8
Coding Dynamic SQL Statements

Dynamic SQL is a programming technique that enables you to build SQL statements dynamically at runtime. You can create more general purpose, flexible applications by using dynamic SQL because the full text of a SQL statement may be unknown at compilation. For example, dynamic SQL lets you create a procedure that operates on a table whose name is not known until runtime.

Oracle includes two ways to implement dynamic SQL in a PL/SQL application:

• Native dynamic SQL, where you place dynamic SQL statements directly into PL/SQL blocks.
• Calling procedures in the DBMS_SQL package.

This chapter covers the following topics:

• "What Is Dynamic SQL?"
• "Why Use Dynamic SQL?"
• "A Dynamic SQL Scenario Using Native Dynamic SQL"
• "Choosing Between Native Dynamic SQL and the DBMS_SQL Package"
• "Using Dynamic SQL in Languages Other Than PL/SQL"
• "Using PL/SQL Records in SQL INSERT and UPDATE Statements"

You can find details about the DBMS_SQL package in the Oracle9i Supplied PL/SQL Packages and Types Reference.

What Is Dynamic SQL?

Dynamic SQL enables you to write programs that reference SQL statements whose full text is not known until runtime. Before discussing dynamic SQL in detail, a clear definition of static SQL may provide a good starting point for understanding dynamic SQL. Static SQL statements do not change from execution to execution. The full text of static SQL statements are known at compilation, which provides the following benefits:

• Successful compilation verifies that the SQL statements reference valid database objects.
• Successful compilation verifies that the necessary privileges are in place to access the database objects.
• Performance of static SQL is generally better than dynamic SQL.

Because of these advantages, you should use dynamic SQL only if you cannot use static SQL to accomplish your goals, or if using static SQL is cumbersome compared to dynamic SQL. However, static SQL has limitations that can be overcome with dynamic SQL. You may not always know the full text of the SQL statements that must be executed in a PL/SQL procedure. Your program may accept user input that defines the SQL statements to execute, or your program may need to complete some processing work to determine the correct course of action. In such cases, you should use dynamic SQL.

For example, a reporting application in a data warehouse environment might not know the exact table name until runtime. These tables might be named according to the starting month and year of the quarter, for example INV_01_1997, INV_04_1997, INV_07_1997, INV_10_1997, INV_01_1998, and so on. You can use dynamic SQL in your reporting application to specify the table name at runtime.

You might also want to run a complex query with a user-selectable sort order. Instead of coding the query twice, with different ORDER BY clauses, you can construct the query dynamically to include a specified ORDER BY clause.

Dynamic SQL programs can handle changes in data definitions, without the need to recompile. This makes dynamic SQL much more flexible than static SQL. Dynamic SQL lets you write reusable code because the SQL can be easily adapted for different environments..

Dynamic SQL also lets you execute data definition language (DDL) statements and other SQL statements that are not supported in purely static SQL programs.

Why Use Dynamic SQL?

You should use dynamic SQL in cases where static SQL does not support the operation you want to perform, or in cases where you do not know the exact SQL statements that must be executed by a PL/SQL procedure. These SQL statements may depend on user input, or they may depend on processing work done by the program. The following sections describe typical situations where you should use dynamic SQL and typical problems that can be solved by using dynamic SQL

Executing DDL and SCL Statements in PL/SQL

In PL/SQL, you can only execute the following types of statements using dynamic SQL, rather than static SQL:

• Data definition language (DDL) statements, such as CREATE, DROP, GRANT, and REVOKE
• Session control language (SCL) statements, such as ALTER SESSION and SET ROLE

  See Also: Oracle9i SQL Reference for information about DDL and SCL statements.

