Question

I have a statement that looks something like this:

insert table_name(...)
select .... from ... join ... 

How can I use where not exists or something of that effect with this insert and select statement so that if this exact code is reran with the same values, it won’t throw an error. I don’t want to have to copy and paste the select/joins in a check as it is a pretty big block of code, so is there any way to do something like

if not exists (insert table_name(...)
              select ... from...join)

or would it be something else like

insert table_name(...)
if not exists(select ... from ... join)

Answer 1

Trying to keep this as generic as you did and still have it make sense. Hopefully, this is understandable.

insert table_name(...)
select .... from ... join ... 
WHERE NOT EXISTS(SELECT NULL 
                     FROM table_name
                     WHERE PKColumn = YourOuterSelectTable.PKColumn)

To try to put some more meat on it:

/* Assume Column1 is primary key */
INSERT INTO table_name
    (Column1, Column2)
    SELECT a.Column1, b.Column2
        FROM TableA a
            INNER JOIN TableB b
                ON a.Column1 = b.FKColumn1
        WHERE NOT EXISTS (SELECT NULL
                              FROM table_name
                              WHERE Column1 = a.Column1)