I'm only beginning to learn SQL with SQLite3 so this question probably has a clear answer, which I just can't think of. I have a table called Books, which has the columns: name, author and price. When I type e.g. select name, price from Books where author = "A"; in sqlite3, it works just fine. However, when I make a .sql file with the following:
SELECT name, price
FROM Books
WHERE author = "A";`
and read the file in the same database, it reads
'Error: near line 1: no such column: "A"'
Any ideas?
Edit: I have also tried the same with single quotes (i.e. 'A') but it still gives the same error:
Error: near line 1: no such column: 'A'
Double quotes "A" are used as identifiers; you want to use single quotes 'A' for string literals. See the documentation for more information.
SELECT name, price FROM Books WHERE author = 'A';
The reason it worked in the first example is probably due to this:
If a keyword in double quotes (ex: "key" or "glob") is used in a
context where it cannot be resolved to an identifier but where a
string literal is allowed, then the token is understood to be a string
literal instead of an identifier.
I found the solution. I was using Mac's TextEdit program to write the SQL queries and it uses so called "smart quotes", which are not recognized as quotes by SQL. So I just changed the smart quote-setting off and all is well.
Related
One of my columns is called from. I can't change the name because I didn't make it.
Am I allowed to do something like SELECT from FROM TableName or is there a special syntax to avoid the SQL Server being confused?
Wrap the column name in brackets like so, from becomes [from].
select [from] from table;
It is also possible to use the following (useful when querying multiple tables):
select table.[from] from table;
If it had been in PostgreSQL, use double quotes around the name, like:
select "from" from "table";
Note: Internally PostgreSQL automatically converts all unquoted commands and parameters to lower case. That have the effect that commands and identifiers aren't case sensitive. sEleCt * from tAblE; is interpreted as select * from table;. However, parameters inside double quotes are used as is, and therefore ARE case sensitive: select * from "table"; and select * from "Table"; gets the result from two different tables.
These are the two ways to do it:
Use back quote as here:
SELECT `from` FROM TableName
You can mention with table name as:
SELECT TableName.from FROM TableName
While you are doing it - alias it as something else (or better yet, use a view or an SP and deprecate the old direct access method).
SELECT [from] AS TransferFrom -- Or something else more suitable
FROM TableName
Your question seems to be well answered here, but I just want to add one more comment to this subject.
Those designing the database should be well aware of the reserved keywords and avoid using them. If you discover someone using it, inform them about it (in a polite way). The keyword here is reserved word.
More information:
"Reserved keywords should not be used
as object names. Databases upgraded
from earlier versions of SQL Server
may contain identifiers that include
words not reserved in the earlier
version, but that are reserved words
for the current version of SQL Server.
You can refer to the object by using
delimited identifiers until the name
can be changed."
http://msdn.microsoft.com/en-us/library/ms176027.aspx
and
"If your database does contain names
that match reserved keywords, you must
use delimited identifiers when you
refer to those objects. For more
information, see Identifiers (DMX)."
http://msdn.microsoft.com/en-us/library/ms132178.aspx
In Apache Drill, use backquotes:
select `from` from table;
If you ARE using SQL Server, you can just simply wrap the square brackets around the column or table name.
select [select]
from [table]
I have also faced this issue.
And the solution for this is to put [Column_Name] like this in the query.
string query= "Select [Name],[Email] from Person";
So it will work perfectly well.
Hi I work on Teradata systems that is completely ANSI compliant. Use double quotes " " to name such columns.
E.g. type is a SQL reserved keyword, and when used within quotes, type is treated as a user specified name.
See below code example:
CREATE TABLE alpha1
AS
(
SEL
product1
type_of_product AS "type"
FROM beta1
) WITH DATA
PRIMARY INDEX (product1)
--type is a SQL reserved keyword
TYPE
--see? now to retrieve the column you would use:
SEL "type" FROM alpha1
I ran in the same issue when trying to update a column which name was a keyword. The solution above didn't help me. I solved it out by simply specifying the name of the table like this:
UPDATE `survey`
SET survey.values='yes,no'
WHERE (question='Did you agree?')
