This question is based on this answer.
What does the following sentence mean?
Finally, don't use mixed case
identifiers. Do everything lowercase,
so you don't have to quote them.
Does it mean that I should change the commands such as CREATE TABLE, USER_ID and NOT NULL to lowercase? - It cannot because it would be against common naming conventions.
In PostgreSQL, an unquoted identifier is converted into lowercase:
CREATE TABLE "MYTABLE" (id INT NOT NULL);
CREATE TABLE "mytable" (id INT NOT NULL);
INSERT
INTO "MYTABLE"
VALUES (1);
INSERT
INTO "mytable"
VALUES (2);
SELECT *
FROM mytable;
---
2
SELECT *
FROM MYTABLE;
---
2
Both queries will return 2, since they are issued against "mytable", not "MYTABLE".
To return 1 (i. e. issue a query against "MYTABLE", not "mytable"), you need to quote it:
SELECT *
FROM "MYTABLE";
---
1
CREATE TABLE etc. are not identifiers, they are reserved words.
You can use them in any case you like.
No, I think the gentleman referred to using all lowercase identifiers, e.g. table, column etc. names. This should have no impact on the commands like CREATE TABLE etc. that you use.
Marc
I have no idea why he said that. In SQL Server, at least, the case of an identifier doesn't matter. Maybe it does in other DBMS systems?
Related
I have created a table in Oracle 10g using the following CREATE statement.
CREATE TABLE test ("id" NUMBER(35, 0) primary key, "description" VARCHAR2(250) not null);
The basic table structure looks like as follows.
--------------------------------------------------------------------------------
Column Name Data Type Nullable Default Primary Key
--------------------------------------------------------------------------------
id NUMBER(35, 0) No - 1
description VARCHAR2(250) No - -
It should precisely be noted that the column names in this CREATE statement are enclosed within double quotes just for having a fun :)
After issuing this DDL statement, I issued three DML statements to add this many rows as follows.
INSERT INTO test VALUES (1, 'aaa');
INSERT INTO test VALUES (2, 'bbb');
INSERT INTO test VALUES (3, 'ccc');
And finally, the following SELECT statement was executed to verify, if those rows were inserted.
SELECT * FROM test;
Oracle indeed displays three rows exactly as inserted on executing this query.
But when I issue the following SELECT query,
SELECT id, description FROM test;
Oracle complains,
ORA-00904: "DESCRIPTION": invalid identifier
The following (same) query also,
SELECT id FROM test;
fails with the error,
ORA-00904: "ID": invalid identifier
The same is true for the query,
SELECT description FROM test;
The only SELECT query with the meta character * works. Listing fields in the SELECT clause doesn't work. Capitalizing the column names in the SELECT clause also doesn't work.
What is the reason behind it?
Please don't just say, Don't do this. I'm interested in knowing the reason behind it.
OK, I won't say it, I'll just think it loudly.
The documentation clearly says that if you have quoted identifiers, you have to quote them everywhere (my italics for emphasis):
Every database object has a name. In a SQL statement, you represent the name of an object with a quoted identifier or a nonquoted identifier.
A quoted identifier begins and ends with double quotation marks ("). If you name a schema object using a quoted identifier, then you must use the double quotation marks whenever you refer to that object.
A nonquoted identifier is not surrounded by any punctuation.
So you always have to do:
SELECT "id", "description" FROM test;
Which is a pain. But obviously I'm just thinking that too, not really saying it.
I have a db table say, persons in Postgres handed down by another team that has a column name say, "first_Name". Now am trying to use PG commander to query this table on this column-name.
select * from persons where first_Name="xyz";
And it just returns
ERROR: column "first_Name" does not exist
Not sure if I am doing something silly or is there a workaround to this problem that I am missing?
