l_where = 'campo = ''valor'''.
SELECT lista_campos
INTO loquesea
FROM tabla
WHERE (l_where).
CONSTANTS: c_valor TYPE tabla-campo VALUE 'valor'.
DATA: l_where TYPE string.
l_where = 'campo = c_valor'.
SELECT lista_campos
INTO loquesea
FROM tabla
WHERE (l_where).
CONSTANTS: c_valor TYPE trdir-cnam VALUE 'cnam'.
DATA: l_where TYPE string.
DATA: loquesea.
l_where = 'campo = c_valor'.
SELECT cnam INTO loquesea
FROM trdir
WHERE (l_where).
ENDSELECT.
DATA: l_where TYPE string.
DATA: loquesea.
l_where = 'campo = ''cnam'''.
SELECT cnam INTO loquesea
FROM trdir
WHERE (l_where).
ENDSELECT.