Sql Bigquery - 将两列连接成一个新列

Question

I want to concat two columns shown below into one new column.

I'm using this query:

SELECT
CONCAT( A_Bill_ID , ' ', B_BILL_ID ) AS BILL_ID
FROM
`table.tmp_140222`

From this query, the result will be like this.

My problem is I want to concat only columns that don't have a similar value so that the new column value will not duplicate two times. From the above result, the ID is duplicated since both of the columns has the same value.

Can anyone help me?

Thanks

Answer 1

select if (
    a_bill_id = b_bill_id, 
    a_bill_id, 
    concat(a_bill_id , ' ', b_bill_id )
  ) as bill_id
from your_table    

... shows null value....

select if (
    a_bill_id = b_bill_id or (a_bill_id = b_bill_id) is null,
    coalesce(a_bill_id, b_bill_id),
    concat(a_bill_id , ' ', b_bill_id )
  ) as bill_id
from your_table

Answer 2

You can use a case statement like this -

SELECT
case when A_Bill_ID = B_BILL_ID then a_bill_Id 
else CONCAT(A_Bill_ID , ' ', B_BILL_ID ) 
end AS BILL_ID
FROM `table.tmp_140222`

If there are Null values in the initial columns, you can use IFNULL or COALEASE to replace that with an empty string. But in this case, I would suggest using this without a delimiter or writing multiple 'when' statements to avoid tailing spaces in the final column -

SELECT
case when A_Bill_ID = B_BILL_ID then a_bill_Id 
else CONCAT(IFNULL(A_Bill_ID), ''), "", IFNULL(B_BILL_ID, ''))
end AS BILL_ID
FROM `table.tmp_140222`