I know I can store images in mysql as data type blob. Wandering if i can compare the blob values in my query?
E.g. select answer from mtTable where imageBlobValue = image010.
Here imageBlobValue and image010 data type is blob.
TIA
Well, while that should be theoretically possible, a more optimal way to handle this would be to store an image hash or some other unique identifier alongside the blob to use for query purposes.
You want to minimize the amount of times the database has to handle that blob in memory and the best way to do that is to have a suitable key to search on.
Related
Which one is better: having a BLOB field in the same table or having a 1-TO-1 reference to it in another table?
I'm making a MySQL database whose main table is called item(ID, Description). This table is consulted by a program I'm developing in VB.NET which offers the possibility to double-click a specific item obtained with a query. Once opened its dedicated form, I would like to show an image stored in the BLOB field, a sort of item preview. The problem is I don't know where is better to create this BLOB field.
Assuming to have a table like this: Item(ID, Description, BLOB), will the BLOB field affect the database performance on queries like:
SELECT ID, Description FROM Item;
If yes, what do you think about this solution:
Item(ID, Description)
Images(Item, File)
Where Images.Item references to Item.ID, and File is the BLOB field.
You can add the BLOB field directly to your main table, as BLOB fields are not stored in-row and require a separate look-up to retrieve its contents. Your dependent table is needless.
BUT another and preferred way is to store on your database table only a pointer (path to the file on server) to your image file. In this way you can retrive the path and access the file from your VB.NET application.
To quote the documentation about blobs:
Each BLOB or TEXT value is represented internally by a separately allocated object. This is in contrast to all other data types, for which storage is allocated once per column when the table is opened.
In simpler terms, the blob's storage isn't stored inside the table's row, only a pointer is - which is pretty similar to what you're trying to achieve with the secondary table. To make a long story short - there's no need for another table, MySQL already doesn't the same thing internally.
Most of what has been said in the other Answers is mostly correct. I'll start from scratch, adding some caveats.
The two-table, 1-1, design is usually better for MyISAM, but not for InnoDB. The rest of my Answer applies only to InnoDB.
"Off-record" storage may happen to BLOB, TEXT, and 'large' VARCHAR and VARBINARY, almost equally.
"Large" columns are usually stored "off-record", thereby providing something very similar to your 1-1 design. However, by having InnoDB do the work usually leads to better performance.
The ROW_FORMAT and the size of the column makes a difference.
A "small" BLOB may be stored on-record. Pro: no need for the extra fetch when you include the blob in the SELECT list. Con: clutter.
Some ROW_FORMATs cut off at 767 bytes.
Some ROW_FORMATs store 20 bytes on-record; this is just a 'pointer'; the entire blob is off-record.
etc, etc.
Off-record is beneficial when you need to filter out a bunch of rows, then fetch only a few. Also, when you don't need the column.
As a side note, TINYTEXT is possibly useless. There are situations where the 'equivalent' VARCHAR(255) performs better.
Storing an image in the table (on- or off-record) is arguably unwise if that image will be used in an HTML page. HTML is quite happy to request the <img src=...> from your server or even some other server. In this case, a smallish VARCHAR containing a url is the 'correct' design.
I am new to web application developing. I am using php+mysql, so just wanted to check that what is best and safe way to create a database schema.
I have a table with 15 columns, the first column is unique id and remaining all are type of "text" and I am planning to put approx 1-20kb data in each column.
So is it good or bad or it should not be like that? So could anyone please help me on the same?
I am using engine type MYISAM.
The best idea depends on what you're using it for. VARCHAR is faster when the size is reasonable and also that is dependent on hardware and data that you are using. You should almost aways try to store text format messages as TEXT whereas string attributes as VARCHAR.
TEXT columns will not be stored in memory and will have to be read from the disk, which is much slower. Check this reference
Also check Blob Storage in Innodb
Dedicated data types exist for a reason. Some random things you can't do reliably (or can't do at all) with large blobs of text:
Maths
Date calculations
Proper indexes
Ensure a bare minimum of data integrity
Numeric sort
A database is much more than a dumb storage system.
Sometimes its must to use Text type. But try to use varchar instead od text/mediumtext/longtext etc. as often as its possible.
Usung text will have impact of performance.
Queries on text types are slower.
Data with text types will not be cached in memory.
I've got a single table DB with 100K rows. There are about 30 columns and 28 of them are varchars / tiny text and one of them is an int primary key and one of them is a blob.
My question, is in terms of performance, would it be better to separate the blob from the rest of the table and store them in their own table with foreign key constraint to the primary id?
The table will eventually be turned into a sqlite persistent store for iOS core data and a lot of the searching / filtering will be done based on the NSPredicate for the lighter varchar columns.
