Dynamically look up column names for a table while in an sql query
Question
I'm writing SQL (for Oracle) like:
INSERT INTO Schema1.tableA SELECT * FROM Schema2.tableA;
where Schema1.tableA and Schema2.tableA have the same columns. However, it seems like this is unsafe, since the order of the columns coming back in the SELECT is undefined. What I should be doing is:
INSERT INTO Schema1.tableA (col1, col2, ... colN) SELECT (col1, col2, ... colN) FROM Schema2.tableA;
I'm doing this for lots of tables using some scripts, so what I'd like to do is write something like:
INSERT INTO Schema1.tableA (foo(Schema1.tableA)) SELECT (foo(Schema1.tableA)) FROM Schema2.tableA;
Where foo is some nifty magic that extracts the column names from table one and packages them in the appropriate syntax. Thoughts?
Solution
This PL/SQL should do it:
declare
l_cols long;
l_sql long;
begin
for r in (select column_name from all_tab_columns
where table_name = 'TABLEA'
and owner = 'SCHEMA1'
)
loop
l_cols := l_cols || ',' || r.column_name;
end loop;
-- Remove leading comma
l_cols := substr(l_cols, 2);
l_sql := 'insert into schema1.tableA (' || l_cols || ') select '
|| l_cols || ' from schema2.tableA';
execute immediate l_sql;
end;
/
OTHER TIPS
You may need to construct the insert statements dynamically using USER_TAB_COLUMNS and execute them using EXECUTE IMMEDIATE.
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