Bind sql example
That is pretty dramatic. How do these use bind variables? Do you have to in fact split your SQL into two statements, one to set the bind variable, and one for the statement itself? In fact, the answer to this is actually quite simple. All of these APIs have built-in support for bind variables , and it's just a case of using this support rather than just concatenating a string yourself and submitting it to the database.
For example, Java has PreparedStatement , which allows the use of bind variables, and Statement, which uses the string concatenation approach. If you use the method that supports bind variables, the API itself passes the bind variable value to Oracle at runtime, and you just submit your SQL statement as normal. There's no need to separately pass the bind variable value to Oracle, and actually no additional work on your part.
Lastly, it's worth bearing in mind that there are some instances where bind variables are probably not appropriate, usually where instead of your query being executed many times a second as with OLTP systems your query in fact actually takes several seconds, or minutes, or hours to execute - a situation you get in decision support and data warehousing.
In this instance, the time taken to hard parse your query is only a small proportion of the total query execution time, and the benefit of avoiding a hard parse is probably outweighed by the reduction in important information you're making available to the query optimizer - by substituting the actual predicate with a bind variable, you're removing the ability for the optimiser to compare your value with the data distribution in the column, which might make it opt for a full table scan or an index when this isn't appropriate.
Oracle 9i helps deal with this using a feature known as bind variable peeking , which allows Oracle to look at the value behind a bind variable to help choose the best execution plan. Another potential drawback with bind variables and data warehousing queries is that the use of bind variables disallows the potential for star transformations , taking away this powerful option for efficiently joining fact and dimension tables in a star schema. Bind variables - The key to application performance.
The Performance Killer Just to give you a tiny idea of how huge of a difference this can make performance wise, you only need to run a very small test: Here is the Performance Killer 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 of milliseconds. The statements present in the shared pool are also 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 results 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 15 , as 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 a 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 query is sent to the server with a bind variable defined. During execution, we bind the Java variable " i " to the SQL statement.
We are 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 attack , malicious SQL statements are inserted via an entry field into a web application's database, in 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 that 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 statements 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 web 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 SQL 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.