What is the best way to store a large amount of text in a table in SQL server?
Is varchar(max) reliable?
In SQL 2005 and higher, VARCHAR(MAX) is indeed the preferred method. The TEXT type is still available, but primarily for backward compatibility with SQL 2000 and lower.
I like using VARCHAR(MAX) (or actually NVARCHAR) because it works like a standard VARCHAR field. Since it's introduction, I use it rather than TEXT fields whenever possible.
Varchar(max) is available only in SQL 2005 or later. This will store up to 2GB and can be treated as a regular varchar. Before SQL 2005, use the "text" type.
According to the text found here, varbinary(max) is the way to go. You'll be able to store approximately 2GB of data.
Split the text into chunks that your database can actually handle. And, put the split up text in another table. Use the id from the text_chunk table as text_chunk_id in your original table. You might want another column in your table to keep text that fits within your largest text data type.
CREATE TABLE text_chunk (
id NUMBER,
chunk_sequence NUMBER,
text BIGTEXT)
In a BLOB
BLOBs are very large variable binary or character data, typically documents (.txt, .doc) and pictures (.jpeg, .gif, .bmp), which can be stored in a database. In SQL Server, BLOBs can be text, ntext, or image data type, you can use the text type
text
Variable-length non-Unicode data, stored in the code page of the server, with a maximum length of 231 - 1 (2,147,483,647) characters.
Depending on your situation, a design alternative to consider is saving them as .txt file to server and save the file path to your database.
Use nvarchar(max) to store the whole chat conversation thread in a single record. Each individual text message (or block) is identified in the content text by inserting markers.
Example:
{{UserId: Date and time}}<Chat Text>.
On display time UI should be intelligent enough to understand this markers and display it correctly. This way one record should suffice for a single conversation as long as size limit is not reached.
Related
I am moving a table from SQL Server to Redshift. I've exported the data and gotten it into a UTF-8 text file. When trying to load to Redshift, the COPY command fails, complaining the data exceeds the width of the field.
The destination Redshift table schema matches that of the source SQL Server table (i.e. varchar field widths are the same). If I understand correctly, Redshift's varchar size is in bytes, not characters, like SQL Server. So, multi-byte characters are causing the "too wide" problem.
I'd like to run a query to determine how big to make my varchar fields, but there doesn't seem to be a function that returns the number of bytes a string requires, only the number of characters in that string.
How have others solved this problem?
Field length and as consequence fields types might be critical in Redshift. Load sample data into RedShift table with maximum fields sizes. Sample has to be as big as possible. Than you will be be able to calculate real field sizes with disregard of the definitions in MSSQL Server, that might be much bigger than you really need.
I have been asked to code an SQL table that has a comment field that:
must be able to store at least several pages of text
What data type should I use, and what value equates to several pages of text?
In MS SQL varchar(max) stores a maximum of 2 147 483 647 characters
Depending on the Database you are using, there are Text or CLOB (character large object), which you should use for the column with the several pages of text.
The reason for this is, that the content of these columns are stored somewhere else in the database system (out-of-line) and don't decrease performance on other operations on this table (like e.g. aggregation of some statistaical data).
How long does an nvarchar field need to be before it is better to use a text field in SQL Server? What are the general indications for using one or the other for textual content that may or may not be queried?
From what I understand, the TEXT datatype should never be used in SQL 2005+. You should start using VARCHAR(MAX) instead.
See this question about VARCHAR(MAX) vs. TEXT.
UPDATE (per comment):
This blog does a good job at explaining the advantages. Taken from it:
But the pain from using the type text comes in when trying to query against it. For example grouping by a text type is not possible.
Another downside to using text types is increased disk IO due to the fact each record now points to a blob (or file).
So basically, VARCHAR(MAX) keeps the data with the record, and gives you the ability to treat it like other VARCHAR types, like using GROUP BY and string functions (LEN, CHARINDEX, etc.).
For TEXT, you almost always have to convert it to VARCHAR to use functions against it.
But back to the root of your question regarding efficiency, I don't think it's ever more efficient to use TEXT vs. VARCHAR(MAX). Looking at this MSDN article (search for "data types"), TEXT is deprecated, and should be replaced with VARCHAR(MAX).
First of all don't use text at all. MSDN says:
ntext, text, and image data types will
be removed in a future version of
Microsoft SQL Server. Avoid using
these data types in new development
work, and plan to modify applications
that currently use them. Use
nvarchar(max), varchar(max), and
varbinary(max) instead.
varchar(max) is what you might need.
