ORA-00933 using case/when inside a select - sql

Question

I'm trying to write this code into the toad, but it throws an ORA-00933 (SQL command not properly ended), just at the first WHEN.
I don't know exactly what happens. I've tried to follow the ORACLE docs, but with no success. Any help?
I let you the code written with toad.
select template.seq_temp, rules.fec_desde_serv, rules.seq_rec, rules.seq_agencia, rules.SEQ_TTOO, rules.COD_INTERFACE, pais.COD_PAIS, rules.cod_idioma
from re_t_vp_voucher_template template, re_t_vp_voucher_rules rules, re_t_vp_voucher_rules_pais pais,
case &tipser
when 'TRF' then re_t_vp_voucher_rules_trf trf
when 'ACC' then re_t_vp_voucher_rules_acc acct
else re_t_vp_voucher_rules_otro otro
end
where template.seq_temp = rules.seq_temp
and RULES.SEQ_RULE = PAIS.SEQ_RULE
group by template.seq_temp, rules.fec_desde_serv, rules.seq_rec, rules.seq_agencia, rules.SEQ_TTOO, rules.COD_INTERFACE, pais.COD_PAIS, rules.cod_idioma
order by template.seq_temp, rules.fec_desde_serv;

Answer 1

You cannot use CASE construct in FROM clause.
So your SQL as highlighted below is incorrect.
from re_t_vp_voucher_template template, re_t_vp_voucher_rules rules, re_t_vp_voucher_rules_pais pais,
case &tipser
when 'TRF' then re_t_vp_voucher_rules_trf trf
when 'ACC' then re_t_vp_voucher_rules_acc acct
else re_t_vp_voucher_rules_otro otro
end
where template.seq_temp = rules.seq_temp
The reason is that, you are trying to use dynamic table names in SQL, which is NOT allowed. You can't use dynamic table names in SQL unless you write dynamic SQL statements (i.e. build up the statement as a string in PL/SQL and then execute it using EXECUTE IMMEDIATE or the DBMS_SQL package).
So rewrite the query to meet the SQL standards, or (ab)use dynamic sql.
CASE is an expression, which works like IF-THEN-ELSE logic, and Oracle
uses short-circuit evaluation. so, it always needs a comparison
expression. Which you cannot have in FROM clause.

Answer 2

Your where condition is wrong.:-
where template.seq_temp = rules.seq_temp
and RULES.SEQ_RULE = PAIS.SEQ_RULE
case &tipser
when 'TRF' then and rules.seq_rule = trf.seq_rule
when 'ACC' then and rules.seq_rule = acct.seq_rule
else and rules.seq_rule = otro.seq_rule
end
Try to remove the 'and' keywords from there.