Identifiers (including column names) that are not double-quoted are folded to lowercase in PostgreSQL. Column names that were created with double-quotes and thereby retained uppercase letters (and/or other syntax violations) have to be double-quoted for the rest of their life:
"first_Name"
Values (string literals / constants) are enclosed in single quotes:
'xyz'
So, yes, PostgreSQL column names are case-sensitive (when double-quoted):
SELECT * FROM persons WHERE "first_Name" = 'xyz';
Read the manual on identifiers here.
My standing advice is to use legal, lower-case names exclusively so double-quoting is never required.
To quote the documentation:
Key words and unquoted identifiers are case insensitive. Therefore:
UPDATE MY_TABLE SET A = 5;
can equivalently be written as:
uPDaTE my_TabLE SeT a = 5;
You could also write it using quoted identifiers:
UPDATE "my_table" SET "a" = 5;
Quoting an identifier makes it case-sensitive, whereas unquoted names are always folded to lower case (unlike the SQL standard where unquoted names are folded to upper case). For example, the identifiers FOO, foo, and "foo" are considered the same by PostgreSQL, but "Foo" and "FOO" are different from these three and each other.
If you want to write portable applications you are advised to always quote a particular name or never quote it.
The column names which are mixed case or uppercase have to be double quoted in PostgresQL. So best convention will be to follow all small case with underscore.
if use JPA I recommend change to lowercase schema, table and column names, you can use next intructions for help you:
select
psat.schemaname,
psat.relname,
pa.attname,
psat.relid
from
pg_catalog.pg_stat_all_tables psat,
pg_catalog.pg_attribute pa
where
psat.relid = pa.attrelid
change schema name:
ALTER SCHEMA "XXXXX" RENAME TO xxxxx;
change table names:
ALTER TABLE xxxxx."AAAAA" RENAME TO aaaaa;
change column names:
ALTER TABLE xxxxx.aaaaa RENAME COLUMN "CCCCC" TO ccccc;
You can try this example for table and column naming in capital letters. (postgresql)
//Sql;
create table "Test"
(
"ID" integer,
"NAME" varchar(255)
)
//C#
string sqlCommand = $#"create table ""TestTable"" (
""ID"" integer GENERATED BY DEFAULT AS IDENTITY primary key,
""ExampleProperty"" boolean,
""ColumnName"" varchar(255))";
Is there a difference between the following two queries?
CREATE TABLE alpha(age INTEGER);
and
CREATE TABLE alpha("age" INTEGER);
I read that database objects are case INSENSITIVE unless they are kept in quotation marks.
This applies when I try to keep the TABLE object in quotation marks but isn't working for the attributes.
I guess the reason is attributes are not database objects. Is this correct?
If yes, then in what category does attributes fall under, if not database object?
Is there a difference ? yes.
when you don't use quotes, like:
CREATE TABLE alpha(age INTEGER);
oracle will store that column and table as UPPERCASE in the data dictionary.
in other words , these statements are identical:
CREATE TABLE alpha(age INTEGER);
CREATE TABLE "ALPHA"("AGE" INTEGER);
CREATE TABLE ALPHA(AGE INTEGER);
Also, any subsequent dml/ddl on the table like:
select age from alpha;
would be first converted to uppercase when looking up the object/column; so the above SQL would work fine. i.e oracle would look for the column AGE and the table ALPHA and not the column age or the table alpha as was typed.
however, when you create with a quoted identifier:
CREATE TABLE alpha("age" INTEGER);
oracle would create table ALPHA with a column in lowercase age (check user_tab_columns to see this). so ONLY the following would work to select it:
select "age" from alpha;
select "age" from "ALPHA";
select "age" from ALPHA;
and not:
select age from alpha;
eg:
http://sqlfiddle.com/#!4/3084e/1
It depends on the database engine, and even how the database itself or the connected session is configured. However, in general, SQL Server would treat age and "age" as the same identifier, while Oracle would consider age and "age" to be different.
In regard to attributes (columns), treatment of those identifiers vary widely as well. Most database engines will allow the attributes to be identified by quotation marks (or other delimiters) and in the same way the table identifiers are handled.
Is it possible to create a table with column name containing space? If so how can I create and use it?
