Question

I need some help figuring out the SQL for combining two tables into one table. I’m wanting to combine the tables and display the data on different rows for each table, but what I have below makes only one row.

Here are the tables:

CREATE TABLE tenant_invoices(
  invoice_id INT,
  col1 INT,
  col2 INT
)

CREATE TABLE tenant_payments(
  pmt_invoice_id INT,
  colA INT,
  colB INT
)

Here are the temporary tables I need to create:

CREATE TEMPORARY TABLE tenant_invoices
    SELECT * FROM invoices

CREATE TEMPORARY TABLE tenant_payments
    SELECT * FROM payments

select ti.*, tp.*
from tenant_invoices ti
left join tenant_payments tp
  on ti.invoice_id = tp.pmt_invoice_id
ORDER BY ti.invoice_date DESC;

This results in two tables merge together but only one row is created:

invoice_id   col1   col2    pmt_invoice_id   colA   ColB
1            ABC    XYZ     1                111    222

I’m wanting the table to be able to merge the tables together so I get all the columns, but instead of one row with combined data I want the rows separated so I can loop through the data in a more logical fashion:

invoice_id   col1   col2    pmt_invoice_id   colA   ColB
1            ABC    XYZ     null             null   null
                            1                111    222 

Is there a way I can accomplish this with SQL?

Thanks.

Answer 1

To achieve this result…

invoice_id   col1   col2    pmt_invoice_id   colA   ColB
1            ABC    XYZ     null             null   null
                            1                111    222 

You can use UNION ALL like so:

SELECT invoice_id, col1, col2, NULL AS pmt_invoice_id, NULL AS colA, NULL AS col
FROM tenant_invoices
UNION ALL
SELECT NULL, NULL, NULL, pmt_invoice_id, colA, colB
FROM tenant_payments

As already mentioned, to simply stack the two tables on top of each other, then you align the columns and use UNION ALL. If you wish to remove duplicates, you can use UNION.