I am using oracle xe,while creating columns it is created in upper case.Is there any rule to make the entire database columns in lower case.
To answer to your specific question: No
(you cannot globally change all column headings to lowercase)
Nonquoted Identifiers:
Unless you use quotes when creating objects the default for storage is upper case and these are called nonquoted identifiers in documentation. This allows "case insensitive" use of those names. e.g. a field stored with the name DESCRIPTION can be used in lowercase or mixed case like dEscRipTion
Quoted Identifiers
If however you use "quoted identifiers" then you create case sensitive names and all references to them must be a precise match. So a field with the stored name of DesCripTion must always be used with exactly that mixed case and DescripTion would not work.
In short, don't mess with the defaults, you are way better off leaving them as "nonquoted identifiers"
see: Schema Object Naming Rules
use oracle "rename" syntax.
for example:
// existing column on TABLE1 is CITY_NAME
// new name is cityName
// you can rename table and/or columns
rename table SCHEMA1.TABLE1 to "NewTableName"
and
rename column SCHEMA1.TABLE1.CITY_NAME to "cityName"
the main thing to remember is to enclose the new name in quotes.
you have to modify your exiting views and cursors because they will break.
Related
Inside my database I have some tables that use a column with a reserved word name for example user, I have created it using " as "USER" but when I want to get it I have realized that I have to put it in capital letters, I have already investigated and I obtained that when placing " oracle respects it as case sensitive, they somehow know how to avoid this and obtain my column without the need for it to be written as defined, that is, case insensitive.
I am working Oracle with Firedac, on the Firedac side, do you know if something can be done so that this can be solved by having to put the column name as it is?
No.
You chose to have a column that conflicts with a reserved word, so you had to quote it when you declared it. You also need to quote this identifier everytime you use it - and a quoted identifier is case-sensitive by design.
I would strongly suggest avoiding having column names that conflict with SQL reserved word (or keywords). There is no benefit, and many drawbacks. You could just rename that column to usr, username, userid, or else. Declare the new name as a unquoted identifier, and you will never need to worry about this all afterwards.
I want to create a database containing multiple tables using postgres 11 and i'm currently creating a table which contain brackets in the heading of the column (as shown as follows).
Table - supp_details
supp_id|supp_name | supp_weight(Kg)|
Can i add units to the heading and what is the proper way to do so with sql?
I'm a fresher to query writing, so please help me with this.
You could place the column name in quotes, e.g. use "supp_weight(Kg)", but it is best to avoid placing special characters or keywords as object names. Instead, I suggest using the following name:
supp_weight_kg
It is just a single string requiring no escaping, and makes it clear what the units are. A better option might be to just use supp_weight, and maybe just keep a note somewhere that the column uses kilograms as the unit by default.
You will need to use quoted identifiers but I strongly recommend not to do that:
create table supp_details
(
supp_id integer,
supp_name text,
"supp_weight(kg)" integer
);
Adding bracket symbols into your column names is possible but probably a bad idea. If you want to micromanage the name just for display purposes of the end result, you should probably do it in an alias, using the AS keyword.
SELECT supp_id, supp_name, supp_weight AS "supp_weight(Kg)" FROM ...
Or add the decorations on the client side before it displays the results.
I am facing an issue while fetching the data via query from a redshift table. For example:
table name: test_users
column names: user_id, userName, userLastName
Now while creating the test_users table it converts the capital letter of the userName column to username and similar with userLastName which will be converted to userlastname.
I have found the way to convert the all columns to capital or in lowercase, but not in the way to get it as it is.
Unfortunately, AWS Redshift does not support case-sensitive identifiers at the time of writing (Feb 2020). And, while Redshift is based on PostgreSQL, AWS has heavily modified it to the point where many assumptions that would be correct for PostgreSQL 8 are not correct for Redshift.
The documentation at https://docs.aws.amazon.com/redshift/latest/dg/r_names.html explicitly states that it downcases identifiers. The relevant paragraph is below, with the critical sentence bolded:
Names identify database objects, including tables and columns, as well as users and passwords. The terms name and identifier can be used interchangeably. There are two types of identifiers, standard identifiers and quoted or delimited identifiers. Identifiers must consist of only UTF-8 printable characters. ASCII letters in standard and delimited identifiers are case-insensitive and are folded to lowercase in the database. In query results, column names are returned as lowercase by default. To return column names in uppercase, set the describe_field_name_in_uppercase configuration parameter to true.
To preserve case:
SET enable_case_sensitive_identifier TO true;
https://docs.aws.amazon.com/redshift/latest/dg/r_enable_case_sensitive_identifier.html
To force returned uppercase fields (for anyone else curious):
SET describe_field_name_in_uppercase TO on;
https://docs.aws.amazon.com/redshift/latest/dg/r_describe_field_name_in_uppercase.html
create table ROOM
(NO_ROOM INT PRIMARY KEY, TYPE VARCHAR2(8) NOT NULL, SIZE VARCHAR2(8) NOT NULL)
;
I get ORA-00904, i think problem is from NO_ROOM. I try to use NUMBER, it's same.
