It's a bad idea to mix SQL-89 (joining through using commas) and SQL-92
(using join) syntax, and I'm not used to using GROUP BY on fields used
in a calculation (although this may well be legal). And why do you use
LEFT JOIN TM when you refer to it in the WHERE clause as if it was an
INNER JOIN? Moreover, I do not understand why you use GROUP BY at all in
your query since you do not use any aggregated functions - using SELECT
DISTINCT should be a simpler way to achieve the same result.

Here's an attempt to rewrite your view, it may differ slightly from your
original query since it will not return duplicates if two of the UNION
ALLs in your original query could be identical:

CREATE OR ALTER VIEW ESPELHO12(
CODEMPRESA, CODFILIAL, DTMOVPROD, CODMOVIMENTO, CODPRODUTO,
TIPOMOVIMENTO, QUANTIDADE, SALDO, CFOP, CODCOMPRA,
CODVENDA, DESCRICAO, NCM, DOCUMENTO, TIPOPRODUTO,
CUSTO, TMEMPRESA, TMFILIAL, NOMERAZAOTIPO )
AS
SELECT MP.CODEMP, MP.CODFILIAL, MP.DTMOVPROD, MP.CODMOVPROD,
MP.CODPROD,
MP.CODTIPOMOV, MP.QTDMOVPROD, MP.SLDMOVPROD, MP.CODNAT,
MP.CODCOMPRA,
MP.CODVENDA, EQ.DESCPROD, EQ.CODFISC, MP.DOCMOVPROD,
EQ.TIPOPROD,
CAST((MP.sldmovprod*EQ.CUSTOINFOPROD) AS NUMERIC(15,2)) CUSTO,
TM.CODEMP AS TMEMP, TM.CODFILIAL AS TMFIL, TM.DESCTIPOMOV
FROM EQMOVPROD MP
INNER JOIN EQPRODUTO eq on mp.codprod = eq.codprod
INNER JOIN eqtipomov tm on tm.codtipomov = mp.codtipomov
AND TM.CODEMP = MP.CODEMP
AND TM.CODFILIAL = MP.CODFILIAL
AND TM.CODTIPOMOV = MP.CODTIPOMOV
where EQ.tipoprod='P'
and mp.codvenda is null
and mp.codcompra is null
UNION
SELECT MP.CODEMP, MP.CODFILIAL, MP.DTMOVPROD, MP.CODMOVPROD,
MP.CODPROD,
MP.CODTIPOMOV, MP.QTDMOVPROD, MP.SLDMOVPROD, MP.CODNAT,
MP.CODCOMPRA,
MP.CODVENDA, EQ.DESCPROD, EQ.CODFISC, MP.DOCMOVPROD,
EQ.TIPOPROD,
CAST((MP.sldmovprod*EQ.CUSTOINFOPROD) AS NUMERIC(15,2)) CUSTO,
TM.CODEMP AS TMEMP, TM.CODFILIAL AS TMFIL, FORN.RAZFOR AS NOMEFORNECEDOR
FROM EQMOVPROD MP
INNER JOIN EQTIPOMOV TM ON MP.CODEMP=TM.CODEMP
AND MP.CODFILIAL=TM.CODFILIAL
AND MP.CODTIPOMOV=TM.CODTIPOMOV
INNER JOIN EQPRODUTO eq on mp.codprod = eq.codprod
LEFT JOIN cpcompra cp on mp.codcompra = cp.codcompra
LEFT JOIN cpforneced forn on cp.codfor =forn.codfor
where EQ.tipoprod='P'
and mp.codvenda is null
and mp.codcompra is not null
UNION
SELECT MP.CODEMP, MP.CODFILIAL, MP.DTMOVPROD, MP.CODMOVPROD,
MP.CODPROD,
MP.CODTIPOMOV, mP.QTDMOVPROD, MP.SLDMOVPROD, MP.CODNAT,
MP.CODCOMPRA,
MP.CODVENDA, EQ.DESCPROD, EQ.CODFISC, MP.DOCMOVPROD,
EQ.TIPOPROD,
CAST((MP.sldmovprod*EQ.CUSTOINFOPROD) AS NUMERIC(15,2)),
TM.CODEMP, TM.CODFILIAL, cast(CLI.NOMECLI as char(60))
FROM EQMOVPROD MP
INNER JOIN EQTIPOMOV TM ON MP.CODEMP=TM.CODEMP
AND MP.CODFILIAL=TM.CODFILIAL
AND MP.CODTIPOMOV=TM.CODTIPOMOV
INNER JOIN EQPRODUTO eq on mp.codprod = eq.codprod
LEFT join vdvenda vd on mp.codvenda=vd.codvenda
LEFT join vdcliente cli on vd.codcli = cli.codcli
where EQ.tipoprod='P'
and mp.codcompra is null
and mp.codvenda is not null

HTH,
Set