Inserting multiple rows into Oracle

Question

In the discussion about multiple row insert into the Oracle two approaches were demonstrated:

First:

insert into pager (PAG_ID,PAG_PARENT,PAG_NAME,PAG_ACTIVE)
          select 8000,0,'Multi 8000',1 from dual
union all select 8001,0,'Multi 8001',1 from dual

Second:

INSERT ALL
   INTO t (col1, col2, col3) VALUES ('val1_1', 'val1_2', 'val1_3')
   INTO t (col1, col2, col3) VALUES ('val2_1', 'val2_2', 'val2_3')
   INTO t (col1, col2, col3) VALUES ('val3_1', 'val3_2', 'val3_3')
   .
   .
   .
SELECT 1 FROM DUAL;

Could anyone argue the preference of using one over another?

P.S. I didn't do any research myself (even explanation plan), so any information or opinion would be appreciated.

Thanks.

Answer 1

The INSERT ALL method has a problem with inserting bigger number of rows into a table.

I recently wanted to insert 1130 rows into a table with single SQL statement. When I tried to do this with INSERT ALL method I got the following error:

ORA-24335 - cannot support more than 1000 columns

When I used INSERT INTO .. UNION ALL .. approach everything went fine.

Btw. I didn't know about the UNION ALL method before I found this discussion :)

Answer 2

From performance's point of view, these queries are identical.

UNION ALL won't hurt performance, since Oracle estimates the UNION'ed query only when it needs it, it doesn't cache the results first.

SELECT syntax is more flexible in that sense that you can more easuly manupulate the SELECT query if you want to change something.

For instance, this query:

insert into pager (PAG_ID,PAG_PARENT,PAG_NAME,PAG_ACTIVE)
          select 8000,0,'Multi 8000',1 from dual
union all select 8001,0,'Multi 8001',1 from dual

can be rewritten as

INSERT
INTO    pager (PAG_ID,PAG_PARENT,PAG_NAME,PAG_ACTIVE)
SELECT  7999 + level, 0, 'Multi ' || 7999 + level, 1
FROM    dual
CONNECT BY
        level <= 2

By replacing 2 with appropriate number, you can get any number of rows you want.

In case of INSERT ALL, you would have to duplicate the destination table description, which is less readable if you need, say, 40 rows.