Building a Dynamic SQL Statement

Question:  I have a motor vehicle application where I need to build a SQL statement based on the presence of NOT NULL values on an input screen.  I am collecting the following screen values; license_plate_nbr, color, vehicle_make, vehicle_model and vehicle_type. 

 How do I build and execute a dynamic SQL statement?

Answer:  You can write a stored procedure that uses the EXECUTE IMMEDIATE function to execute a dynamic SQL statement.  The parameters are positional based on a prototype:

exec vehicle_query(
    license_plate_nbr,
    vehicle_primary_color,
    vehicle_make,
    vehicle_model,
    vehicle_type);

For example, the following is the query to display all blue Ford cars. 

Note that all omitted characters are designated by a comma:

 exec vehicle_query( ,'Blue', 'Ford',,);

 Next we need to build a SQL statement that adds WHERE clause predicates based on the presence or absence of the passed arguments.   

Note:  This is pseudocode, not tested:

create or replace procedure
   vehicle_query
as
BEGIN
   i_license_nbr           varchar2(8),
   i_vehicle_primary_color varchar2(10),
   i_vehicle_make          varchar2(10),
   i_vehicle_make          varchar2(10),
   i_vehicle_model         varchar2(10),
   i_vehicle_type          varchar2(10),
   sql_str                 varchar2(100) := '';
BEGIN

-- Initialize the SQL statement with everything bit the end semicolon

sql_str := 'select * from vehicle where 1=1'

-- Here, be careful to get the quote marks to resolve properly

if i_license_nbr is not null then

   sql_str := sql_str|| ' and vehicle_license_nbr contains('%:i_license_nbr%')'

if i_vehicle_primary_color is not null then
   sql_str := sql_str|| ' and vehicle_primary_color = ':i_vehicle_license_nbr')'

-- etc.

-- end the sql statement

sql_str = sql_str||';'

-- verify the SQL

dbms_output.put_line(:sql_str);

-- execute the sql:

execute immediate(:sql_str);
END
/;  

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