Improve SQL Query Performance by Using Bind Variables

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Compare the performance and security benefits of using bind variables, substitution variables, and literals in SQL statements. When you use SQL to communicate data between your web application and a database, you have the option to include the literal data in an SQL statement or use bind variables. Bind variables are placeholders for actual values in SQL statements. Writing SQL statements with bind bind sql example rather than substitution variables or literals minimizes processing time and bind sql example improve application performance by 20 to 30 percent.

Using bind variables can also help prevent an SQL injection attack. This article compares the performance and security benefits of using bind variables also known as bind parameters or dynamic parameters rather than substitution variables or literals in SQL statements.

I briefly introduce bind variables, then demonstrate how they're used in SQL statements and show the resulting performance improvement. I also show you how to use bind variables to effectively deter an SQL injection attack in a sample Java application. A bind variable consists of a variable indicated by a placeholder character such as bind sql example question mark? The placeholder character depends on the SQL database server that you use.

You provide the actual value of the placeholder at runtime, just before the SQL statement is executed. Each time an SQL statement is sent to a database, an exact text match is performed to see if the statement is already present in the shared pool. If no matching statement is found, the database performs a hard parse of that statement.

If a matching statement is found, then the database initiates a soft parse. Using bind variables enables soft parsing, which means that less processing time is spent on choosing an optimized execution plan. Information about how to process the SQL statement has been bind sql example, along with the SQL statement itself, in a shared pool.

Different APIs perform binding bind sql example one of two ways: Binding by value takes an actual value bind sql example each execution. Binding by reference uses the value found at a specific memory address. There are distinct performance advantages to using bind variables. For one, holding many similar but unique SQL statements in a shared pool is a waste of memory; writing one statement with interchangeable variables is more efficient.

It is also time-consuming to parse SQL statements. Reducing the number of hard parses minimizes CPU usage. Let's compare the respective performance impact of using literals, substitution variables, and bind variables. Literals are values directly passed to an SQL query. For instance, you could execute the two queries in Listing 1 with literals:. In this case, both queries were parsed separately, so there are two separate queries in the shared pool.

When a substitution variable is used in a statement, an input value is requested and rewrites the statement to include it. The rewritten statement is passed to the database. As a result, the database server knows nothing of the substitution variable. Listing 4 shows an example of substitution variables:. Once again, both statements were parsed separately, and there are two separate queries in the shared pool. As far as the database server is concerned, literals and substitution variables are the same.

Now I show how using bind variables affects the shared pool. Listing 7 follows the same format as the previous ones:. In this case, as you can see, the same SQL statement was executed twice, so that only one SQL query resides in the shared pool. Literals and substitution variables require hard parsing, which consumes more CPU cycles than the soft parsing required for bind variables. This statistic represents the total CPU time used for parsing hard or soft in tens bind sql example milliseconds.

The statements present in bind sql example shared pool are bind sql example displayed. Next, Listing 11 executes the procedure and checks the CPU usage:. The results show that milliseconds of CPU time were used for parsing during the session. Next, I run the same queries using bind variables.

Listing 13 shows the same statement from Listing 10 with the substitution of bind variables. The bind sql example show that milliseconds of CPU time were used on parsing during the session. That is less than two thirds the amount used in the previous example. Now let's check the shared pool. In Listing 15as expected, there is only a single statement in the shared pool. These examples clearly demonstrate that replacing literals with bind variables saves both memory usage and CPU cycles.

In these cases, performance was enhanced by approximately 30 percent. The advantage of using bind variables is due to the fact that bind sql example database does not need to rebuild its execution plan for every SQL statement. Bind variables work for SQL statements that are exactly the same, where the only difference is in the value.

When using bind variables, you do not include the actual values but instead insert placeholders into an SQL statement.

The statement does not change during execution; only the values change. Next, I show the use of bind variables in context, measuring the performance advantage of using bind variables for SQL statements in a sample Java program. Listing 16 represents a typical Java program where the SQL statements have been written using literals. A new SQL statement is created for every loop. Each time the loop encounters a new value, a new SQL query is created and executed. It took approximately 11 seconds to execute this code.

Now let's rewrite the code using prepared statements and bind variables. In Listing 17, a bind sql example is sent to the server with a bind variable defined. During execution, we bind the Java variable " i " to the SQL statement. We bind sql example thus able to use the same execution plan for 10, queries, which improves performance by minimizing SQL parsing.

This code took approximately seven seconds to execute. Note, however, that the code creates a new statement for each loop. We can improve on this result by creating just one statement and reusing it for each loop, as shown in Listing It took approximately 4 seconds for this Java code to perform the same SQL operation as the original code, which took 11 seconds. In an SQL injection attackmalicious SQL statements are inserted via an entry field into a web application's database, bind sql example order to force the application to execute them.

For an SQL injection attack to work, the application code must be vulnerable to user input. SQL injection attacks take advantage of an application's vulnerability to user input bind sql example is either incorrectly filtered for string literal escape characters with embedded SQL statements, or input that is not strongly typed.

The following section discusses the two types of security vulnerability that can promote an SQL injection attack. In the first type of attack, a hacker puts text that includes escape characters and embedded SQL bind sql example into a web application form field or query attribute. If the web application doesn't filter out the escape characters, the text, with the malicious SQL statements, is passed into the database for execution.

If empName is set from a web application's form field, the attacker could enter the following in the empName field:. If the bind sql example application code doesn't escape the single-quote ' character, it is included in the SQL statement as-is, resulting in the following new SQL statement:.

The attacker will successfully retrieve data about every employee in the database. Another common attack is to inject comments maliciously into an SQL statement, blocking the rest of the query from being executed. Three types of SQL comment can be injected, as shown here:.

