CASE .. WHEN expression in Oracle SQL

Question

I have the table with 1 column and has following data

Status
a1
i
t
a2
a3

I want to display the following result in my select query

Answer 1

CASE TO_CHAR(META.RHCONTRATOSFOLHA.CONTRATO)
WHEN '91' AND TO_CHAR(META.RHCONTRATOSFOLHA.UNIDADE) = '0001' THEN '91RJ'
WHEN '91' AND TO_CHAR(META.RHCONTRATOSFOLHA.UNIDADE) = '0002' THEN '91SP'
END CONTRATO,

00905. 00000 -  "missing keyword"
*Cause:    
*Action:
Erro na linha: 15 Coluna: 11