Rows from different tables in one row sql

Question

I'm searching for a solution to combine 3 select query's in 1 query to optimize the speed of our product with reducing waiting time from the database. This is the situation:

There are 3 tables

the first table (employer):

*ID  username*
1   employerFirst
2   employerSecond
3   omployerThird

second table (employee):

*ID  username*
1   employeeFirst
2   employeeSecond
3   employeeThird

last table (third part):

*ID  username*
1   partFirst
2   partSecond
3   partThird

What I need:

*username*
employerFirst
employerSecond
employerThird
employeeFirst
employeeSecond
employeeThird
partFirst
partSecond
partThird

Answer 1

Use UNION ALL or UNION.

UNION removes duplicates, while UNION ALL will keep duplicate values.
Depends on what you're approaching.

    SELECT username FROM employer
 UNION ALL
    SELECT username FROM employee
 UNION ALL
    SELECT username FROM third_Part

or if you don't want to return duplicate values:

    SELECT username FROM employer
     UNION 
    SELECT username FROM employee
     UNION 
    SELECT username FROM third_Part