I have to store some strange characters in my SQL Server DB which are used by an Epson Receipt Printer code page.
Using an INSERT statement, all are stored correctly except one - [SCI] (nchar(154)). I realise that this is a control character that isn't representable in a string, but the character is replaced by a '?' in the stored DB string, suggesting that it is being parsed (unsuccessfully) somewhere.
The collation of the database is LATIN1_GENERAL_CI_AS so it should be able to cope with it.
So, for example, if I run this INSERT:
INSERT INTO Table(col1) VALUES ('abc[SCI]123')
Where [SCI] is the character, a resulting SELECT query will return 'abc?123'.
However, if I use NCHAR(154), by directly inserting or by using a REPLACE command such as:
UPDATE Table SET col1 = REPLACE(col1, '?', NCHAR(154))
The character is stored correctly.
My question is, why? And how can I store it directly from an INSERT statement? The latter is preferable as I am writing from an existing application that produces the INSERT statement that I don't really want to have to change.
Thank you in advance for any information that may be useful.
When you write a literal string in SQL is is created as a VARCHAR unless you prefix is with N. This means if you include any Unicode characters, they will be removed. Instead write your INSERT statement like this:
INSERT INTO Table(col1) VALUES (N'abc[SCI]123')
I'm so confused or rather I'm like, soooooooooo confused with pdo prepared statements. I know that prepared statements are the best way to keep data safe from hackers.
From : How can prepared statements protect from SQL injection attacks?
We are sending program to the server first
$db->prepare("SELECT * FROM users where id=?"); where the data is
substituted by some variable called "placeholder".
Note that the very same query being sent to the server, without any
data in it! And then we're sending the data with the second request,
totally separated from the query itself:
$db->execute($data);
query-
$query=$db->prepare("SELECT * FROM USERS WHERE username=?");
$query->execute(array($tex));
$tex=blah; DROP TABLE users;--
then it will be like - SELECT * FROM USERS WHERE username=blah; DROP TABLE users;--
how prepare statements will help me with this example above?
I'm really sorry if this question is vague to understand. Any help would be appreciated. Thanks in advance.
The prepared statement handler will make sure the bound value is always used as valid SQL value/literal (ie. an SQL string or a number) and never as 'raw SQL text'1.
This is why placeholders values cannot be used as identifiers such as column or table names or act as other SQL keywords; and cannot generate the vulnerable query hypothesized. Instead it is treated as the following:
WHERE username='blah; DROP TABLE users;--'
--^ placeholder ensures valid SQL string value is used
-- (note automatic/implicit addition of SQL quotes)
And even when binding with 'more tricky' data:
$tex = "blah'; DROP TABLE users;--"; // embedded SQL quote character
It would still be safe:
WHERE username='blah''; DROP TABLE users;--'
--^ placeholder STILL ensures valid SQL string value is used
Thus, when using placeholders, it is impossible to generate the SQL that is vulnerable (in this way).
For SQL Injection the 'shape' of the query (which includes keywords and identifiers, but excludes values) must itself be altered by the input.
1 Technically placeholders values can also be sent through a separate data channel (depending on adapter/driver) and thus might not even appear in the raw SQL query itself.
However a simple way to think about why placeholders are safe, or how they 'work' is:
When using placeholders the adapter ensures that the equivalent of 'sql really safe escape' and applicable quoting is always used for every bound text value - and is thus impossible for accidentally forget.
I have a table test(id,name).
I need to insert values like: user's log, 'my user', customer's.
insert into test values (1,'user's log');
insert into test values (2,''my users'');
insert into test values (3,'customer's');
I am getting an error if I run any of the above statements.
If there is any method to do this correctly please share. I don't want any prepared statements.
Is it possible using sql escaping mechanism?
String literals
Escaping single quotes ' by doubling them up → '' is the standard way and works of course:
'user's log' -- incorrect syntax (unbalanced quote)
'user''s log'
Plain single quotes (ASCII / UTF-8 code 39), mind you, not backticks `, which have no special purpose in Postgres (unlike certain other RDBMS) and not double-quotes ", used for identifiers.
In old versions or if you still run with standard_conforming_strings = off or, generally, if you prepend your string with E to declare Posix escape string syntax, you can also escape with the backslash \:
E'user\'s log'
Backslash itself is escaped with another backslash. But that's generally not preferable.
If you have to deal with many single quotes or multiple layers of escaping, you can avoid quoting hell in PostgreSQL with dollar-quoted strings:
'escape '' with '''''
$$escape ' with ''$$
To further avoid confusion among dollar-quotes, add a unique token to each pair:
$token$escape ' with ''$token$
Which can be nested any number of levels:
$token2$Inner string: $token1$escape ' with ''$token1$ is nested$token2$
Pay attention if the $ character should have special meaning in your client software. You may have to escape it in addition. This is not the case with standard PostgreSQL clients like psql or pgAdmin.
That is all very useful for writing PL/pgSQL functions or ad-hoc SQL commands. It cannot alleviate the need to use prepared statements or some other method to safeguard against SQL injection in your application when user input is possible, though. #Craig's answer has more on that. More details:
SQL injection in Postgres functions vs prepared queries
Values inside Postgres
When dealing with values inside the database, there are a couple of useful functions to quote strings properly:
quote_literal() or quote_nullable() - the latter outputs the unquoted string NULL for null input.
