Q:

Combining two table without duplicates 

I have a table containing symbols:
Table1 
'sym'
Ibm
Msft
SUnw

Table 2 
'sym'
ABC
BCD
CDE
IBM

Using mysql: how could add the unique 'sym' from table 2 into table 1.

A:

You could use distinct, and add a not exists condition to filter out the symbols already in Table1:
insert  Table1
        (sym)
select  distinct sym
from    Table2
where   not exists
        (
        select  *
        from    Table1
        where   sym = Table2.sym
        )

