Home/ Questions/Q 8520043
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-11T06:25:28+00:00

Example scenario: TABLE_A contains a column called ID and also contains duplicate rows. There

  • 0

Example scenario:

TABLE_A contains a column called ID and also contains duplicate rows. There is another table called ID_TABLE that contains IDs. Assuming no duplicates in ID_TABLE –

If I do:

SELECT * FROM TABLE_A
INNER JOIN ID_TABLE ON ID_TABLE.ID = TABLE_A.ID

There will be duplicates in the result set. However, if I do:

SELECT * FROM TABLE_A
WHERE TABLE_A.ID IN (SELECT ID_TABLE.ID FROM ID_TABLE)

There will not be any duplicates in the result set.

Does anyone know why the JOIN clause allows duplicates while the IN clause does not? I had thought they did the same thing.

Thanks

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    It’s not that it’s allowing duplicates. By joining the two tables, you are creating a product from table 1 and table 2, so if TABLE_A has two records for ID=1 and ID_Table has 1 record, the resulting product is two records. Using IN doesn’t cause a multiplication of records, even if the value is listed in the IN clause multiple times as you are only getting the unique records matching the values within the IN clause.

    • 0