I have worked with databases before where the key attributes for entities looked like
83NG92R8B202NG
I am trying to build a db myself and was wondering if there was a sql command that automatically assigned a key to an added tuple or I had to create some sort of random attribute algorithm myself.
Why not use a UUID? More information in mysql docs:
http://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#function_uuid
If that doesn't fit your needs, take a look at this topic:
Generating a random & unique 8 character string using MySQL
Related
I have a database of articles that I want to search through. I had been using normal Django ORM to search, which was getting way to slow and then I got to know a little about Indexes in Django. I'm using MySQL and I now know that with MYSQL I cannot put an index field into a TextField as described here in this stack question which I was facing. However in my case I can't change this to CharField.
I was reading through the MyQSL Docs which stated
MySQL cannot index LONGTEXT columns specified without a prefix length
on the key part, and prefix lengths are not permitted in functional
key parts.
Hence I was of the understanding that since TextField in Django is LONGTEXT for MYSQL, I came across this Django-MySQL package here and thought that using this if I could change the LONGTEXT to a MEDIUMTEXT using this package, this might get resolved. So my updated model I did this
class MyModel(Model):
........
document = SizedTextField(size_class=3)
However, I still see the same error while applying python manage.py makemigrations
django.db.utils.OperationalError: (1170, "BLOB/TEXT column 'document'
used in key specification without a key length")
How can I go about resolving this?
returning all the articles that contain a given word passed by the client. So would be something SELECT * from articles WHERE text CONTAINS searchword
Add
FULLTEXT(text)
and use
WHERE MATCH(text) AGAINST("searchword")
or perhaps
WHERE MATCH(text) AGAINST("+searchword" IN BOOLEAN MODE)
It will run very fast. There are caveats -- short words and "stop" words (like "the") are ignored.
(If DJango cannot facilitate that, then you have to do it with "raw SQL".)
All of these related types, TEXT, MEDIUMTEXT, and LONGTEXT, are too large to be indexed without specifying a prefix. An index prefix means that only the first N characters of the string are included in the index. Like this:
create table mytable (
t text,
index myidx (t(200))
);
The prefix length in this example is 200 characters. So only the first 200 characters are included in the index. Usually this is enough to help performance, unless you had a large number of strings that are identical in their first 200 characters.
The longest prefix that MySQL supports depends on the storage engine and the row format. Old versions of MySQL support index prefix up to 768 bytes, which means a lesser number of characters depending on if you use multi-byte character sets like utf8 or utf8mb4. The recent versions of MySQL default to a more modern row format, which supports up to 3072 bytes for an index, again reduced by 3 or 4 bytes per character.
I'm not a regular Django user, so I tried to skim the documentation about defining indexes on model classes. But given a few seconds of reading, I don't see an option to declare a prefix for an index on a long string column.
I think your options are one of the following:
Change the column to a shorter string column that can be indexed
Create the index using the MySQL client, not using Django migrations
I've a web app developed by java. Currently I'm in a part of my app that I need to use MySql like in order to search for a string in mysql table contain 100000+ rows. When I had my research I found that MySql like doesn't use indexes but if you have the wildcard at the end of your string example: hello% but I need %hello% which like doesn't use index in these kinds of wildcards. And I also read on the internet that there are other technologies such as postgresql which can give you the ability of using indexes for searching string.
My question is Just because of like do I need to change MySql DB with all it's other features to postgresql DB, Do we have any alternative way on MySql To search for a string that uses indexes?, Do I Install them both and use each for it's own use ( If there is no other way );
All replies are much appreciated.
Do we have any alternative way on MySql To search for a string
Have you looked into MySQL Full-Text Search which uses fulltext index; provided you are using either InnoDB or MyISAM engine
I have a new client that is running a Symfony application with 170 or so MySQL tables. He recently updated his MySQL Workbench to the latest revision and is now getting a warning pop-up when he launched the application
FIX INDEX NAMES
Index names identical to FK names were found in the model, which is not allowed for MySQL5.5 and later. Would you like to rename the indexes?
I am not a DBA but I understand that the index and primary key names are clashing. What are the implications of renaming these indexes vs. just ignoring?
The Symfony app he is running uses the Doctrine ORM, would any queries or the model need to be updated should the indexes be renamed?
Using the InnoDB engine
Thanks
MySQL Workbench checks at opening a model if there are any duplicate index names and offers to rename them to be unique. Letting it doing this has not bad side effect. In fact it is even necessary to be able to apply the model to a server. Otherwise the server will refuse to create tables that contain an index with a name that was already taken.
So in short: it's a good idea to let Workbench fix this bug (since duplicate key names are nothing but a bug).
I have a dataset with a lot of columns I want to import into a MySQL database, so I want to be able to create tables without specifying the column headers by hand. Rather I want to supply a filename with the column labels in it to (presumably) the MySQL CREATE TABLE command. I'm using standard MySQL Query Browser tools in Ubuntu, but I didn't see in option for this in the create table dialog, nor could I figure out how to write a query to do this from the CREATE TABLE documentation page. But there must be a way...
A CREATE TABLE statement includes more than just column names
Table name*
Column names*
Column data types*
Column constraints, like NOT NULL
Column options, like DEFAULT, character set
Table constraints, like PRIMARY KEY* and FOREIGN KEY
Indexes
Table options, like storage engine, default character set
* mandatory
You can't get all this just from a list of column names. You should write the CREATE TABLE statement yourself.
Re your comment: Many software development frameworks support ways to declare tables without using SQL DDL. E.g. Hibernate uses XML files. YAML is supported by Rails ActiveRecord, PHP Doctrine and Perl's SQLFairy. There are probably other tools that use other format such as JSON, but I don't know one offhand.
But eventually, all these "simplified" interfaces are no less complex to learn as SQL, while failing to represent exactly what SQL does. See also The Law of Leaky Abstractions.
Check out SQLFairy, because that tool might already convert from files to SQL in a way that can help you. And FWIW MySQL Query Browser (or under its current name, MySQL Workbench) can read SQL files. So you probably don't have to copy & paste manually.
My question is how to store a nested JSON as key value in mysql table. Earlier I thought of storing it as CSV but on deep diving I found it like it would be difficult to query those values and to manage as well.
Please help me in giving alternate solutions of how and where to store JSON.
The version of MySQL I am using does not support the JSON data type
If you are using MySQL 5.7, you can store ans query JSON objects. Look at this link for more details and examples.
Since MySQL 5.7 a native JSON data type is supported.
See also https://dev.mysql.com/doc/refman/5.7/en/json.html
If your MySQL version is lower the only option left is to store it as text. Otherwise you will not be able to store it in a simple key value pair manner.