Unless you're at the point where preventing the DB from performing a length check on data it receives is going to provide a tangible benefit this article is awful advice. The good thing about this approach is that limit change is instant – you just do “CREATE OR REPLACE FUNCTION", and you're done. 2. What the benchmarks show, if anything, is that while the `check` involves negligible overhead per row, the overhead can eventually be enough to make a measurable difference. IMHO always use the right field for the job.. Surprised someone hasn't pointed out, too, that catching this in code is faster/cheaper than a database hit and erroring back to the front end. AFAIR, MySQL. Merge join: Sort both sets of rows and merge them. Users figured out they could upload really big files and harm the system. But if there is multiple interfaces (such as a REST api etc) to your database then you have to remember to put them in place everywhere. Plus lots of us still have to write apps that actually read old files too - CHAR is appropriate for these as well, assuming you are storing fields that aren't right-padded in the source datafile (such as social security numbers, etc.). In addition, PostgreSQL provides the text type, which stores strings of any length. What’s drawback if they want to the title up to 80 chars! Also a lot of application frameworks that interact with the database only deal with VARCHAR so then as soon as you use a CHAR you have to start worrying about trimming your text data because one of the biggest database text type gotchas is accidentally trying to compare a VARCHAR and a CHAR improperly. Results are promising and aligned with your findings. (Yes that is hilariously bad.) As an example, if you look at the documentation page for strings in PostgreSQL (they've been natively UTF-8 based for a long time), they say: Both char(n) and varchar(n) can store up to n … 2. (which, fwiw, was written by someone who likely knows more than is healthy about RDBMS implementations of SQL). The explanation was provided for the benefit of other readers than myself and the parent poster. > As the PG docs say, there is virtually no performance difference at all between all three. Interesting, I was just thinking about a variable width item on the disk expanding or contracting, and if it had to be arranged in a serial physical order it would (necessarily) be forced to move the other bits if it wasn't inserted at the end. Yes, because varchar is implemented as a fixed-length list of characters. What type you use also tells you something about the kind of data that will be stored in it (or we'd all use text for everything).If something has a fixed length, we use char. Uh, shouldn't you use the most appropriate type available to describe your data, since that will simplify the process if you ever need to migrate to a different DBMS? For varchar you just make an array, because all values are the same length. multiple interfaces going directly to database - that's a much bigger problem that the rest pales before it. If you want an actual fixed length of non-blank data you need an additional check constraint to enforce the min-length. Everything that can happen repeatedly put a high limit on it and raise or lower the limit as needed. Well, just before I ran this transaction I ran this SQL: Afterwards, the numbers are the same, so table was not rewritten. Joins are usually implemented in one of these three ways, and the planner can select which one to use depending on the query and table statistics: 1. I say it's not what people expect because everyone emphasizes the "fixed length" rather than "blank padded" nature of CHAR. I have two systems with different hardware and OSs. Just define a column constraint (syntax might be wrong): Doesn't the use of check constraints add an overhead and possibly negate the slight performance advantage that was gained by using text instead of varchar/char? I've used PostgresSQL quite successfully for the past few years at rather large scales and I can tell you, using TEXT everywhere is sooooooooo much easier on everyone involved. But if there is multiple interfaces (such as a REST api etc) to your database then you have to remember to put them in place everywhere. As someone who regularly has to write SQL in 7 different dialects I much prefer VARCHAR to TEXT as the former is handled much more consistently across platforms. Character type is pretty simple. What if the performance changes? The padding behavior is nothing new, and is intuitive - the value must be N characters in length, so if you stored less, you get back a right-padded string. So, we know that storing the data takes the same time. If you need a TEXT field to store data that could be large, then do it. Especially on large teams (hundreds of developers) where migrations are a big deal. Whether migrating a database or an application from DB2 to PostgreSQL with only one type of database knowledge is not sufficient, there are few things to know about the differences between the two database systems.. PostgreSQL is world’s most widely used advanced open source database. Postgresql Varchar Vs Text Storage Space Articles & Shopping. That layer is called postgresql. Then chances are your VARCHAR will not work anyway because while VARCHAR exists everywhere its semantics and limitations change from one DB to the next (Postgres's VARCHAR holds text, its limit is expressed in codepoints and it holds ~1GB of data, Oracle and SQL Server's are bytes and have significantly lower upper bounds (8000 bytes IIRC)). Is that all that we can do? PostgreSQL Database Forums on Bytes. Is anything really fixed-length? Those people change their minds ALL THE TIME ("Yeah, I know we agreed that we only need about 20 characters for the description here, but we now think 25 will really make the whole thing pop, ya know?"). If you do have different length then a VARCHAR is more appropriate. use VARCHAR because constraints are a good thing, and use CHAR if you are storing strings of a fixed length, because semantics are a good thing. Longer strings have 4 bytes of overhead instead of 1. VARCHAR (without the length specifier) and TEXT are equivalent. If adding a column or expanding a field takes O(n) time, don't expect n to be small forever. Constraints might stops users from creating extremely large records but they won't stop users from creating an extremely large number of records etc. Additionally, one of the key benefits of more explicit datatypes is documentation. And I know that mainframes still exist but they aren't the use case in mind when many say "USE CHAR". From what I know, you can't do that in SQL Server/Oracle, you can only use full text searching (I think). Any remarks? For example, PosgtgreSQL's VARCHAR type has different semantics from Oracle's: One supports Unicode and the other doesn't. But don't make your "username" field a TEXT when VARCHAR(300) would do. If every text column is TEXT then that's much less clear. Don’t accept huge text blobs either. I don't see a good reason to make a username field to be TEXT instead of a generous VARCHAR(300). Lets Postgre do that for you. Yang terakhir adalah ekstensi PostgreSQL. No, they're not, that's why it's a VARCHAR and not just a CHAR. Inserting 'a' into a CHAR(2) results in 'a ' being stored and retrieved from the database. But how a ‘cat’ becomes a CHAR(8). Pietro, Now we have description of this question in PostgreSQL manual: http://www.postgresql.org/docs/9.1/static/datatype-character.html, "Testing of: create table, load data and create index. Use Char data type if the length of the string you are storing is fixed for all the rows in the column. Why? Now, let's add check, so we will have something to alter . A domain using a TEXT field and constraints is probably the most performant (and flexible). Across speed requirements? Use VARCHAR(n) if you want to validate the length of the string (n) before inserting into or updating to a column. So basically on each system I had two schemas that differed only about text/non-text columns. > What if you decide to migrate to a different db at a later time? Consider a table named TEXTS in order to understand the examples of the PostgreSQL VARCHAR data type. I would love if someone has a good article comparing what happens when you do a join on varchar vs text. If you care about semantics you should create a domain based on VARCHAR. Let's test. Not to mention that boring things like state codes, country codes, and the like are often fixed length fields. 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