Convert all the data of table (which have both encoding data) into single encoding either utf8 or latin1
Depending on what RDBMS you are using:


You can try altering the Latin1-encoded column to use an encoding of UTF-8, if the RDBMS supports such an operation.

If you are using MySQL, you should look at this related Question on S.O.:
Converting mysql tables from latin1 to utf8
You can try:


Adding a new column with an encoding of UTF-8
UPDATE new_column = Latin1_column  (I am assuming that the RDBMS would be able to implicitly convert since it knows both encodings)
DROP Latin1_column
rename new_column to be former Latin1_column's name