sql - Similar queries to create third column in MySQL using JOIN -

using question, i've been trying experiment using different types of joins try combine these 2 select queries. similar , work fine when try create third column empfirstname3 query blows up. how combine these 2 tables?

htg_techprops table

empnumber     |     empfirstname  111           |     bob  222           |     john  333           |     randy 

htg_techstaffsets table

empnumber     |     staffsetid  ccn31         |     111  ccn11         |     222  poww          |     null 

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/* techs */     select          p.empnumber,         p.empfirstname empfirstname1,               t.empfirstname empfirstname2     htg_techprops p      left join htg_techstaffsets s on p.empnumber=s.empnumber     left join htg_techprops t on t.empnumber=s.staffsetid     order p.empnumber   /* staff sets */   select      p.empnumber,     p.empfirstname empfirstname1,           t.empfirstname empfirstname2 htg_techprops p  left join htg_techstaffsets s on p.empnumber=s.staffsetid left join htg_techprops t on t.empnumber=s.empnumber order p.empnumber 

try this:

    select          p.empnumber,         p.empfirstname empfirstname1,               t.empfirstname empfirstname2     htg_techprops p      left join htg_techstaffsets s on p.empnumber=s.empnumber     left join htg_techprops t on t.empnumber=s.staffsetid  union  select      p.empnumber,     p.empfirstname empfirstname1,           t.empfirstname empfirstname2 htg_techprops p  left join htg_techstaffsets s on p.empnumber=s.staffsetid left join htg_techprops t on t.empnumber=s.empnumber  order p.empnumber