Question

I have 2 tables as below, and insert data into ftable from f_table accordingly. I want to insert field_3 into field3 if field_3 exists, else insert field_4 into field3.

How do I do that? Much appreciate for any reply.

CREATE TABLE ftable
(
field1 int null,
field2 int null,
field3 char(1)
);

CREATE TABLE f_table
(
field_1 int null,
field_2 int null,
field_3 char(1),
field_4 char(1)
);

INSERT INTO ftable (field1, field2, field3) 
    SELECT (field_1, field_2, field_3) 
    FROM f_table;

Answer 1

Not sure what you really mean by if field_3 exists – since it’s part of the table, that column always exists…

Guessing that you probably mean: if it’s NOT NULL – in that case, use this CASE statement:

INSERT INTO ftable (field1, field2, field3) 
    SELECT 
       field_1, field_2, 
       CASE
           WHEN field_3 IS NOT NULL THEN field_3
           ELSE field_4
       END
    FROM f_table;

Update: as per w0lf’s suggestion, you could also use:

INSERT INTO ftable (field1, field2, field3) 
    SELECT 
       field_1, field_2, 
       ISNULL(field_3, field_4)
    FROM f_table;

Makes it a bit more compact – but a tad less readable, in my opinion. But this will work just fine – if field_3 is NULL, then field_4 is inserted instead.