It is possible, but it is not advisable. You need to enclose the column name in double quotes.
create table my_table ("MY COLUMN" number);
But note the warning in the documentation:
Note: Oracle does not recommend using quoted identifiers for database
object names. These quoted identifiers are accepted by SQL*Plus, but
they may not be valid when using other tools that manage database
objects.
The name will be case-sensitive, and you wil have to enclose the name in double quotes every time you reference it:
select "MY COLUMN" from my_table;
So... don't, would be my advice...
Yes, it's possible. You just have to be sure to quote the column name. For instance:
CREATE TABLE Fubar ("Foo Bar" INT);
INSERT INTO Fubar VALUES (1337);
SELECT "Foo Bar" FROM SpaceMonster
Even though it's possible, it doesn't make it a good idea. You'll probably save yourself from a lot of pain if just replace all you spaces with underscores.
it is possible by naming the column between two "
example: "My columN" , the column name becomes case sensitive which means.
SELECT "my column" from table; --NOT OK
SELECT "My columN" from table; --OK
You can (see the Oracle doc) if you quote these appropriately. However I suspect this is not a good idea, since you'll have to quote everything. Generally db naming standards / conventions (e.g. here or here) favour using underscores (which don't require quoting) over whitespace.
This is the columns rule defined for oracle
Columns (for tables)
All columns are in form {alias}_{colname}. For example prs_id,
prs_name, prs_adr_id, adr_street_name. This guarantees that column
names are unique in a schema, except denormalized columns from
another table, which are populated using triggers or application
logic.
All columns are in singular. If you think you need a column name in plural think twice whether it is the right design? Usually it
means you are including multiple values in the same column and that
should be avoided.
All tables have surrogate primary key column in form {alias}_id, which is the first column in the table. For example, prs_id, mat_id,
adr_id.
you can always have alias for column name bu using ""
Did you Google for this? I did - the 6th link was this, in which I find the following:
create table employee (
"First Name" varchar2(20),
"Last Name" varchar2(20),
Address varchar2(60),
Phone varchar2(15),
Salary number,
EmpID number,
DeptID number
);
... which works fine when I tried it in 10g.
What are the combination of characters for a table name in SQLite to be valid? Are all combinations of alphanumerics (A-Z, a-z and 0-9) constitute a valid name?
Ex. CREATE TABLE 123abc(...);
What about a combination of alphanumerics with dashes "-" and periods ".", is that valid as well?
Ex. CREATE TABLE 123abc.txt(...);
Ex. CREATE TABLE 123abc-ABC.txt(...);
Thank you.
I haven't found a reference for it, but table names that are valid without using brackets around them should be any alphanumeric combination that doesn't start with a digit:
abc123 - valid
123abc - not valid
abc_123 - valid
_123abc - valid
abc-abc - not valid (looks like an expression)
abc.abc - not valid (looks like a database.table notation)
With brackets you should be able to use pretty much anything as a table name:
[This should-be a_valid.table+name!?]
All of these are allowed, but you may have to quote them in "".
sqlite> CREATE TABLE "123abc"(col);
sqlite> CREATE TABLE "123abc.txt"(col);
sqlite> CREATE TABLE "123abc-ABC.txt"(col);
sqlite> select tbl_name from sqlite_master;
123abc
123abc.txt
123abc-ABC.txt
In general, though, you should stick to the alphabet.
Per Clemens on the sqlite-users mailing list:
Everything is allowed, except names beginning with "sqlite_".
CREATE TABLE "TABLE"("#!#""'☺\", "");
You can use keywords ("TABLE"), special characters (""#!#""'☺\"), and even the empty string ("").
From SQLite documentation on CREATE TABLE, the only names forbidden are those that begin with sqlite_ :
Table names that begin with "sqlite_" are reserved for internal use. It is an error to attempt to create a table with a name that starts with "sqlite_".
If you use periods in the name you will have issues with your SQL Queries. So I would say avoid those.