INSERT INTO vs SELECT INTO

Question

What is the difference between using  SELECT     INTO MyTable FROM      and  INSERT INTO MyTable       SELECT     FROM           From BOL   INSERT  SELECT   INTO    I know that using SELECT   INTO will create the insertion table on the default file group if it doesn t already exist  and that the logging for this statement depends on the recovery model of the database    Which statement is preferable   Are there other performance implications  What is a good use case for SELECT   INTO over INSERT INTO        Edit  I already stated that I know that that SELECT INTO    creates a table where it doesn t exist   What I want to know is that SQL includes this statement for a reason  what is it  Is it doing something different behind the scenes for inserting rows  or is it just syntactic sugar on top of a CREATE TABLE and INSERT INTO

User · Answer

Which statement is preferable   Depends on what you are doing  Are there other performance implications  If the table is a permanent table  you can create indexes at the time of table creation which has implications for performance both negatively and positiviely  Select into does not recreate indexes that exist on current tables and thus subsequent use of the table may be slower than it needs to be  What is a good use case for SELECT   INTO over INSERT INTO      Select into is used if you may not know the table structure in advance  It is faster to write than create table and an insert statement  so it is used to speed up develoment at times  It is often faster to use when you are creating a quick temp table to test things or a backup table of a specific query  maybe records you are going to delete   It should be rare to see it used in production code that will run multiple times   except for temp tables  because it will fail if the table was already in existence      It is sometimes used inappropriately by people who don t know what they are doing  And they can cause havoc in the db as a result  I strongly feel it is inappropriate to use SELECT INTO for anything other than a throwaway table  a temporary backup  a temp table that will go away at the end of the stored proc  etc    Permanent tables need real thought as to their design and SELECT INTO makes it easy to avoid thinking about anything even as basic as what columns and what datatypes   In general  I prefer the use of the create table and insert statement - you have more controls and it is better for repeatable processes  Further  if the table is a permanent table  it should be created from a separate create table script  one that is in source control  as creating permanent objects should not  in general  in code are inserts deletes updates or selects from a table  Object changes should be handled separately from data changes because objects have implications beyond the needs of a specific insert update select delete  You need to consider the best data types  think about FK constraints  PKs and other constraints  consider auditing requirements  think about indexing  etc

User · Answer

The simple difference between select Into and Insert Into is  --  Select Into don t need existing table  If you want to copy table A data  you just type Select   INTO  tablename  from A  Here  tablename can be existing table or new table will be created which has same structure like table A   --  Insert Into do need existing table INSERT INTO  tablename  SELECT   FROM A   Here tablename is an existing table   Select Into is usually more popular to copy data especially backup data   You can use as per your requirement  it is totally developer choice which should be used in his scenario   Performance wise Insert INTO is fast   References    https   www w3schools com sql sql insert into select asp https   www w3schools com sql sql select into asp

User · Answer

I only want to cover second point of the question that is related to performance  because no body else has covered this  Select Into is a lot more faster than insert into  when it comes to tables with large datasets  I prefer select into when I have to read a very large table  insert into for a table with 10 million rows may take hours while select into will do this in minutes  and as for as losing indexes on new table is concerned you can recreate the indexes by query and can still save a lot more time when compared to insert into

User · Answer

SELECT INTO is typically used to generate temp tables or to copy another table  data and or structure     In day to day code you use INSERT because your tables should already exist to be read  UPDATEd  DELETEd  JOINed etc  Note  the INTO keyword is optional with INSERT  That is  applications won t normally create and drop tables as part of normal operations unless it is a temporary table for some scope limited and specific usage   A table created by SELECT INTO will have no keys or indexes or constraints unlike a real  persisted  already existing table  The 2 aren t directly comparable because they have almost no overlap in usage

User · Answer

Select into creates new table for you at the time and then insert records in it from the source table  The newly created table has the same structure as of the source table If you try to use select into for a existing table it will produce a error  because it will try to create new table with the same name  Insert into requires the table to be exist in your database before you insert rows in it

User · Answer

Actually SELECT     INTO not only creates the table but will fail if it already exists  so basically the only time you would use it is when the table you are inserting to does not exists   In regards to your EDIT   I personally mainly use SELECT     INTO when I am creating a temp table  That to me is the main use  However I also use it when creating new tables with many columns with similar structures to other tables and then edit it in order to save time

User · Answer

The primary difference is that SELECT INTO MyTable will create a new table called MyTable with the results  while INSERT INTO requires that MyTable already exists   You would use SELECT INTO only in the case where the table didn t exist and you wanted to create it based on the results of your query  As such  these two statements really are not comparable  They do very different things   In general  SELECT INTO is used more often for one off tasks  while INSERT INTO is used regularly to add rows to tables   EDIT  While you can use CREATE TABLE and INSERT INTO to accomplish what SELECT INTO does  with SELECT INTO you do not have to know the table definition beforehand  SELECT INTO is probably included in SQL because it makes tasks like ad hoc reporting or copying tables much easier

User · Answer

Each statement has a distinct use case  They are not interchangeable   SELECT   INTO MyTable    creates a new MyTable where one did not exist before    INSERT INTO MyTable   SELECT    is used when MyTable already exists

User · Answer

The other answers are all great correct  the main difference is whether the DestTable exists already  INSERT   or doesn t exist yet  SELECT     INTO   You may prefer to use INSERT  instead of SELECT     INTO   if you want to be able to COUNT    the rows that have been inserted so far  Using SELECT COUNT        WITH NOLOCK is a simple crude technique that may help you check the  quot progress quot  of the INSERT  helpful if it s a long-running insert  as seen in this answer     If you use     INSERT DestTable SELECT     FROM SrcTable    then your SELECT COUNT    from DestTable WITH  NOLOCK  query would work

User · Answer

They do different things   Use INSERT when the table exists   Use SELECT INTO when it does not    Yes   INSERT with no table hints is normally logged   SELECT INTO is minimally logged assuming proper trace flags are set  In my experience SELECT INTO is most commonly used with intermediate data sets  like  temp tables  or to copy out an entire table like for a backup   INSERT INTO is used when you insert into an existing table with a known structure    EDIT  To address your edit  they do different things   If you are making a table and want to define the structure use CREATE TABLE and INSERT   Example of an issue that can be created  You have a small table with a varchar field   The largest string in your table now is 12 bytes   Your real data set will need up to 200 bytes   If you do SELECT INTO from your small table to make a new one  the later INSERT will fail with a truncation error because your fields are too small

User · Answer

Select into for large datasets may be good only for a single user using one single connection to the database doing a bulk operation task  I do not recommend to use   SELECT   INTO table   as this creates one big transaction and creates schema lock to create the object  preventing other users to create object or access system objects until the SELECT INTO operation completes    As proof of concept open 2 sessions  in first session try to use   select into temp table from a huge table    and in the second section try to   create a temp table    and check the locks  blocking and the duration of second session to create a temp table object  My recommendation it is always a good practice to create and Insert statement and if needed for minimal logging use trace flag 610

[sql-server] INSERT INTO vs SELECT INTO

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