Oracle: update multiple columns with dynamic query - database

Question

I am trying to update all the columns of type NVARCHAR2 to some random string in my database. I iterated through all the columns in the database of type nvarchar2 and executed an update statement for each column.
for i in (
select
table_name,
column_name
from
user_tab_columns
where
data_type = 'NVARCHAR2'
) loop
execute immediate
'update ' || i.table_name || 'set ' || i.column_name ||
' = DBMS_RANDOM.STRING(''X'', length('|| i.column_name ||'))
where ' || i.column_name || ' is not null';
Instead of running an update statement for every column of type nvarchar2, I want to update all the nvarchar columns of a particular table with a single update statement for efficiency(that is, one update statement per 1 table). For this, I tried to bulk collect all the nvarchar columns in a table, into a temporary storage. But, I am stuck at writing a dynamic update statement for this. Could you please help me with this? Thanks in advance!

Answer 1

You can try this one. However, depending on your table it could be not the fastest solution.
for aTable in (
select table_name,
listagg(column_name||' = nvl2('||column_name||', DBMS_RANDOM.STRING(''XX'', length('||column_name||')), NULL)') WITHIN GROUP (ORDER BY column_name) as upd,
listagg(column_name) WITHIN GROUP (ORDER BY column_name) as con
from user_tab_columns
where DATA_TYPE = 'NVARCHAR2'
group by table_name
) loop
execute immediate
'UPDATE '||aTable.table_name ||
' SET '||aTable.upd ||
' WHERE COALESCE('||aTable.con||') IS NOT NULL';
end loop;
Resulting UPDATE (verify with DBMS_OUTPUT.PUT_LINE(..)) should look like this:
UPDATE MY_TABLE SET
COL_A = nvl2(COL_A, DBMS_RANDOM.STRING('XX', length(COL_A)), NULL),
COL_B = nvl2(COL_B, DBMS_RANDOM.STRING('XX', length(COL_B)), NULL)
WHERE COALESCE(COL_A, COL_B) IS NOT NULL;

Answer 2

Please try this:
DECLARE
CURSOR CUR IS
SELECT
TABLE_NAME,
LISTAGG(COLUMN_NAME||' = DBMS_RANDOM.STRING(''X'', length(NVL('||
COLUMN_NAME ||',''A''))',', ')
WITHIN GROUP (ORDER BY COLUMN_ID) COLUMN_NAME
FROM DBA_TAB_COLUMNS
WHERE DATA_TYPE = 'NVARCHAR2'
GROUP BY TABLE_NAME;
TYPE TAB IS TABLE OF CUR%ROWTYPE INDEX BY PLS_INTEGER;
T TAB;
S VARCHAR2(4000);
BEGIN
OPEN CUR;
LOOP
FETCH CUR BULK COLLECT INTO T LIMIT 1000;
EXIT WHEN T.COUNT = 0;
FOR i IN 1..T.COUNT LOOP
S := 'UPDATE ' || T(i).TABLE_NAME || ' SET ' || T(i).COLUMN_NAME;
EXECUTE IMMEDIATE S;
END LOOP;
END LOOP;
COMMIT;
END;
/

Answer 3

I think that would do it. But as I said in the comments, you need to validate the syntax since I don't have an Oracle instance to test it.
for i in (
select table_name,
'update || i.table_name || set ' ||
listagg( column_name || '= NLV( ' || column_name || ', '
|| 'DBMS_RANDOM.STRING(''X'', length('|| column_name ||') ) )'
|| ';'
) WITHIN GROUP (ORDER BY column_name) as updCommand
from user_tab_columns
where DATA_TYPE = 'NVARCHAR2'
group by table_name
) loop
execute immediate i.updCommand;
end loop;
If you find any error, let me know in the comments so I can fix it.