Also, you can only use the TABLE clause in the SELECT statement through dynamic SQL. For example, the following PL/SQL block contains a SELECT statement that uses the TABLE clause and native dynamic SQL:

CREATE TYPE t_emp AS OBJECT (id NUMBER, name VARCHAR2(20))
/
CREATE TYPE t_emplist AS TABLE OF t_emp
/

CREATE TABLE dept_new (id NUMBER, emps t_emplist)
    NESTED TABLE emps STORE AS emp_table;

INSERT INTO dept_new VALUES (
    10, 
    t_emplist(
        t_emp(1, 'SCOTT'),
        t_emp(2, 'BRUCE')));

DECLARE
    deptid NUMBER;
    ename  VARCHAR2(20);
BEGIN
    EXECUTE IMMEDIATE 'SELECT d.id, e.name
        FROM dept_new d, TABLE(d.emps) e  -- not allowed in static SQL
                                          -- in PL/SQL
        WHERE e.id = 1'
        INTO deptid, ename;
END;
/

Executing Dynamic Queries

You can use dynamic SQL to create applications that execute dynamic queries, whose full text is not known until runtime. Many types of applications need to use dynamic queries, including:

• Applications that allow users to input or choose query search or sorting criteria at runtime
• Applications that allow users to input or choose optimizer hints at run time
• Applications that query a database where the data definitions of tables are constantly changing
• Applications that query a database where new tables are created often

For examples, see "Querying Using Dynamic SQL: Example", and see the query examples in "A Dynamic SQL Scenario Using Native Dynamic SQL".

Referencing Database Objects that Do Not Exist at Compilation

Many types of applications must interact with data that is generated periodically. For example, you might know the tables definitions at compile time, but not the names of the tables.

Dynamic SQL can solve this problem, because it lets you wait until runtime to specify the table names. For example, in the sample data warehouse application discussed in "What Is Dynamic SQL?", new tables are generated every quarter, and these tables always have the same definition. You might let a user specify the name of the table at runtime with a dynamic SQL query similar to the following:

CREATE OR REPLACE PROCEDURE query_invoice(
       month VARCHAR2, 
       year VARCHAR2) IS
    TYPE cur_typ IS REF CURSOR;
    c cur_typ;
    query_str VARCHAR2(200);
    inv_num NUMBER;
    inv_cust VARCHAR2(20);
    inv_amt NUMBER;
BEGIN
    query_str := 'SELECT num, cust, amt FROM inv_' || month ||'_'|| year 
      || ' WHERE invnum = :id';
    OPEN c FOR query_str USING inv_num;
    LOOP
        FETCH c INTO inv_num, inv_cust, inv_amt;
        EXIT WHEN c%NOTFOUND;
        -- process row here
    END LOOP;
    CLOSE c;
END;
/

Optimizing Execution Dynamically

You can use dynamic SQL to build a SQL statement in a way that optimizes the execution by concatenating the hints into a SQL statement dynamically. This lets you change the hints based on your current database statistics, without requiring recompilation.

For example, the following procedure uses a variable called a_hint to allow users to pass a hint option to the SELECT statement:

CREATE OR REPLACE PROCEDURE query_emp
      (a_hint VARCHAR2) AS
   TYPE cur_typ IS REF CURSOR;
   c cur_typ;
BEGIN
   OPEN c FOR 'SELECT ' || a_hint ||
      ' empno, ename, sal, job FROM emp WHERE empno = 7566';
      -- process
END;
/

In this example, the user can pass any of the following values for a_hint:

a_hint = '/*+ ALL_ROWS */'

a_hint = '/*+ FIRST_ROWS */'

a_hint = '/*+ CHOOSE */'

or any other valid hint option.

See Also: Oracle9i Database Performance Guide and Reference for more information about using hints.

Executing Dynamic PL/SQL Blocks

You can use the EXECUTE IMMEDIATE statement to execute anonymous PL/SQL blocks. You can add flexibility by constructing the block contents at runtime.

For example, suppose ythroughthroughou want to write an application that takes an event number and dispatches to a handler for the event. The name of the handler is in the form EVENT_HANDLER_event_num, where event_num is the number of the event. One approach is to implement the dispatcher as a switch statement, where the code handles each event by making a static call to its appropriate handler. This code is not very extensible because the dispatcher code must be updated whenever a handler for a new event is added.

