Can I use placeholders in a prepared statement for the order by clause of my query?
I'm guessing not, as I tried it, and it didn't seem to work, but it didn't throw any errors either, which seemed strange.
Is there a better way to do this, other than just generating an SQL string with the validated inputs?
No, you can't use placeholders for column name. From DBI manual:
With most drivers, placeholders can't be used for any element of a statement that would prevent the database server from validating the statement and creating a query execution plan for it.
But still you can construct query in perl. In this case use quote_identifier method to quote column name.
Related
I'm relatively new to DB2 for IBMi and am wondering the methods of how to properly cleanse data for a dynamically generated query in PHP.
For example if writing a PHP class which handles all database interactions one would have to pass table names and such, some of which cannot be passed in using db2_bind_param(). Does db2_prepare() cleanse the structured query on its own? Or is it possible a malformed query can be "executed" within a db2_prepare() call? I know there is db2_execute() but the db is doing something in db2_prepare() and I'm not sure what (just syntax validation?).
I know if the passed values are in no way effected by the result of user input there shouldn't be much of an issue, but if one wanted to cleanse data before using it in a query (without using db2_prepare()/db2_execute()) what is the checklist for db2? The only thing I can find is to escape single quotes by prefixing them with another single quote. Is that really all there is to watch out for?
There is no magic "cleansing" happening when you call db2_prepare() -- it will simply attempt to compile the string you pass as a single SQL statement. If it is not a valid DB2 SQL statement, the error will be returned. Same with db2_exec(), only it will do in one call what db2_prepare() and db2_execute() do separately.
EDIT (to address further questions from the OP).
Execution of every SQL statement has three stages:
Compilation (or preparation), when the statement is parsed, syntactically and semantically analyzed, the user's privileges are determined, and the statement execution plan is created.
Parameter binding -- an optional step that is only necessary when the statement contains parameter markers. At this stage each parameter data type is verified to match what the statement text expects based on the preparation.
Execution proper, when the query plan generated at step 1 is performed by the database engine, optionally using the parameter (variable) values provided at step 2. The statement results, if any, are then returned to the client.
db2_prepare(), db2_bind_param(), and db2_execute() correspond to steps 1, 2 and 3 respectively. db2_exec() combines steps 1 and 3, skipping step 2 and assuming the absence of parameter markers.
Now, speaking about parameter safety, the binding step ensures that the supplied parameter values correspond to the expected data type constraints. For example, in the query containing something like ...WHERE MyIntCol = ?, if I attempt to bind a character value to that parameter it will generate an error.
If instead I were to use db2_exec() and compose a statement like so:
$stmt = "SELECT * FROM MyTab WHERE MyIntCol=" . $parm
I could easily pass something like "0 or 1=1" as the value of $parm, which would produce a perfectly valid SQL statement that only then will be successfully parsed, prepared and executed by db2_exec().
I primarily use CFQUERYPARAM to prevent SQL injection. Since Query-of-Queries (QoQ) does not touch the database, is there any logical reason to use CFQUERYPARAM in them? I know that values that do not match the cfsqltype and maxlength will throw an exception, but, these values should already be validated before that and display friendly messages (from a UX viewpoint).
Since Query-of-Queries (QoQ) does not touch the database, is there any logical reason to use CFQUERYPARAM in them? Actually, it does touch the database, the database that you currently have stored in memory. The data in that database could still theoretically be tampered with via some sort of injection from the user. Does that affect your physical database - no. Does that affect the use of the data within your application - yes.
You did not give any specific details but I would err on the side of caution. If ANY of the data you are using to build your query comes from the client then use cfqueryparam in them. If you can guarantee that none of the elements in your query comes from the client then I think it would be okay to not use the cfqueryparam.
As an aside, using cfqueryparam also helps optimize the query for the database although I'm not sure if that is true for query of queries. It also escapes characters for you like apostrophes.
Here is a situation where it's simpler, in my opinion.
<cfquery name="NoVisit" dbtype="query">
select chart_no, patient_name, treatment_date, pr, BillingCompareField
from BillingData
where BillingCompareField not in
(<cfqueryparam cfsqltype="cf_sql_varchar"
value="#ValueList(FinalData.FinalCompareField)#" list="yes">)
</cfquery>
The alternative would be to use QuotedValueList. However, if anything in that value list contained an apostrophe, cfqueryparam will escape it. Otherwise I would have to.
Edit starts here
Here is another example where not using query parameters causes an error.
QueryAddRow(x,2);
QuerySetCell(x,"dt",CreateDate(2001,1,1),1);
QuerySetCell(x,"dt",CreateDate(2001,1,11),2);
</cfscript>
<cfquery name="y" dbtype="query">
select * from x
<!---
where dt in (<cfqueryparam cfsqltype="cf_sql_date" value="#ValueList(x.dt)#" list="yes">)
--->
where dt in (#ValueList(x.dt)#)
</cfquery>
The code as written throws this error:
Query Of Queries runtime error.