Sorry if this is too subjective, but I'm thinking there is a recommended way.
Thanks!
If you do SELECT * FROM table (which you shouldn't if you don't need the BLOB field actually) then yes, the query will be faster because in that case pages with BLOB won't be touched.
If you do frequent SELECT f1, f2, f3 FROM table (all fields are non-BLOBs) then yes, storing BLOBS in a separate table will make the query faster because of the same reason - MySQL will have to read less pages.
If however the BLOB is selected frequently then it makes no sense to keep it separately.
This totally depends on data usage.
If you need the data everytime you query the table, there is no difference in haviong a separate table for it (as long as blob data is unique in each row - that is, "as long as the database is normalized").
If you don'T need the blob data but only metadata from other columns, there may be a speed bonus qhen querying if the blob has its own table. querying the blob data is slower thoguh, as you need to query bowth tables.
The USUAL way is not to store any blob data inside the database (at least not huge data), but store the binary data into files and have the fiel path inside the database instead. This is recommended, as binary data most likely doesn'T benefit from being inside a DBMS (not indexable, sortable, groupable, ..), so there is no drawback of storing it inside files, while the database isn't optimized for binary data ('cause, again, it can't do much with it anyway).
Blobs are stored on disk only the point to the storage is in memory in Mysql. Moving it to another table with a foreign key will not noticeably help your performance. Don't know if this is the case for sqlite.
Part of my app includes volume automation for songs.
The volume automation is described in the following format:
[[0,50],[20,62],[48,92]]
I consider each item in this array a 'data point' with the first value containing the position in the song and the second value containing the volume on a scale of 0-100.
I then take these values and perform a function client-side to interpolate this data with 'virtual' data points in order to create a bezier curve allowing smooth volume transition as an audio file is playing.
However, the need has arisen to allow a user to save this automation into the database for recall at a later date.
The datapoints can be unlimited (though in reality should never really exceed around 40-50 with most being less than 10)
Also how should I handle the data? Should it be stored as is, in a text field? Or should I process it in some way beforehand for optimum results?
What data type would be best to use in MySQL to store an array?
Definitely not a text field, but a varchar -- perhaps. I wouldn't recommend parsing the results and storing them in individual columns unless you want to take advantage of that data in database sense -- statistics etc.
If you never see yourself asking "What is the average volume that users use?" then don't bother parsing it.
To figure out how to store this data ask yourself "How will i use it later?" If you will obtain the array and need to utilize it with PHP you can use serialize function. If you will use the values in JavaScript then JSON encoding will probably be best for you (plus many languages know how to decode it)
Good luck!
I suggest you to take a look at the JSON data type. This way you can store your array in a more efficient way than text or varchar, and you can access your data directly form MySQL without having to parse the whole thing.
Take a look at this link : https://dev.mysql.com/doc/refman/5.7/en/json.html
If speed is the most important when retrieving the rows then make a new table and make it dedicated to holding the indices of your array. Use the data type of integer and have each row represent an index of the array. You'll have to create another numeric column which binds these together so you can re-assemble the array with an SQL query.
This way you help MySQL help you speed up access. If you only want certain parts of the array, you just change the range in the SQL query and you can reassemble the array however you want.
The best way to store array is JSON data type -
CREATE TABLE example (
`id` int NOT NULL AUTO_INCREMENT,
`docs` JSON,
PRIMARY KEY (`id`)
);
INSERT INTO example (docs)
VALUES ('["hot", "cold"]');
Read more - https://sebhastian.com/mysql-array/#:~:text=Although%20an%20array%20is%20one,use%20the%20JSON%20data%20type.
I have a project where I need to store a large number of values.
The data is a dataset holding 1024 2Byte Unsigned integer values. Now I store one value at one row together with a timestamp and a unik ID.
This data is continously stored based on a time trigger.
What I would like to do, is store all 1024 values in one field. So would it be possible to do some routine that stores all the 1024 2byte integer values in one field as binary. Maybe a blobfield.
Thanks.
Br.
Enghoej
Yes. You can serialize your data into a byte array, and store it in a BLOB. 2048 bytes will be supported in a BLOB in most databases.
One big question to ask yourself is "how will I need to retrieve this data?" Any reports or queries such as "what IDs have value X set to Y" will have to load all rows from the table and parse the data AFAIK. For instance, if this were user configuration data, you might need to know which users had a particular setting set incorrectly.
In SQL Server, I'd suggest considering using an XML data type and storing a known schema, since this can be queried with XPath. MySQL did not support this as of 2007, so that may not be an option for you.
I would definitely consider breaking out any data that you might possibly need to query in such a manner into separate columns.
Note also that you will be unable to interpret BLOB data without a client application.
You always want to consider reporting. Databases often end up with multiple clients over the years.