There is also quote_ident() to double-quote strings where needed to get valid SQL identifiers.
format() with the format specifier %L is equivalent to quote_nullable().
Like: format('%L', string_var)
concat() or concat_ws() are typically no good for this purpose as those do not escape nested single quotes and backslashes.
According to PostgreSQL documentation (4.1.2.1. String Constants):
To include a single-quote character within a string constant, write
two adjacent single quotes, e.g. 'Dianne''s horse'.
See also the standard_conforming_strings parameter, which controls whether escaping with backslashes works.
This is so many worlds of bad, because your question implies that you probably have gaping SQL injection holes in your application.
You should be using parameterized statements. For Java, use PreparedStatement with placeholders. You say you don't want to use parameterised statements, but you don't explain why, and frankly it has to be a very good reason not to use them because they're the simplest, safest way to fix the problem you are trying to solve.
See Preventing SQL Injection in Java. Don't be Bobby's next victim.
There is no public function in PgJDBC for string quoting and escaping. That's partly because it might make it seem like a good idea.
There are built-in quoting functions quote_literal and quote_ident in PostgreSQL, but they are for PL/PgSQL functions that use EXECUTE. These days quote_literal is mostly obsoleted by EXECUTE ... USING, which is the parameterised version, because it's safer and easier. You cannot use them for the purpose you explain here, because they're server-side functions.
Imagine what happens if you get the value ');DROP SCHEMA public;-- from a malicious user. You'd produce:
insert into test values (1,'');DROP SCHEMA public;--');
which breaks down to two statements and a comment that gets ignored:
insert into test values (1,'');
DROP SCHEMA public;
--');
Whoops, there goes your database.
In postgresql if you want to insert values with ' in it then for this you have to give extra '
insert into test values (1,'user''s log');
insert into test values (2,'''my users''');
insert into test values (3,'customer''s');
you can use the postrgesql chr(int) function:
insert into test values (2,'|| chr(39)||'my users'||chr(39)||');
When I used Python to insert values into PostgreSQL, I also met the question: column "xxx" does not exist.
The I find the reason in wiki.postgresql:
PostgreSQL uses only single quotes for this (i.e. WHERE name = 'John'). Double quotes are used to quote system identifiers; field names, table names, etc. (i.e. WHERE "last name" = 'Smith').
MySQL uses ` (accent mark or backtick) to quote system identifiers, which is decidedly non-standard.
It means PostgreSQL can use only single quote for field names, table names, etc. So you can not use single quote in value.
My situation is: I want to insert values "the difference of it’s adj for sb and it's adj of sb" into PostgreSQL.
How I figure out this problem:
I replace ' with ’, and I replace " with '. Because PostgreSQL value does not support double quote.
So I think you can use following codes to insert values:
insert into test values (1,'user’s log');
insert into test values (2,'my users');
insert into test values (3,'customer’s');
If you need to get the work done inside Pg:
to_json(value)
https://www.postgresql.org/docs/9.3/static/functions-json.html#FUNCTIONS-JSON-TABLE
You must have to add an extra single quotes -> ' and make doubling quote them up like below examples -> ' ' is the standard way and works of course:
Wrong way: 'user's log'
Right way: 'user''s log'
problem:
insert into test values (1,'user's log');
insert into test values (2,''my users'');
insert into test values (3,'customer's');
Solutions:
insert into test values (1,'user''s log');
insert into test values (2,'''my users''');
insert into test values (3,'customer''s');
All B2A users.
Again about double quotes in SQL: how to be (replace quotes) in B2A long SQL INSERT\UPDATE request string, if this string is created dinamically, fields names and qty are variables (download by HTTP), and any value of them can be a string with quotes ?
Fields values are also in double quotes for INSERT, and I mean that whole the big SQL string cannot be easy formatted as string with & QUOTE & parts.
B4A gives SQLite exception "sintax error". Quotes in the values must be saved\used.... :-( not to be replaced by two single quotes.
What more symbols in the fields values must be specially checked (excepting destructive SQL injections...)?
The solution is to use parameterized queries with ExecQuery2 or ExecNonQuery2. SQL docs.
You can also use DBUtils.
I am trying to write an sql query and I am having a problem. When we want to write a query with a where clause to narrow down our results, we can do
... where name = 'John'
(Where name is a column in the table).
Now I am trying to insert a clause like this except the name is "O'Malley". So I thought the query would be
... where name = 'O'Malley'
but this gives me a null pointer exception.
Does anyone know how you could solve this problem?
Thanks for your help in advance.
Your problem is that the single quote in the string "O'Malley" is interpreted by SQL as the string terminator. To escape a single quote, replace it with two single quotes, like this:
where name = 'O''Malley'
Edit: If the string "O'Malley" came from a user input, your code is vulnerable to an SQL injection exploit. To avoid this risk, use a parameterized query.
Use bind variables to avoid thinking about quotation problems.
Bind variables beware of sql injection to.
Depending on the database you could escape the ' I think. Have a look at http://dev.mysql.com/doc/refman/5.0/en/string-syntax.html
If you use two apostrophes together in you search string SQL will realise that it is part of the string and isn't part of the SQL syntax.
where name = 'O''Malley'