CREATE OR REPLACE PROCEDURE event_handler_1(param number) AS BEGIN 
   -- process event
   RETURN; 
END;
/

CREATE OR REPLACE PROCEDURE event_handler_2(param number) AS BEGIN 
   -- process event
   RETURN; 
END;
/

CREATE OR REPLACE PROCEDURE event_handler_3(param number) AS BEGIN 
   -- process event
   RETURN; 
END;
/

CREATE OR REPLACE PROCEDURE event_dispatcher
   (event number, param number) IS
BEGIN
  IF (event = 1) THEN
    EVENT_HANDLER_1(param);
  ELSIF (event = 2) THEN
    EVENT_HANDLER_2(param);
  ELSIF (event = 3) THEN
    EVENT_HANDLER_3(param);
  END IF;
END;
/

Using native dynamic SQL, you can write a smaller, more flexible event dispatcher similar to the following:

CREATE OR REPLACE PROCEDURE event_dispatcher
   (event NUMBER, param NUMBER) IS
BEGIN
  EXECUTE IMMEDIATE
     'BEGIN
        EVENT_HANDLER_' || to_char(event) || '(:1);
     END;'
  USING param;
END;
/

Performing Dynamic Operations Using Invoker-Rights

By using the invoker-rights feature with dynamic SQL, you can build applications that issue dynamic SQL statements under the privileges and schema of the invoker. These two features, invoker-rights and dynamic SQL, enable you to build reusable application subcomponents that can operate on and access the invoker's data and modules.

A Dynamic SQL Scenario Using Native Dynamic SQL

This scenario shows you how to perform the following operations using native dynamic SQL:

• Execute DDL and DML operations
• Execute single row and multiple row queries

The database in this scenario is a company's human resources database (named hr) with the following data model:

A master table named offices contains the list of all company locations. The offices table has the following definition:

Column Name          Null?          Type         
LOCATION             NOT_NULL       VARCHAR2(200)

Multiple emp_location tables contain the employee information, where location is the name of city where the office is located. For example, a table named emp_houston contains employee information for the company's Houston office, while a table named emp_boston contains employee information for the company's Boston office.

Each emp_location table has the following definition:

Column Name          Null?          Type         
EMPNO                NOT_NULL       NUMBER(4)
ENAME                NOT_NULL       VARCHAR2(10)
JOB                  NOT_NULL       VARCHAR2(9)
SAL                  NOT_NULL       NUMBER(7,2)
DEPTNO               NOT_NULL       NUMBER(2)

The following sections describe various native dynamic SQL operations that can be performed on the data in the hr database.

Sample DML Operation Using Native Dynamic SQL

The following native dynamic SQL procedure gives a raise to all employees with a particular job title:

CREATE OR REPLACE PROCEDURE salary_raise (raise_percent NUMBER, job VARCHAR2) IS
    TYPE loc_array_type IS TABLE OF VARCHAR2(40)
        INDEX BY binary_integer;
    dml_str VARCHAR2        (200);
    loc_array    loc_array_type;
BEGIN
    -- bulk fetch the list of office locations
    SELECT location BULK COLLECT INTO loc_array
        FROM offices;
    -- for each location, give a raise to employees with the given 'job' 
    FOR i IN loc_array.first..loc_array.last LOOP
        dml_str := 'UPDATE emp_' || loc_array(i) 
        || ' SET sal = sal * (1+(:raise_percent/100))'
        || ' WHERE job = :job_title';
    EXECUTE IMMEDIATE dml_str USING raise_percent, job;
    END LOOP;
END;
/
SHOW ERRORS;

Sample DDL Operation Using Native Dynamic SQL

The EXECUTE IMMEDIATE statement can perform DDL operations. For example, the following procedure adds an office location:

