mysql union different number of columns

Question

I know union queries have to have the same number of columns. I\'m trying to get results from the table comments and results from the table strings

Answer 1

Add empty columns (null as columnName) to the query that has fewer columns. You should avoid using * in this case, to have better control on order of columns in both queries.

Answer 2

You would want to select columns as NULL to take up for the empty space in certain tables.

Table A: (id, column1)

Table B: (id, column1, column2)

Select id, column1, null as column2 from tableA
UNION
Select id, column1, column2 from tableB

Answer 3

Another very dodgy way to get around the issue is to CONCAT_WS columns not shared between the tables e.g.

SELECT `r_id`, `r_added`, CONCAT_WS('###',`otherfield1`,`otherfield2`) as r_other FROM table1
UNION
SELECT `r_id`, `r_added`, CONCAT_WS('###',`otherfield3`,`otherfield4`,`otherfield5`) as r_other FROM table2

You can then programmatically reconstruct that data e.g.

$rother = explode("###", $row['r_other']);

Very bad way to get at this data but might get someone out of a fix. You could even change the separator e.g. #t1# #t2# search the string for that to workout what table the concatenated data is from.