ...
87
votes
5answers
20k views

Why can't RDBM's cluster the way NoSQL does?

One of the big plusses for nosql DBMS is that they can cluster more easily. Supposedly with NoSQL you can create hundreds of cheap machines that store different pieces of data and query it all at ...
87
votes
6answers
46k views

Retrieving n rows per group

I often need to select a number of rows from each group in a result set. For example, I might want to list the 'n' highest or lowest recent order values per customer. In more complex cases, the ...
87
votes
4answers
82k views

Optimizing queries on a range of timestamps (two columns)

I use PostgreSQL 9.1 on Ubuntu 12.04. I need to select records inside a range of time: my table time_limits has two timestamp fields and one integer property. There are additional columns in my ...
87
votes
3answers
86k views

PostgreSQL multi-column unique constraint and NULL values

I have a table like the following: create table my_table ( id int8 not null, id_A int8 not null, id_B int8 not null, id_C int8 null, constraint pk_my_table primary key (id), ...

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