CREATE OR REPLACE PROCEDURE add_location (loc VARCHAR2) IS
BEGIN
    -- insert new location in master table
    INSERT INTO offices VALUES (loc);
    -- create an employee information table
    EXECUTE IMMEDIATE  
    'CREATE TABLE ' || 'emp_' || loc ||
    '( 
        empno   NUMBER(4) NOT NULL,
        ename   VARCHAR2(10),
        job     VARCHAR2(9),
        sal     NUMBER(7,2),
        deptno  NUMBER(2) 
    )';
END;
/
SHOW ERRORS;

The following procedure deletes an office location:

CREATE OR REPLACE PROCEDURE drop_location (loc VARCHAR2) IS
BEGIN
    -- delete the employee table for location 'loc'
    EXECUTE IMMEDIATE 'DROP TABLE ' || 'emp_' || loc;
    -- remove location from master table
    DELETE FROM offices WHERE location = loc;
END;
/
SHOW ERRORS;

Sample Single-Row Query Using Native Dynamic SQL

The EXECUTE IMMEDIATE statement can perform dynamic single-row queries. You can specify bind variables in the USING clause and fetch the resulting row into the target specified in the INTO clause of the statement.

The following function retrieves the number of employees at a particular location performing a specified job:

CREATE OR REPLACE FUNCTION get_num_of_employees (loc VARCHAR2, job VARCHAR2) 
    RETURN NUMBER IS
    query_str VARCHAR2(1000);
    num_of_employees NUMBER;
BEGIN
    query_str := 'SELECT COUNT(*) FROM '
        || ' emp_' || loc
        || ' WHERE job = :job_title';
    EXECUTE IMMEDIATE query_str
        INTO num_of_employees
        USING job;
    RETURN num_of_employees;
END;
/
SHOW ERRORS;

Sample Multiple-Row Query Using Native Dynamic SQL

The OPEN-FOR, FETCH, and CLOSE statements can perform dynamic multiple-row queries. For example, the following procedure lists all of the employees with a particular job at a specified location:

CREATE OR REPLACE PROCEDURE list_employees(loc VARCHAR2, job VARCHAR2) IS
    TYPE cur_typ IS REF CURSOR;
    c           cur_typ;
    query_str   VARCHAR2(1000);
    emp_name    VARCHAR2(20);
    emp_num     NUMBER;
BEGIN
    query_str := 'SELECT ename, empno FROM emp_' || loc 
        || ' WHERE job = :job_title';
    -- find employees who perform the specified job
    OPEN c FOR query_str USING job;
    LOOP
        FETCH c INTO emp_name, emp_num;
        EXIT WHEN c%NOTFOUND;
        -- process row here
    END LOOP;
    CLOSE c;
END;
/
SHOW ERRORS;

Choosing Between Native Dynamic SQL and the DBMS_SQL Package

Oracle provides two methods for using dynamic SQL within PL/SQL: native dynamic SQL and the DBMS_SQL package. Native dynamic SQL lets you place dynamic SQL statements directly into PL/SQL code. These dynamic statements include DML statements (including queries), PL/SQL anonymous blocks, DDL statements, transaction control statements, and session control statements.

To process most native dynamic SQL statements, you use the EXECUTE IMMEDIATE statement. To process a multi-row query (SELECT statement), you use OPEN-FOR, FETCH, and CLOSE statements.

The DBMS_SQL package is a PL/SQL library that offers an API to execute SQL statements dynamically. The DBMS_SQL package has procedures to open a cursor, parse a cursor, supply binds, and so on. Programs that use the DBMS_SQL package make calls to this package to perform dynamic SQL operations.

The following sections provide detailed information about the advantages of both methods.

Advantages of Native Dynamic SQL

Native dynamic SQL provides the following advantages over the DBMS_SQL package:

Native Dynamic SQL is Easy to Use

Because native dynamic SQL is integrated with SQL, you can use it in the same way that you use static SQL within PL/SQL code. Native dynamic SQL code is typically more compact and readable than equivalent code that uses the DBMS_SQL package.