PS. I make table for room that has no.room type and size.
SIZE is a reserved keyword. That means we cannot use it as an identifier (unless we put it in double quotes, but double-quoted identifiers are Teh Suck! so don't do that). Change the column name to ROOMSIZE and your statement will run.
Note that TYPE is also a keyword but not reserved. So we are allowed to use it as a column identifier. Types weren't introduced until 8; making TYPE a reserved keyword would have broken code in Oracle applications all over the world, not least in its own data dictionary.
The documentation has a complete list of the reserved words. Find it here.
Why would using "SIZE" be such a bad idea? After all, as #JavaBeginner says, the SQL standard does permit it.
Once we choose to use double-quotes to get around Oracle's naming rules we are condemned to use them whenever we reference the column. Hence this would not be a valid query:
select no_room, size
from room
where size > 10
We would have to write instead:
select no_room, "SIZE"
from room
where "SIZE" > 10
And it always have to be "SIZE": "size" is a different identifier. so is "Size".
Best practice is the informed interpretation of what the standards permit. SQL allows us to do things which we shouldn't do if we want to build a robust and maintainable database. Not using double-quoted identifiers falls into that category.
Size is a keyword and it cannot be used as column name unless you use it with double quotes. My suggestion is to use some other name for column as room_size. If you still want to use SIZE as column name for some reason, you will need to use double quotes while creating the table and also take care of the same while doing any other queries using this column.
Here is the working fiddle with size used as column name http://sqlfiddle.com/#!4/7e746
I do want to add(same as above) that using reserved word for column name(using double quotes) is a bad idea.
You can't use any of these reserved words as identifiers:
http://docs.oracle.com/cd/B19306_01/server.102/b14200/ap_keywd.htm
Size is in the list. If you choose another name for the column you should be okay.
SIZE is a reserved word by Oracle! So, it's not allowed to use them as a name of variables or objects. You can find here http://docs.oracle.com/cd/B28359_01/appdev.111/b31231/appb.htm list of reserved words for Oracle 11g.
Here is the second moment, you can use it inside double quote like "SIZE" or "Size", but that will be case sensitive and not recommended.
I tried to create table named 15909434_user with syntax like below:
CREATE TABLE 15909434_user ( ... )
It would produced error of course. Then, after I tried to have a bit research with google, I found a good article here that describe:
When you create an object in PostgreSQL, you give that object a name. Every table has a name, every column has a name, and so on. PostgreSQL uses a single data type to define all object names: the name type.
A value of type name is a string of 63 or fewer characters. A name must start with a letter or an underscore; the rest of the string can contain letters, digits, and underscores.
...
If you find that you need to create an object that does not meet these rules, you can enclose the name in double quotes. Wrapping a name in quotes creates a quoted identifier. For example, you could create a table whose name is "3.14159"—the double quotes are required, but are not actually a part of the name (that is, they are not stored and do not count against the 63-character limit). ...
Okay, now I know how to solve this by use this syntax (putting double quote on table name):
CREATE TABLE "15909434_user" ( ... )
You can create table or column name such as "15909434_user" and also user_15909434, but cannot create table or column name begin with numeric without use of double quotes.
So then, I am curious about the reason behind that (except it is a convention). Why this convention applied? Is it to avoid something like syntax limitation or other reason?
Thanks in advance for your attention!
It comes from the original sql standards, which through several layers of indirection eventually get to an identifier start block, which is one of several things, but primarily it is "a simple latin letter". There are other things too that can be used, but if you want to see all the details, go to http://en.wikipedia.org/wiki/SQL-92 and follow the links to the actual standard ( page 85 )
Having non numeric identifier introducers makes writing a parser to decode sql for execution easier and quicker, but a quoted form is fine too.
Edit: Why is it easier for the parser?
The problem for a parser is more in the SELECT-list clause than the FROM clause. The select-list is the list of expressions that are selected from the tables, and this is very flexible, allowing simple column names and numeric expressions. Consider the following:
SELECT 2e2 + 3.4 FROM ...
If table names, and column names could start with numerics, is 2e2 a column name or a valid number (e format is typically permitted in numeric literals) and is 3.4 the table "3" and column "4" or is it the numeric value 3.4 ?
Having the rule that identifiers start with simple latin letters (and some other specific things) means that a parser that sees 2e2 can quickly discern this will be a numeric expression, same deal with 3.4
While it would be possible to devise a scheme to allow numeric leading characters, this might lead to even more obscure rules (opinion), so this rule is a nice solution. If you allowed digits first, then it would always need quoting, which is arguably not as 'clean'.
Disclaimer, I've simplified the above slightly, ignoring corelation names to keep it short. I'm not totally familiar with postgres, but have double checked the above answer against Oracle RDB documentation and sql spec
I'd imagine it's to do with the grammar.
SELECT 24*DAY_NUMBER as X from MY_TABLE
is fine, but ambiguous if 24 was allowed as a column name.
Adding quotes means you're explicitly referring to an identifier not a constant. So in order to use it, you'd always have to escape it anyway.