Localice la posición del texto, extraiga el texto e insértelo en una nueva columna en MySQL

Puede elegir el texto que sigue al 'País=' y luego, una vez que tenga esa subcadena, elegir el texto antes del primer '&'

SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(ColumnA, 'Country=', -1), '&', 1) AS ColumnB
FROM `atable`

Consulte http://dev.mysql. com/doc/refman/5.6/en/string-functions.html#function_substring-index

Aquí hay una prueba para demostrarlo:

mysql> SELECT * FROM atable;
+------+------------------------------------------+
| row  | columna                                  |
+------+------------------------------------------+
| Row1 | Lauguage=English&Country=USA&Gender=Male |
| Row2 | Gender=Female&Language=French&Country=   |
| Row3 | Country=Canada&Gender=&Language=English  |
+------+------------------------------------------+

mysql> SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(ColumnA, 'Country=', -1), '&', 1) AS ColumnB FROM atable;
+---------+
| ColumnB |
+---------+
| USA     |
|         |
| Canada  |
+---------+

Re su pregunta de seguimiento:

INSERT INTO atable VALUES ('Row4', 'Gender=&Language=English');

SELECT `row`, IF(LOCATE('Country=', ColumnA)>0, 
  COALESCE(
    NULLIF(SUBSTRING_INDEX(SUBSTRING_INDEX(ColumnA, 'Country=', -1), '&', 1), ''), 
    'Blank string is not valid!'), 
 'Missing Country!') AS ColumnB     
FROM `atable`

+------+----------------------------+
| row  | ColumnB                    |
+------+----------------------------+
| Row1 | USA                        |
| Row2 | Blank string is not valid! |
| Row3 | Canada                     |
| Row4 | Missing Country!           |
+------+----------------------------+