How to dynamically assemble SQL statements in Oracle stored procedures

In Oracle database, a stored procedure is an executable program stored in the database that allows users to define their own functions, procedures and packages and process data. Stored procedures are usually used to handle complex business logic, but sometimes it is also necessary to dynamically assemble SQL statements in stored procedures.

In some cases, different SQL statements need to be assembled according to different parameters to be able to handle different query requirements. At this time, it is usually necessary to use dynamic SQL statements and dynamically construct SQL statements as needed in the stored procedure.

The following is an example of how to dynamically assemble SQL statements in Oracle stored procedures.

Example:

Suppose there is a table user table, which contains four fields: id, name, gender, and age, and you want to implement a stored procedure to query based on id and name, and Sort according to gender and age.

Step one: Declare the stored procedure

First, you need to declare the stored procedure and pass in the parameters. In this example, you need to pass in two parameters, id and name, in order to query based on these two parameters. The code is as follows:

CREATE OR REPLACE PROCEDURE get_user_list(
p_id IN NUMBER,
p_name IN VARCHAR2
)
IS
BEGIN
-- TODO: here Splicing SQL statements
END;

Second step: Dynamically splicing SQL statements

In the stored procedure, SQL statements need to be dynamically spliced ​​to query different data as needed. Since Oracle supports dynamic SQL, SQL statements can be constructed by splicing strings. The following is the code for dynamically splicing SQL statements:

CREATE OR REPLACE PROCEDURE get_user_list(
p_id IN NUMBER,
p_name IN VARCHAR2
)
IS
sql_stmt VARCHAR2(1000) ;
BEGIN
sql_stmt := 'SELECT * FROM users WHERE 1 = 1';

IF p_id IS NOT NULL THEN

sql_stmt := sql_stmt || ' AND id = ' || p_id;

END IF;

IF p_name IS NOT NULL THEN

sql_stmt := sql_stmt || ' AND name = ''' || p_name || '''';

END IF;

sql_stmt := sql_stmt || ' ORDER BY gender, age';

EXECUTE IMMEDIATE sql_stmt;
END ;

In the above code, a variable sql_stmt is first defined to save dynamically spliced ​​SQL statements. Then, splice the SQL statement as needed, and if the parameters are not empty, add the parameters to the SQL.

At the end, the SQL statement adds an ORDER BY clause to sort based on gender and age. Finally, use the EXECUTE IMMEDIATE statement to execute the SQL statement.

Summary

Through the above examples, you can see that in Oracle database, stored procedures can use dynamic SQL to splice SQL statements. This makes the stored procedure more flexible and can respond to different query requirements. However, when using dynamic SQL, you need to be aware of the risk of SQL injection. To prevent SQL injection, bind variables should be used instead of string concatenation.

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