Any of the previous three inputs maliciously injected into an SQL statement would block the remainder of the query. Attackers can also add malicious Bind sql example statements to the end of an existing statement. For example, the value of empName in the following statement would cause the emp table to be deleted. In an API that allowed multiple statements, the selection of all the data from the userinfo table would also be deleted.

This safeguard prevents attackers from injecting new queries, but it doesn't stop them from modifying existing ones. The second bind sql example of SQL injection attack occurs when user input isn't validated for its data type. For instance, a programmer might fail to validate user input for a numeric field, as shown here:. If successfully passed, this statement would cause the SQL database server to delete the users table from the database.

The resulting escaped strings treat the variable as user data and cannot be interpreted by the SQL database server as an SQL bind sql example.

Therefore, any bind sql example data must be escaped before it is added to an SQL statement. Any malicious SQL statements passed in through the userID variable is rendered as non-executable in the escaped version of the input. I conclude with a quick review of the syntax for bind variables in common database programming environments. Listing 22 shows an example:. In this article, I bind sql example bind variables and used code samples to demonstrate how they compare to substitution bind sql example and literals in terms of performance impact.

As you've seen, using bind variables in your SQL statements can improve performance measurements of SQL execution by up to 30 percent. Using bind variables is also a known defense against SQL injection attacks see Related topics. I demonstrated several types of SQL injection attack and showed you how to use bind variables in a number of common database programming environments. Sign in or register to add and subscribe to comments.

Using SQL bind variables for application performance and security Compare the performance and security benefits of using bind variables, substitution variables, and literals in SQL statements. Bipin Chandra Published on January 14, Bind sql example ways to bind Different APIs perform binding in one of two ways: Performance summary The advantage of using bind variables is due to the fact that a database does not need to rebuild its execution plan for every SQL statement.

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It is useful when writing general-purpose and flexible programs like ad hoc query systems, when writing programs that must run database definition language DDL statements, or when you do not know at compilation time the full text of a SQL statement or the number or data types of its input and output variables. However, to write native dynamic SQL code, you must know at compile time the number and data types of the input and output variables of the dynamic SQL statement.

Successful compilation verifies that static SQL statements reference valid database objects and that the necessary privileges are in place to access those objects. For more information about SQL cursor attributes, see "Cursors". Every bind variable that corresponds to a placeholder for a subprogram parameter has the same parameter mode as that subprogram parameter as in Example and a data type that is compatible with that of the subprogram parameter.

For information about compatible data types, see "Formal and Actual Subprogram Parameters". To work around this restriction, use an uninitialized variable where you want to use NULL , as in Example Use the FETCH statement to retrieve result set rows one at a time, several at a time, or all at once.

Example lists all employees who are managers, retrieving result set rows one at a time. If you repeat placeholder names in dynamic SQL statements, be aware that the way placeholders are associated with bind variables depends on the kind of dynamic SQL statement. For example, in this dynamic SQL statement, the repetition of the name: They can be different; for example:.

To associate the same bind variable with each occurrence of: If you repeat a placeholder name, you need not repeat its corresponding bind variable. In Example , all references to the first unique placeholder name,: SQL injection maliciously exploits applications that use client-supplied data in SQL statements, thereby gaining unauthorized access to a database to view or manipulate restricted data.

To try the examples in this topic, connect to the HR schema and run the statements in Example All SQL injection techniques exploit a single vulnerability: String input is not correctly validated and is concatenated into a dynamic SQL statement.

Statement modification means deliberately altering a dynamic SQL statement so that it runs in a way unintended by the application developer. Example creates a procedure that is vulnerable to statement modification and then invokes that procedure with and without statement modification. With statement modification, the procedure returns a supposedly secret record. Example Procedure Vulnerable to Statement Modification. Example creates a procedure that is vulnerable to statement injection and then invokes that procedure with and without statement injection.

With statement injection, the procedure deletes the supposedly secret record exposed in Example Example Procedure Vulnerable to Statement Injection. One datetime format model is " text ". The text is copied into the conversion result. The datetime format model can be abused as shown in Example You can use the following techniques:. The database uses the values of bind variables exclusively and does not interpret their contents in any way. Bind variables also improve performance.

The procedure in Example is invulnerable to SQL injection because it builds the dynamic SQL statement with bind variables not by concatenation as in the vulnerable procedure in Example The same binding technique fixes the vulnerable procedure shown in Example Always have your program validate user input to ensure that it is what is intended. For example, if the user is passing a department number for a DELETE statement, check the validity of this department number by selecting from the departments table.

This prevents a malicious user from injecting text between an opening quotation mark and its corresponding closing quotation mark. Ensure that the converted values have the format of SQL datetime or numeric literals.

Using explicit locale-independent format models to construct SQL is recommended not only from a security perspective, but also to ensure that the dynamic SQL statement runs correctly in any globalization environment. Successful compilation creates schema object dependencies. If the dynamic SQL statement invokes a subprogram, ensure that: Specify mode for first parameter. Modes of other parameters are correct by default.

They can be different; for example: The dynamic SQL statement retrieves rows into records. FOR i IN SQL Injection SQL injection maliciously exploits applications that use client-supplied data in SQL statements, thereby gaining unauthorized access to a database to view or manipulate restricted data.

Serve dinner at Cafe Pete Example of statement modification: You can use the following techniques: Validation Checks Always have your program validate user input to ensure that it is what is intended.

When checking the validity of a user name and its password, always return the same error regardless of which item is invalid. Otherwise, a malicious user who receives the error message "invalid password" but not "invalid user name" or the reverse can realize that he or she has guessed one of these correctly. Salaries were updated for: