oracle stored procedure returns result set

Oracle is one of the most famous relational database management systems in the world. Stored procedures are one of the important features, which allow us to encapsulate a set of SQL statements into a code block and return one or more result sets. However, returning a result set from a stored procedure in Oracle is not an easy task. In this article, we will introduce how to write a stored procedure and return a result set.

1. Basic introduction to stored procedures

A stored procedure is a database object similar to a function. It is written by a set of SQL statements, including the processing of one or more input parameters and the processing of returned results. Stored procedures can receive input parameters, perform specific calculations, queries, or operations, and return output parameters or a result set. Stored procedures can be used to complete database operations such as query, update, delete, insert, etc.

The advantage of stored procedures is their flexibility and reusability. Stored procedures can support parameterized input, and complex SQL statements can be written using logical control structures. It can also be called multiple times by multiple client applications and can be accessed and executed by different users and roles.

2. Methods for stored procedures to return result sets

Stored procedures can return single or multiple result sets, depending on the needs of the stored procedure. Here we introduce two methods to implement stored procedures to return result sets.

1. Using SYS_REFCURSOR

SYS_REFCURSOR is a data type provided by Oracle to reference the result set. By using SYS_REFCURSOR, a stored procedure can return a result set, and client applications can access and process the result set.

The following is an example of using SYS_REFCURSOR to return a result set:

CREATE OR REPLACE PROCEDURE sample_proc(
    p_param_1 IN VARCHAR2,
    p_param_2 IN OUT NUMBER,
    p_out_cur OUT SYS_REFCURSOR
)
IS
BEGIN
    OPEN p_out_cur FOR
    SELECT col_1, col_2, col_3
    FROM table_name
    WHERE column_name = p_param_1;

    p_param_2 := p_param_2 * 10;
END;

In this stored procedure, p_param_1 and p_param_2 are input parameters, and p_out_cur is the output parameter. The stored procedure will query data with p_param_1 as the condition, and store the query results in the parameter p_out_cur of type SYS_REFCURSOR.

2. Using Cursors

Another method is to use a cursor. A cursor is a mechanism for processing a result set row by row. When a stored procedure uses a cursor to return a result set, it can iterate over the result set row by row and return each row of data to the client application.

The following is an example of using a cursor to return a result set:

CREATE OR REPLACE PROCEDURE sample_proc(
    p_param_1 IN VARCHAR2,
    p_param_2 IN OUT NUMBER
)
IS
    c_cursor SYS_REFCURSOR;
    v_col_1 table_name.col_1%TYPE;
    v_col_2 table_name.col_2%TYPE;
    v_col_3 table_name.col_3%TYPE;
BEGIN
    OPEN c_cursor FOR
    SELECT col_1, col_2, col_3
    FROM table_name
    WHERE column_name = p_param_1;

    LOOP
        FETCH c_cursor INTO v_col_1, v_col_2, v_col_3;
        EXIT WHEN c_cursor%NOTFOUND;

        -- 处理逐行返回的数据
    END LOOP;

    p_param_2 := p_param_2 * 10;

    CLOSE c_cursor;
END;

In this stored procedure, p_param_1 and p_param_2 are input parameters. The stored procedure will query the data using p_param_1 as the condition and use the cursor to iterate over each row of data. For each row of data, the stored procedure can use variables to store the column data of the result set. The stored procedure can then use the CLOSE statement to close the cursor at the end.

3. Conclusion

Stored procedure is one of the important functions in Oracle. It allows us to encapsulate a set of SQL statements into a code block and return one or more result sets. In actual use, you can choose to use SYS_REFCURSOR or a cursor to return the result set as needed. Either approach requires writing some additional code. Therefore, before writing a stored procedure, make sure you are familiar with the relevant Oracle documentation and functions and can use them correctly to complete your requirements.

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