With the DBMS_SQL package you must call many procedures and functions in a strict sequence, making even simple operations require a lot of code. You can avoid this complexity by using native dynamic SQL instead.

Table 8-1 illustrates the difference in the amount of code required to perform the same operation using the DBMS_SQL package and native dynamic SQL.

Table 8-1 Code Comparison of DBMS_SQL Package and Native Dynamic SQL

CREATE PROCEDURE insert_into_table (
      table_name  VARCHAR2, 
      deptnumber  NUMBER, 
      deptname    VARCHAR2, 
      location    VARCHAR2) IS
   cur_hdl         INTEGER;
   stmt_str        VARCHAR2(200);
   rows_processed  BINARY_INTEGER;

BEGIN
   stmt_str := 'INSERT INTO ' || 
      table_name || ' VALUES 
      (:deptno, :dname, :loc)';

   -- open cursor
   cur_hdl := dbms_sql.open_cursor;

   -- parse cursor
   dbms_sql.parse(cur_hdl, stmt_str,
      dbms_sql.native);

   -- supply binds
   dbms_sql.bind_variable
      (cur_hdl, ':deptno', deptnumber);
   dbms_sql.bind_variable
      (cur_hdl, ':dname', deptname);
   dbms_sql.bind_variable
      (cur_hdl, ':loc', location);

    -- execute cursor
    rows_processed := 
    dbms_sql.execute(cur_hdl);

    -- close cursor
    dbms_sql.close_cursor(cur_hdl);

END;
/
SHOW ERRORS;

CREATE PROCEDURE insert_into_table (
      table_name  VARCHAR2, 
      deptnumber  NUMBER, 
      deptname    VARCHAR2, 
      location    VARCHAR2) IS
   stmt_str    VARCHAR2(200);

BEGIN
   stmt_str := 'INSERT INTO ' || 
      table_name || ' values 
      (:deptno, :dname, :loc)';

   EXECUTE IMMEDIATE stmt_str 
      USING 
      deptnumber, deptname, location;

END;
/
SHOW ERRORS;

Native Dynamic SQL is Faster than DBMS_SQL

Native dynamic SQL in PL/SQL performs comparably to the performance of static SQL, because the PL/SQL interpreter has built-in support for it. Programs that use native dynamic SQL are much faster than programs that use the DBMS_SQL package. Typically, native dynamic SQL statements perform 1.5 to 3 times better than equivalent DBMS_SQL calls. (Your performance gains may vary depending on your application.)

Native dynamic SQL bundles the statement preparation, binding, and execution steps into a single operation, which minimizes the data copying and procedure call overhead and improves performance.

The DBMS_SQL package is based on a procedural API and incurs high procedure call and data copy overhead. Each time you bind a variable, the DBMS_SQL package copies the PL/SQL bind variable into its space for use during execution. Each time you execute a fetch, the data is copied into the space managed by the DBMS_SQL package and then the fetched data is copied, one column at a time, into the appropriate PL/SQL variables, resulting in substantial overhead.

Performance Tip: Using Bind Variables

When using either native dynamic SQL or the DBMS_SQL package, you can improve performance by using bind variables, because bind variables allow Oracle to share a single cursor for multiple SQL statements.

For example, the following native dynamic SQL code does not use bind variables:

CREATE OR REPLACE PROCEDURE del_dept (
   my_deptno  dept.deptno%TYPE) IS
BEGIN
   EXECUTE IMMEDIATE 'DELETE FROM dept WHERE deptno = ' || to_char (my_deptno);
END;
/
SHOW ERRORS;

For each distinct my_deptno variable, a new cursor is created, causing resource contention and poor performance. Instead, bind my_deptno as a bind variable:

CREATE OR REPLACE PROCEDURE del_dept (
   my_deptno  dept.deptno%TYPE) IS
BEGIN
   EXECUTE IMMEDIATE 'DELETE FROM dept WHERE deptno = :1' USING my_deptno;
END;
/
SHOW ERRORS;

Here, the same cursor is reused for different values of the bind my_deptno, improving performance and scalabilty.

