When i execute SELECT * FROM tablename generate that erorr :
java.sql.SQLSyntaxErrorException: Table/View 'tablename' does not exist.
but if i run that sql command
SELECT * FROM "tablename" the sql run without problems why.
This is an aspect of the SQL standard known as "delimited identifiers".
Table names, column names, and other objects are things that you can give names to in your database.
The SQL standard says that, if you aren't particular about the upper/lower case of your object names, you can just specify the names without quotation marks, and your database will process them in a case-insensitive manner (typically, by converting an unquoted object name into the all-upper-case version of that name).
CREATE TABLE mytable(c1 INT, c2 CHAR(10));
INSERT INTO MyTable (C1, C2) VALUES (42, 'Bryan');
SELECT c2 FROM MYTABLE;
Since you didn't specify any object names in quotation marks, all of these examples work fine, because mytable, MyTable, and MYTABLE are all the same, when they aren't in quotation marks.
But if you specify your object names in quotation marks, then you have to get things exactly right:
CREATE TABLE "MyCaseSensitiveTable" (c1 int, c2 char(10));
INSERT INTO MyCaseInsensitiveTable (c1, c2) values (64, 'a nice age');
In this case, your INSERT statement will be rejected, because "MyCaseSensitiveTable" is different than MyCaseSensitiveTable.
Delimited identifiers bring other advantages:
You can use otherwise-reserved keywords from the SQL language as table names, so you can create a table named "TABLE" if you want.
You can use various special characters in your database object names.
Personally, I try never to use delimited identifiers, because I think they make my programs hard to read. But they are a completely legitimate part of the SQL standard and they are widely used.
But, the bottom line is: if you're going to put your database object names in quotation marks, you have to put them in quotation marks all the time, and you have to give the name exactly the same each time, but if you don't use quotation marks for your database object names, they will be treated in a case-insensitive manner.
Related
I have a column in my database table named UID. For some reason queries fail unless I surround the column name with double quotation marks (" "). None of the other columns require these quotation marks.
For example, this doesn't work:
SELECT user_name FROM user_table WHERE UID = '...'
But this does:
SELECT user_name FROM user_table WHERE "UID" = '...'
Is UID some kind of keyword? Why is it only happening to that column? How do I know if I need to use double quotes for other columns?
By the way, I'm running JDK 1.8_221 and using an oracle JDBC driver if that makes a difference.
Yes, it is about keywords. You can double quote everything (tables, columns) to avoid this but I can understand you don't want to do this.
To have a list of standard keywords: SQL Keywords
But you can see UID is not in this list as I assume it is a reserved keyword by your database implementation. I had the same problem with a table called "order" as it contains orders. ORDER is a keyword so I had to quote it each time.
So best is to test your statements using a SQL client tool.
Since you mention Oracle: Oracle keywords: "You can obtain a list of keywords by querying the V$RESERVED_WORDS data dictionary view."
If your create table command for user_table looks something like this:
create table user_table ("UID" varchar2(10))
then you will have to use quotes around UID in your query. This query:
select * from user_table where UID = 'somestring'
means to use the Oracle predefined UID pseudo column and your table's UID column will not be accessed.
If your table doesn't have a user-defined UID column, then using "UID" should fail.
My guess is your table does indeed have a UID column and when you say it "doesn't work" without using the quotes you probably mean it motivates an ORA-1722.
The type of failure, when using UID without quotes, depends on the content of the string 'somestring'. If the content of that string can be cast as a number then you probably won't get the rows you expect. If it cannot be cast as a number then you'll get an ORA-1722.
As an aside, if you try to execute this, then you'll get an ORA-904:
create table user_table (UID number)
Yes, it is keywords and return
UID returns an integer that uniquely identifies the session user (the
user who logged on).
By default, Oracle identifiers (table names, column names, etc.) are case-insensitive. You can make them case-sensitive by using quotes around them when creating them (eg: SELECT * FROM "My_Table" WHERE "my_field" = 1). SQL keywords (SELECT, WHERE, JOIN, etc.) are always case-insensitive.
You can use it for more information here.
I have a script in ASP Classic that uses a Firebird database. I would like to execute a query without "quotation marks"
Now I must write this:
SQL = "SELECT ""TArticoli"".""IDArticolo"",""TArticoli"".""Desc"" FROM ""TArticoli"";"
I would write this:
SQL = "SELECT TArticles.IDArticle, TArticles.Desc FROM TArticles;"
The first one is accepted the second not, how can I do this?
You can't. DESC is a reserved word in Firebird, so to be able to use it as a column name (or any other object name for that matter), you will need to enclose it in quotes.
A second problem is that you are currently using
SELECT "TArticoli"."IDArticolo","TArticoli"."Desc" FROM "TArticoli"
And this means both your table name and the column names are case sensitive, and in that case, quoting those object names is mandatory. Unquoted object names are case insensitive, but are mapped to object names in upper case. This means that select * from TArticoli will select from a table called TARTICOLI, while select * from "TArticoli", selects from a table called TArticoli.
So unless you are going to rename or recreate all your tables or columns, you will not be able to get rid of quotes. The only thing you can do to reduce the number of quotes, is by not prefixing the columns with the table names (in the query shown it isn't necessary), or otherwise use a case insensitive alias for the table, eg
SELECT "IDArticolo", "Desc" FROM "TArticoli"
or
SELECT a."IDArticolo", a."Desc" FROM "TArticoli" AS a
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.
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 do the brackets do in a sql statement?
For example, in the statement:
insert into table1 ([columnname1], columnname2) values (val1, val2)
Also, what does it do if the table name is in brackets?
The [] marks the delimitation of a identifier, so if you have a column whose name contains spaces like Order Qty you need to enclose it with [] like:
select [Order qty] from [Client sales]
They are also to escape reserved keywords used as identifiers
This is Microsoft SQL Server nonstandard syntax for "delimited identifiers." SQL supports delimiters for identifiers to allow table names, column names, or other metadata objects to contain the following:
SQL reserved words: "Order"
Words containing spaces: "Order qty"
Words containing punctuation:
"Order-qty"
Words containing international
characters
Column names that are
case-sensitive: "Order" vs. "order"
Microsoft SQL Server uses the square brackets, but this is not the syntax standard SQL uses for delimited identifiers. Standardly, double-quotes should be used for delimiters.
In Microsoft SQL Server, you can enable a mode to use standard double-quotes for delimiters as follows:
SET QUOTED_IDENTIFIER ON;
They are meant to escape reserved keywords or invalid column identifiers.
CREATE TABLE test
(
[select] varchar(15)
)
INSERT INTO test VALUES('abc')
SELECT [select] FROM test
They allow you to use keywords (such as date) in the name of the column, table, etc...
Since this is a bad practice to begin with, they are generally not included. The only place you should see them being used is by people starting out with sql queries that don't know any better. Other than that they just clutter up your query.
Anything inside the brackets is considered a single identifier (e.g. [test machine]. This can be used to enclose names with spaces or to escape reserve words (e.g. [order], [select], [group]).
if you use any column name which is same as any reserved keyword in sql, in that case you can put the column name in square bracket to distinguish between your custom column name and existing reserved keyword.
When having table names or filenames with spaces or dashes (-) etc... you can receive "Systax error in FROM clause".
Use [] brackets to solve this.
See: https://msdn.microsoft.com/en-us/library/ms175874.aspx
They are simply delimiters that allow you to put special characters (like spaces) in the column or table name
e.g.
insert into [Table One] ([Column Name 1], columnname2) values (val1, val2)