MySQL Nested Case SQL statements (CASE WHEN OR THEN ELSE END )

Following is an example of nested MySQL Case When or then else End statement.

select
  CASE
  When (table.field1 = '01')
    THEN
      CASE
      When (SUBSTRING_INDEX(table.field1, ' ', 1) = 'abc')
         THEN '01abc'
         ELSE 'abc'
      END
  WHEN (table.field1 = '02')
    THEN
      CASE
      When ((SUBSTRING_INDEX(table.field1, ' ', 1)) = 'def')
        THEN '02def'
        ELSE 'def'
      END
  When (table.field1 = '03')
    THEN
      CASE
      When ((SUBSTRING_INDEX(table.field1, ' ', 1)) = 'efg')
        THEN '03efg'
      ELSE 'efg'
      END
  WHEN (table.field1 = '04')
    THEN
      CASE
      When ((SUBSTRING_INDEX(table.field1, ' ', 1)) = 'pqr')
        THEN '04pqr'
      ELSE 'pqr'
      END
  END
from table ;