Native Dynamic SQL Supports User-Defined Types

Native dynamic SQL supports all of the types supported by static SQL in PL/SQL, including user-defined types such as user-defined objects, collections, and REFs. The DBMS_SQL package does not support these user-defined types.

Native Dynamic SQL Supports Fetching Into Records

Native dynamic SQL and static SQL both support fetching into records, but the DBMS_SQL package does not. With native dynamic SQL, the rows resulting from a query can be directly fetched into PL/SQL records.

In the following example, the rows from a query are fetched into the emp_rec record:

DECLARE
    TYPE EmpCurTyp IS REF CURSOR;
    c EmpCurTyp;
    emp_rec emp%ROWTYPE;
    stmt_str VARCHAR2(200);
    e_job emp.job%TYPE;

BEGIN
   stmt_str := 'SELECT * FROM emp WHERE job = :1';
    -- in a multi-row query
    OPEN c FOR stmt_str USING 'MANAGER';
    LOOP
        FETCH c INTO emp_rec;
        EXIT WHEN c%NOTFOUND;
    END LOOP;
    CLOSE c;
    -- in a single-row query
    EXECUTE IMMEDIATE stmt_str INTO emp_rec USING 'PRESIDENT';

END;
/

Advantages of the DBMS_SQL Package

The DBMS_SQL package provides the following advantages over native dynamic SQL:

DBMS_SQL is Supported in Client-Side Programs

The DBMS_SQL package is supported in client-side programs, but native dynamic SQL is not. Every call to the DBMS_SQL package from the client-side program translates to a PL/SQL remote procedure call (RPC); these calls occur when you need to bind a variable, define a variable, or execute a statement.

DBMS_SQL Supports DESCRIBE

The DESCRIBE_COLUMNS procedure in the DBMS_SQL package can be used to describe the columns for a cursor opened and parsed through DBMS_SQL. This feature is similar to the DESCRIBE command in SQL*Plus. Native dynamic SQL does not have a DESCRIBE facility.

DBMS_SQL Supports Multiple Row Updates and Deletes with a RETURNING Clause

The DBMS_SQL package supports statements with a RETURNING clause that update or delete multiple rows. Native dynamic SQL only supports a RETURNING clause if a single row is returned.

DBMS_SQL Supports SQL Statements Larger than 32KB

The DBMS_SQL package supports SQL statements larger than 32KB; native dynamic SQL does not.

DBMS_SQL Lets You Reuse SQL Statements

The PARSE procedure in the DBMS_SQL package parses a SQL statement once. After the initial parsing, you can use the statement multiple times with different sets of bind arguments.

Native dynamic SQL prepares a SQL statement each time the statement is used, which typically involves parsing, optimization, and plan generation. Although the extra prepare operations incur a small performance penalty, the slowdown is typically outweighed by the performance benefits of native dynamic SQL.

Examples of DBMS_SQL Package Code and Native Dynamic SQL Code

The following examples illustrate the differences in the code necessary to complete operations with the DBMS_SQL package and native dynamic SQL. Specifically, the following types of examples are presented:

• A query
• A DML operation
• A DML returning operation

In general, the native dynamic SQL code is more readable and compact, which can improve developer productivity.

Querying Using Dynamic SQL: Example

The following example includes a dynamic query statement with one bind variable (:jobname) and two select columns (ename and sal):

stmt_str := 'SELECT ename, sal FROM emp WHERE job = :jobname';

This example queries for employees with the job description SALESMAN in the job column of the emp table. Table 8-2 shows sample code that accomplishes this query using the DBMS_SQL package and native dynamic SQL.