If you compare varchar(n) vs varchar(max), these are technically two different datatypes (stored differently):
varchar(n) value is always stored inside of the row. Which means it cannot be greater than max row size, and row cannot be greater than page size, which is 8K.
varchar(max) is stored outsize the row. Row has a pointer to a separate BLOB page. However, under certain condition varchar(max) can store data as a regular row, obviously it should at least fit to the row size.
So if your row is potentially greater than 8K, you have to use varchar(max). If not, using varchar(n) will likely be preferable as it is faster to retrieve in-row data vs from outside page.
MSDN says:
Use varchar(max) when the sizes of the
column data entries vary considerably,
and the size might exceed 8,000 bytes.
The main advantage of VARCHAR over TEXT is that you can run string manipulations and string functions on it. With VARCHAR(max), now you basically have an awesome large (unrestricted) variable that you can manipulate how you want..
I have 2 columns containing text one will be max 150 chars long and the other max 700 chars long,
My question is, should I use for both varchar types or should I use text for the 700 chars long column ? why ?
Thanks,
The varchar data type in MySQL < 5.0.3 cannot hold data longer than 255 characters. While in MySQL >= 5.0.3 it has a maximum of 65,535 characters.
So, it depends on the platform you're targeting, and your deployability requirements. If you want to be sure that it will work on MySQL versions less than 5.0.3, go with a text type data field for your longer column
http://dev.mysql.com/doc/refman/5.0/en/char.html
An important consideration is that with varchar the database stores the data directly in the table, and with text the database stores a pointer to a separate tablespace in which the data is stored. So, unless you run into the limit of a row length (64K in MySQL, 4-32K in DB2, 8K in SQL Server 2000) I would normally use varchar.
Not sure about mysql specifically, but in MS SQL you definitely should use a VARCHAR for anything under 8000 characters long, if you want to be able to run any sort of comparison on the value in the field. For example this would be possible with a VARCHAR:
select your_column from your_table
where your_column like '%dogs%'
but not with a TEXT field.
More information regarding TEXT field in mysql 5.4 can be found here and more information about the VARCHAR field can be found here.
I'd pick the option based on the type of data being entered. For example, if it's a (potentially) super long username and a biography, I'd do varchar and text. Sure, you're limiting the bio to 700 chars, but what if you add HTML formatting down the road, keeping the 700 char limit but allowing HTML tags for formatting?
Twitter may use text for their tweets, since it could be quicker to add meta data to the posts (e.g. url href's and #user PK's) to cache the additional data instead of caluclate it every rendering.
Suppose I have a bunch of varchar(6000) fields in a table and want to change those to text fields. What are the ramifications of the stored procedures whose arguments are of type varchar(6000). Does each stored procedure also need those argument data types changed?
Text fields are deprecated in SQL Server 2005 and above. You should use varchar(MAX), if possible. If you expect to have more than 6000 characters passed in the arguments to your stored procedures, you will need to change them as well.
Text fields are rough to work with in SQL Server. You can't actually declare local variables of type text (except as parameters to a stored procedure) and most of the string manipulation functions no longer work on text fields.
Also if you have triggers the text fields will not appear on the INSERTED or DELETED tables.
Basically if the field is just holding data from a program and you aren't manipulating it then no big deal. But if you have stored procedures to manipulate the string then your task will be way more difficult.
As tvanfosson mentioned if you have SQL Server 2005 use VARCHAR(MAX) then you get the length of a text field with the ability to manipulate it like it is a VARCHAR.
The other answers are right, but they don't answer your question. Varchar(max) is the way to go. If you made the feilds varchar(max)/text, but kept the stored proc arguments the same, any field that came in through the stored proc would be truncated to 6000 characters. Since you say that it will never exceed that, you will be fine, until, of course, that isn't the case. It doesn't throw an error. It just truncate.
I'm not sure of the exact behavior of varchar(max) verses text, but I'm pretty sure that once you start putting a lot of them in one table, you can get some crazy performance hits. Why so many big fields in one table?
The reason for text field usage is that all of the varchar(6000) fields in one row exceed the max row length. Text fields just store a pointer in the row thus not exceeding the SQL Server max row length of 8000 something. ATM the database cannot be normalized. The data is not manipulated by the stored procedures it's just inserted, updated and deleted.
Does VARCHAR(MAX) behave like a text field and only store a pointer to the data in the row?