Open cursor for dynamic table name in PL/SQL procedure - oracle

Question

I want to create procedure, that will use cursor, which is the same for arbitrary tables. My current one looks like this:
create or replace
PROCEDURE
some_name(
p_talbe_name IN VARCHAR2,
p_chunk_size IN NUMBER,
p_row_limit IN NUMBER
) AS
CURSOR v_cur IS
SELECT common_column,
ora_hash(substr(common_column, 1, 15), p_chunk_size) as chunk_number
-- Here it can find the table!
FROM p_table_name;
TYPE t_sample IS TALBE OF v_cur%rowtype;
v_sample t_sample;
BEGIN
OPEN v_cur;
LOOP FETCH v_cur BULK COLLECT INTO v_sample LIMIT p_row_limit;
FORALL i IN v_sample.first .. v_sample.last
INSERT INTO chunks VALUES v_sample(i);
COMMIT;
EXIT WHEN v_cur%notfound;
END LOOP;
CLOSE v_cur;
END;
The problem is that it cannot find the table named p_table_name which I want to parametrize. The thing is that I need to create chunks based on hashes for common_column which exists in all intended tables. How to deal with that problem? Maybe there is the equivalent oracle code that will do the same thing? Then I need the same efficiency for the query. Thanks!

Answer 1

I would do this as a single insert-as-select statement, complicated only by the fact you're passing in the table_name, so we need to use dynamic sql.
I would do it something like:
CREATE OR REPLACE PROCEDURE some_name(p_table_name IN VARCHAR2,
p_chunk_size IN NUMBER,
p_row_limit IN NUMBER) AS
v_table_name VARCHAR2(32); -- 30 characters for the tablename, 2 for doublequotes in case of case sensitive names, e.g. "table_name"
v_insert_sql CLOB;
BEGIN
-- Sanitise the passed in table_name, to ensure it meets the rules for being an identifier name. This is to avoid SQL injection in the dynamic SQL
-- statement we'll be using later.
v_table_name := DBMS_ASSERT.ENQUOTE_LITERAL(p_table_name);
v_insert_sql := 'insert into chunks (common_column_name, chunk_number)'||CHR(10)|| -- replace the column names with the actual names of your chunks table columns.
'select common_column,'||CHR(10)||
' ora_hash(substr(common_column, 1, 15), :p_chunk_size) AS chunk_number'||CHR(10)||
'from '||v_table_name||CHR(10)||
'where rownum <= :p_row_limit';
-- Used for debug purposes, so you can see the definition of the statement that's going to be run.
-- Remove before putting the code in production / convert to proper logging code:
dbms_output.put_line(v_insert_sql);
-- Now run the statement:
EXECUTE IMMEDIATE v_insert_sql USING p_chunk_size, p_row_limit;
-- I've included the p_row_limit in the above statement, since I'm not sure if your original code loops through all the rows once it processes the
-- first p_row_limit rows. If you need to insert all rows from the p_table_name into the chunks table, remove the predicate from the insert sql and the extra bind variable passed into the execute immediate.
END some_name;
/
By using a single insert-as-select statement, you are using the most efficient way of doing the work. Doing the bulk collect (which you were using) would use up memory (storing the data in the array) and cause extra context switches between the PL/SQL and SQL engines that the insert-as-select statement avoids.