The following will work perfectly:
SELECT DISTINCT table.from AS a FROM table
Some solid answers—but the most-upvoted one is parochial, only dealing with SQL Server. In summary:
If you have source control, the best solution is to stick to the rules, and avoid using reserved words. This list has been around for ages, and covers most of the peculiarities. One tip is that reserved words are rarely plural—so you're usually safe using plural names. Exceptions are DIAGNOSTICS, SCHEMAS, OCTETS, OFFSETS, OPTIONS, VALUES, PARAMETERS, PRIVILEGES and also verb-like words that also appear plural: OVERLAPS, READS, RETURNS, TRANSFORMS.
Many of us don't have the luxury of changing the field names. There, you'll need to know the details of the RDBM you're accessing:
For SQL Server use [square_braces] around the name. This works in an ODBC connection too.
For MySQL use `back_ticks`.
Postgres, Oracle and several other RDBMs will apparently allow "double_quotes" to be used.
Dotting the offending word onto the table name may also work.
You can put your column name in bracket like:
Select [from] from < ur_tablename>
Or
Put in a temprary table then use as you like.
Example:
Declare #temp_table table(temp_from varchar(max))
Insert into #temp_table
Select * from your_tablename
Here I just assume that your_tablename contains only one column (i.e. from).
In MySQL, alternatively to using back quotes (`), you can use the UI to alter column names. Right click the table > Alter table > Edit the column name that contains sql keyword > Commit.
select [from] from <table>
As a note, the above does not work in MySQL
Judging from the answers here and my own experience. The only acceptable answer, if you're planning on being portable is don't use SQL keywords for table, column, or other names.
All these answers work in the various databases but apparently a lot don't support the ANSI solution.
Simple solution
Lets say the column name is from ; So the column name in query can be referred by table alias
Select * from user u where u.from="US"
In Oracle SQL Developer, pl/sql you can do this with double quotes but if you use double quotes you must type the column names in upper case. For example, SELECT "FROM" FROM MY_TABLE
I'm new to Oracle SQL. I came across the following statement:
CREATE TABLE &&DATABASE_ONE..TABLE_ONE(...);
The statement above is trying to create a table. I'm not sure if I have correct understanding on .. and &&.
I have done some Googling, I found out this link that says double dot(..) will choose the default schema for the query.
DATABASE_ONE should be the schema name, and TABLE_ONE should be the table name.
I'm confused of using && in front of the database name. After Googling, I found out some posts say that && means "Oracle will prompt the user for a value and will create a permanent variable".
Could someone explain how && works in the statement above? Please correct me if I have any misunderstanding.
#Gary_W has covered the difference between a single and a double ampersand.
The double period is perhaps slightly less obvious. From the SQL*Plus documentation:
If you wish to append characters immediately after a substitution variable, use a period to separate the variable from the character.
If you had a single period:
&&DATABASE_ONE.TABLE_ONE
then that period would be treated as the terminator for the substituion variable name, and would be consumed in the process. Say the value you entered was 'HR'; the substitution would be:
old:select &&DATABASE_ONE.TABLE_ONE from dual
new:select HRTABLE_ONE from dual
select HRTABLE_ONE from dual
As you can see, there is now no period between the schema and table names, giving you a combined identifier which will not represent what you intended.
With the form you have:
&&DATABASE_ONE..TABLE_ONE
the second period is the 'normal' one that sits between those two elements; once the first has been consumed by the substitution, the second remains to fulfil that function:
old:select &&DATABASE_ONE..TABLE_ONE from dual
new:select HR.TABLE_ONE from dual
select HR.TABLE_ONE from dual
The double ampersand will prompt once and everywhere that variable is used it will use what was entered. If it had only one ampersand, you would get a prompt for every occurrence.