Table 8-2 Querying Using the DBMS_SQL Package and Native Dynamic SQL

DECLARE  
  stmt_str varchar2(200);
  cur_hdl int;
  rows_processed int;
  name varchar2(10);
  salary int;
BEGIN
cur_hdl := dbms_sql.open_cursor; -- open cursor 
stmt_str := 'SELECT ename, sal FROM emp WHERE 
job = :jobname';
dbms_sql.parse(cur_hdl, stmt_str, 
dbms_sql.native); 

-- supply binds (bind by name) 
dbms_sql.bind_variable(
  cur_hdl, 'jobname', 'SALESMAN'); 

-- describe defines 
dbms_sql.define_column(cur_hdl, 1, name, 200); 
dbms_sql.define_column(cur_hdl, 2, salary); 

rows_processed := dbms_sql.execute(cur_hdl); -- 
execute 

LOOP 
  -- fetch a row 
  IF dbms_sql.fetch_rows(cur_hdl) > 0 then 

    -- fetch columns from the row 
    dbms_sql.column_value(cur_hdl, 1, name); 
    dbms_sql.column_value(cur_hdl, 2, salary); 

    -- <process data> 

      ELSE
        EXIT; 
      END IF; 
END LOOP; 
dbms_sql.close_cursor(cur_hdl); -- close cursor
END;
/

DECLARE
  TYPE EmpCurTyp IS REF CURSOR;
  cur EmpCurTyp;
  stmt_str VARCHAR2(200);
  name VARCHAR2(20);
  salary NUMBER;
BEGIN
  stmt_str := 'SELECT ename, sal FROM emp 
    WHERE job = :1';
  OPEN cur FOR stmt_str USING 'SALESMAN'; 

LOOP
  FETCH cur INTO name, salary; 
  EXIT WHEN cur%NOTFOUND; 
  -- <process data>  
END LOOP; 
CLOSE cur;
END;
/

Performing DML Using Dynamic SQL: Example

The following example includes a dynamic INSERT statement for a table with three columns:

stmt_str := 'INSERT INTO dept_new VALUES (:deptno, :dname, :loc)';

This example inserts a new row for which the column values are in the PL/SQL variables deptnumber, deptname, and location. Table 8-3 shows sample code that accomplishes this DML operation using the DBMS_SQL package and native dynamic SQL.

Table 8-3 DML Operation Using the DBMS_SQL Package and Native Dynamic SQL

DECLARE
  stmt_str VARCHAR2(200);
  cur_hdl NUMBER;
  deptnumber NUMBER := 99;
  deptname VARCHAR2(20);
  location VARCHAR2(10);
  rows_processed NUMBER;
BEGIN
  stmt_str := 'INSERT INTO dept_new VALUES 
    (:deptno, :dname, :loc)';
  cur_hdl := DBMS_SQL.OPEN_CURSOR;
  DBMS_SQL.PARSE(
    cur_hdl, stmt_str, DBMS_SQL.NATIVE);
    -- supply binds
  DBMS_SQL.BIND_VARIABLE
    (cur_hdl, ':deptno', deptnumber);
  DBMS_SQL.BIND_VARIABLE
    (cur_hdl, ':dname', deptname);
  DBMS_SQL.BIND_VARIABLE
    (cur_hdl, ':loc', location);
    rows_processed := dbms_sql.execute(cur_hdl);  
    -- execute
  DBMS_SQL.CLOSE_CURSOR(cur_hdl); -- close
END;
/

DECLARE
  stmt_str VARCHAR2(200);
  deptnumber NUMBER := 99;
  deptname VARCHAR2(20);
  location VARCHAR2(10);
BEGIN
  stmt_str := 'INSERT INTO dept_new VALUES  
  (:deptno, :dname, :loc)';
  EXECUTE IMMEDIATE stmt_str 
    USING deptnumber, deptname, location;
END;
/

Performing DML with RETURNING Clause Using Dynamic SQL: Example

The following example uses a dynamic UPDATE statement to update the location of a department, then returns the name of the department:

stmt_str := 'UPDATE dept_new 
            SET loc = :newloc
            WHERE deptno = :deptno
            RETURNING dname INTO :dname';

Table 8-4 shows sample code that accomplishes this operation using both the DBMS_SQL package and native dynamic SQL.

