SQL WHERE ID IN id1 id2 idn

Question

I need to write a query to retrieve a big list of ids  We do support many backends  MySQL  Firebird  SQLServer  Oracle  PostgreSQL      so I need to write a standard SQL  The size of the id set could be big  the query would be generated programmatically  So  what is the best approach  1  Writing a query using IN SELECT   FROM TABLE WHERE ID IN  id1  id2       idn   My question here is  What happens if n is very big  Also  what about performance  2  Writing a query using OR SELECT   FROM TABLE WHERE ID   id1 OR ID   id2 OR     OR ID   idn  I think that this approach does not have n limit  but what about performance if n is very big  3  Writing a programmatic solution    foreach  var id in myIdList            var item   GetItemByQuery  quot SELECT   FROM TABLE WHERE ID    quot    id         myObjectList Add item        We experienced some problems with this approach when the database server is queried over the network  Normally is better to do one query that retrieve all results versus making a lot of small queries  Maybe I m wrong  What would be a correct solution for this problem

User · Accepted Answer

Option 1 is the only good solution   Why    Option 2 does the same but you repeat the column name lots of times  additionally the SQL engine doesn t immediately know that you want to check if the value is one of the values in a fixed list  However  a good SQL engine could optimize it to have equal performance like with IN  There s still the readability issue though    Option 3 is simply horrible performance-wise  It sends a query every loop and hammers the database with small queries  It also prevents it from using any optimizations for  value is one of those in a given list

User · Answer

In most database systems  IN  val1  val2       and a series of OR are optimized to the same plan   The third way would be importing the list of values into a temporary table and join it which is more efficient in most systems  if there are lots of values   You may want to read this articles    Passing parameters in MySQL  IN list vs  temporary table

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Doing the SELECT   FROM MyTable where id in    command on an Azure SQL table with 500 million records resulted in a wait time of   7min   Doing this instead returned results immediately   select b id  a   from MyTable a join  values  250000    2500001    2600000   as b id  ON a id   b id   Use a join

User · Answer

Try this SELECT Position ID   Position Name FROM  position WHERE Position ID IN  6  7  8  ORDER BY Position Name

User · Answer

First option is definitely the best option   SELECT   FROM TABLE WHERE ID IN  id1  id2       idn    However considering that the list of ids is very huge  say millions  you should consider chunk sizes like below    Divide you list of Ids into chunks of fixed number  say 100 Chunk size should be decided based upon the memory size of your server Suppose you have 10000 Ids  you will have 10000 100   100 chunks Process one chunk at a time resulting in 100 database calls for select   Why should you divide into chunks      You will never get memory overflow exception which is very common in scenarios like yours    You will have optimized number of database calls resulting in better performance    It has always worked like charm for me  Hope it would work for my fellow developers as well

User · Answer

An alternative approach might be to use another table to contain id values  This other table can then be inner joined on your TABLE to constrain returned rows  This will have the major advantage that you won t need dynamic SQL  problematic at the best of times   and you won t have an infinitely long IN clause     You would truncate this other table  insert your large number of rows  then perhaps create an index to aid the join performance  It would also let you detach the accumulation of these rows from the retrieval of data  perhaps giving you more options to tune performance   Update  Although you could use a temporary table  I did not mean to imply that you must or even should  A permanent table used for temporary data is a common solution with merits beyond that described here

User · Answer

What Ed Guiness suggested is really a performance booster   I had a query like this  select   from table where id in  id1 id2         long list    what i did    DECLARE  temp table              ID  int               insert into  temp  select   from dbo fnSplitter   idlist      Then inner joined the temp with main table    select   from table inner join temp on temp id   table id   And performance improved drastically

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Sample 3 would be the worst performer out of them all because you are hitting up the database countless times for no apparent reason   Loading the data into a temp table and then joining on that would be by far the fastest   After that the IN should work slightly faster than the group of ORs

User · Answer

I think you mean SqlServer but on Oracle you have a hard limit how many IN elements you can specify  1000

[sql] SQL WHERE ID IN (id1, id2, ..., idn)

Why?

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