Cast multiset

Question

How does cast multiset work, I have a huge sql whcih is returning one value say p_opp_id ( on the basis of this i need few more coumns) , i was suggested to use cast multiset , what is cast multiset and how it works

Answer 1

CAST(MULTISET(subquery) AS collection_type) converts the result of a subquery into a collection.
An example I had lying around:
CREATE TABLE master (table_name PRIMARY KEY) AS
SELECT table_name
FROM   user_tables;
CREATE TABLE detail AS
SELECT table_name, column_name, data_type
FROM   user_tab_columns;
CREATE OR REPLACE TYPE name_strvalue_ot AS OBJECT
( name VARCHAR2(30)
, value VARCHAR2(50) );
CREATE OR REPLACE TYPE name_strvalue_tt AS TABLE OF name_strvalue_ot;
SELECT m.table_name
     , CAST(
       MULTISET
       ( SELECT name_strvalue_ot(d.column_name, d.data_type)
         FROM   detail d
         WHERE  d.table_name = m.table_name
       ) AS name_strvalue_tt) cols
FROM   master m;
BEGIN
     FOR r IN
          SELECT m.table_name
               , CAST(
                 MULTISET
                 ( SELECT name_strvalue_ot(d.column_name, d.data_type)
                   FROM   detail d
                   WHERE  d.table_name = m.table_name
                 ) AS name_strvalue_tt) cols
          FROM   master m
     LOOP
          DBMS_OUTPUT.PUT_LINE(r.table_name || ': ' || r.cols.count || ' columns');
     END LOOP;
END;
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