MySql SELECT union for different columns? [duplicate]

Answer 1

If select A does not have a column, simply use a null value

table A (colA, ColB, ColC)

table B (colA, ColD, ColE)

select colA, ColB, ColC, null, null from table A
union
select colA, null, null, colD, colE from table B

just need to be sure that each column you are matching are of the same data type

Answer 2

You can fake a column to do union

eg.

   select x, y from A
     union 
   select z, null from B

Answer 3

If you have different fields that have different meaning too, you can't and shouldn't return them in the same position. You can however 'fill in the blanks' by adding null to your fields, like this:

select id, name, date, null as userid, 'A' as recordtype from table1
union all
select id, name, null /*as date*/, userid, 'B' as recordtype from table2 

You can provide an alias for the null in the first select. You can add aliases in the second select for clarity, but it won't be used. You can even use constant values which you can use to distinguish the record type later.