Table 8-4 DML Returning Operation Using the DBMS_SQL Package and Native Dynamic SQL

DECLARE 
  deptname_array dbms_sql.Varchar2_Table; 
  cur_hdl INT;
  stmt_str VARCHAR2(200);
  location VARCHAR2(20);
  deptnumber NUMBER := 10;
  rows_processed NUMBER;
BEGIN 
 stmt_str := 'UPDATE dept_new 
    SET loc = :newloc
    WHERE deptno = :deptno
    RETURNING dname INTO :dname';
    
  cur_hdl := dbms_sql.open_cursor; 
  dbms_sql.parse
    (cur_hdl, stmt_str, dbms_sql.native); 
  -- supply binds 
  dbms_sql.bind_variable
    (cur_hdl, ':newloc', location); 
  dbms_sql.bind_variable
    (cur_hdl, ':deptno', deptnumber); 
  dbms_sql.bind_array
    (cur_hdl, ':dname', deptname_array); 
  -- execute cursor 
  rows_processed := dbms_sql.execute(cur_hdl); 
  -- get RETURNING column into OUT bind array 
  dbms_sql.variable_value
    (cur_hdl, ':dname', deptname_array); 
  dbms_sql.close_cursor(cur_hdl); 
END;
/

DECLARE 
  deptname_array dbms_sql.Varchar2_Table; 
  stmt_str  VARCHAR2(200);
  location  VARCHAR2(20);
  deptnumber NUMBER := 10;
  deptname   VARCHAR2(20);
BEGIN
  stmt_str := 'UPDATE dept_new 
    SET loc = :newloc
    WHERE deptno = :deptno
    RETURNING dname INTO :dname';
  EXECUTE IMMEDIATE stmt_str 
    USING location, deptnumber, OUT deptname;
END;
/

Using Dynamic SQL in Languages Other Than PL/SQL

Although this chapter discusses PL/SQL support for dynamic SQL, you can call dynamic SQL from other languages:

• If you use C/C++, you can call dynamic SQL with the Oracle Call Interface (OCI), or you can use the Pro*C/C++ precompiler to add dynamic SQL extensions to your C code.
• If you use COBOL, you can use the Pro*COBOL precompiler to add dynamic SQL extensions to your COBOL code.
• If you use Java, you can develop applications that use dynamic SQL with JDBC.

If you have an application that uses OCI, Pro*C/C++, or Pro*COBOL to execute dynamic SQL, you should consider switching to native dynamic SQL inside PL/SQL stored procedures and functions. The network round-trips required to perform dynamic SQL operations from client-side applications might hurt performance. Stored procedures can reside on the server, eliminating the network overhead. You can call the PL/SQL stored procedures and stored functions from the OCI, Pro*C/C++, or Pro*COBOL application.

Using PL/SQL Records in SQL INSERT and UPDATE Statements

Although you can enumerate each field of a PL/SQL record when inserting or updating rows in a table, the resulting code is not especially readable or maintainable. Instead, you can use PL/SQL records directly in these statements. The most convenient technique is to declare the record using a %ROWTYPE attribute, so that it has exactly the same fields as the SQL table.

DECLARE
    emp_rec emp%ROWTYPE;
BEGIN
   emp_rec.eno := 1500;
   emp_rec.ename := 'Steven Hill';
   emp_rec.sal := '40000';
-- A %ROWTYPE value can fill in all the row fields.
    INSERT INTO emp VALUES emp_rec;

-- The fields of a %ROWTYPE can completely replace the table columns.
    UPDATE emp SET ROW = emp_rec WHERE eno = 100;
END;
/

Although this technique helps to integrate PL/SQL variables and types more closely with SQL DML statements, you cannot use PL/SQL records as bind variables in dynamic SQL statements.