Comparison exception while executing IN.
Unsupported Type Comparison Exception:
The IN operator does not support comparison between the following types:
Left hand side expression type = "DATE".
Right hand side expression type = "LONG".
With the query parameter, commented out above, the code executes successfully.
I was planning to use the WITH clause with PostgreSQL, but it doesn't seem to support the command. Is there a substitute command?
What I want to do is with one query select several sub-resultsets and use parts of the sub-resultsets to create my final SELECT.
That would have been easy using the WITH clause.
UPDATE:
Opps! I discovered that I misunderstood the error message I got; and pgSQL does support WITH.
PostgreSQL supports common-table expressions (WITH queries) in version 8.4 and above. See common table expressions in the manual.
You should really include your PostgreSQL version, the exact text of the error message, and the exact text of any query you ran in your question. Where practical/relevant also include table definitions, sample data, and expected results.
NOTE: It's probably a duplicate but I can't find working answer.
Following is what i'm trying todo, notice a ' in the value. How do I fix this?
INSERT INTO [pugraider].[dbo].[Realms]([Name]) VALUES('Aman'Thul')
I use MS SQL Server Management Studio 2008.
EDIT: I'm writing a script to populate a lookup table (ID<->Name).
This will work:-
INSERT INTO [pugraider].[dbo].[Realms]([Name]) VALUES('Aman''Thul')
Ordinarily the only reason to have such hardcoded values in T-SQL is in DB construction code such as initialising look up tables.
Otherwise this code might be a result of string concatenation to build up some T-SQL from some input source. If that is the case its worth finding ways to avoid it since it can open your application to SQL injection attacks.
I have some code which utilizes parameterized queries to prevent against injection, but I also need to be able to dynamically construct the query regardless of the structure of the table. What is the proper way to do this?
Here's an example, say I have a table with columns Name, Address, Telephone. I have a web page where I run Show Columns and populate a select drop-down with them as options.
Next, I have a textbox called Search. This textbox is used as the parameter.
Currently my code looks something like this:
result = pquery('SELECT * FROM contacts WHERE `' + escape(column) + '`=?', search);
I get an icky feeling from it though. The reason I'm using parameterized queries is to avoid using escape. Also, escape is likely not designed for escaping column names.
How can I make sure this works the way I intend?
Edit:
The reason I require dynamic queries is that the schema is user-configurable, and I will not be around to fix anything hard-coded.
Instead of passing the column names, just pass an identifier that you code will translate to a column name using a hardcoded table. This means you don't need to worry about malicious data being passed, since all the data is either translated legally, or is known to be invalid. Psudoish code:
#columns = qw/Name Address Telephone/;
if ($columns[$param]) {
$query = "select * from contacts where $columns[$param] = ?";
} else {
die "Invalid column!";
}
run_sql($query, $search);
The trick is to be confident in your escaping and validating routines. I use my own SQL escape function that is overloaded for literals of different types. Nowhere do I insert expressions (as opposed to quoted literal values) directly from user input.
Still, it can be done, I recommend a separate — and strict — function for validating the column name. Allow it to accept only a single identifier, something like
/^\w[\w\d_]*$/
You'll have to rely on assumptions you can make about your own column names.
I use ADO.NET and the use of SQL Commands and SQLParameters to those commands which take care of the Escape problem. So if you are in a Microsoft-tool environment as well, I can say that I use this very sucesfully to build dynamic SQL and yet protect my parameters
best of luck
Make the column based on the results of another query to a table that enumerates the possible schema values. In that second query you can hardcode the select to the column name that is used to define the schema. if no rows are returned then the entered column is invalid.
In standard SQL, you enclose delimited identifiers in double quotes. This means that:
SELECT * FROM "SomeTable" WHERE "SomeColumn" = ?
will select from a table called SomeTable with the shown capitalization (not a case-converted version of the name), and will apply a condition to a column called SomeColumn with the shown capitalization.
Of itself, that's not very helpful, but...if you can apply the escape() technique with double quotes to the names entered via your web form, then you can build up your query reasonably confidently.
Of course, you said you wanted to avoid using escape - and indeed you don't have to use it on the parameters where you provide the ? place-holders. But where you are putting user-provided data into the query, you need to protect yourself from malicious people.
Different DBMS have different ways of providing delimited identifiers. MS SQL Server, for instance, seems to use square brackets [SomeTable] instead of double quotes.
Column names in some databases can contain spaces, which mean you'd have to quote the column name, but if your database contains no such columns, just run the column name through a regular expression or some sort of check before splicing into the SQL:
if ( $column !~ /^\w+$/ ) {
die "Bad column name [$column]";
}