Try it yourself by creating a dummy script with multiple prompts for the same variable. First use single ampersands, note how it works then switch to double ampersands.
This link has a good explanation: https://www.oreilly.com/library/view/oracle-sqlplus-the/1565925785/ch04s02.html
This is very simple but somehow I'm doing something wrong with this query on my database.
I have this query below:
SELECT login FROM accounts WHERE login = "loginname";
When I execute this query the result I get is this:
column "loginname" does not exist
This is a no brainer, why is this query not working properly? I have a login column and I know that this user exists because I've found this person with the rails console. Why is the login criteria referring to itself as a column?
Try with single quotes '' if you are trying to match a string
SELECT login FROM accounts WHERE login = 'loginname';
Check the documentation
There is a second kind of identifier: the delimited identifier or
quoted identifier. It is formed by enclosing an arbitrary sequence of
characters in double-quotes ("). A delimited identifier is always an
identifier, never a key word. So "select" could be used to refer to a
column or table named "select", whereas an unquoted select would be
taken as a key word and would therefore provoke a parse error when
used where a table or column name is expected.
Double quotes (") are used to refer to object names, in a case sensitive way. In this case, "loginname" is interpreted as a column name, and the query fails, since there is no such column. In order to refer to a string literal, you should use single quotes ('):
SELECT login FROM accounts WHERE login = 'loginname';
-- Here ---------------------------------^---------^
It seems that the " " are the problem if you believe the documentation. Single quotes are required for string values.
From the PostgreSQL Documentation:
There is a second kind of identifier: the delimited identifier or quoted identifier. It is formed by enclosing an arbitrary sequence of characters in double-quotes ("). A delimited identifier is always an identifier, never a key word. So "select" could be used to refer to a column or table named "select", whereas an unquoted select would be taken as a key word and would therefore provoke a parse error when used where a table or column name is expected. The example can be written with quoted identifiers like this:
UPDATE "my_table" SET "a" = 5;
Quoted identifiers can contain any character, except the character with code zero. (To include a double quote, write two double quotes.) This allows constructing table or column names that would otherwise not be possible, such as ones containing spaces or ampersands. The length limitation still applies.
So in your query "loginname" is the same as having loginname without quotes - it's attempting to refer to a column with that name. To make it a literal string, use single-quotes instead.
In ActiveRecord (using Ruby on Rails), if i have #products variable where #products = Product.all, and I say:
#products.where("name = 'check123' "), it returns an array of objects matching that condition, if i however go #products.where('name="check123"') i get an error?
: SELECT "products".* FROM "products" WHERE (name = "check123")
Hirb Error: PG::UndefinedColumn: ERROR: column "check123" does not exist
LINE 1: SELECT "products".* FROM "products" WHERE (name = "check123"...
^
Why is this happening? It seems that I must always use double quotes around everything in the where clause and single quotes for any strings inside there ?
Shouldn't single quotes work here as well, or is there something Im not getting
Some other observations:
#products.where("cost = '23.0'") works, event though 23 has a datatype of integer and not string?
#products.where('cost = 23') works, so I know i can use single quotes inside the where clause
NOTE: I am aware of using the '?' syntax inside the where clause to avoid sql injections, I am purposefully trying to execute the query like this.
Double quotes are used for naming database objects (table names, columns names, user names, schema names...) whilst single quotes are intended to represent strings to be used as values.
so your UndefinedColumn: ERROR makes sense as when filtering with #products.where('name="check123"') the SQL produced will be .... where name = "check123". The db engine is trying to find a column with the name check123 and match its value to the value of column name. As the column check123 does not exist in your table, you get an "undefined column name" error.
For your other question:
When you filter an integer column by a string value what happens is that the db engine does an implicit conversion of the column values to string in order to perform the search.
Update
The general SQL standard is described by this question's answers. In summary most Db engines follow most of the ANSI standard, and the use of double quotes is usually reserved for database objects.
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.