哈希匹配聚合成本

Question

我正在尝试优化特定查询 我尝试使用哈希表，但性能没有那么大提高 我需要三次加入同一个表 - pratichesteps - 然后最终加入 - pratiche - table 这是查询

SELECT DISTINCT dbo.PRATICHESTEPS.IDPraticaStep AS IDPraticaEsame,
                PRATICHESTEPS_3.IDPraticaStep   AS IDPraticaCatena,
                dbo.PRATICHE.IDSysStato         AS IDStatoCatena,
                dbo.PRATICHE.IDPraticaAccorpata,
                PRATICHESTEPS_3.IDAnalisiStep,
                dbo.PRATICHE.IDTipoAtto,
                PRATICHESTEPS_3.Accorpamento,
                dbo.PRATICHE.DataRegistrazione,
                PRATICHESTEPS_3.LastStep
FROM   dbo.PRATICHESTEPS
       INNER JOIN dbo.PRATICHESTEPS AS PRATICHESTEPS_1
         ON dbo.PRATICHESTEPS.IDPraticaCarico = PRATICHESTEPS_1.IDPraticaCarico
       INNER JOIN dbo.PRATICHESTEPS AS PRATICHESTEPS_2
         ON PRATICHESTEPS_1.IDPraticaStep = PRATICHESTEPS_2.IDPraticaStep
       INNER JOIN dbo.PRATICHESTEPS AS PRATICHESTEPS_3
         ON PRATICHESTEPS_2.IDPraticaCarico = PRATICHESTEPS_3.IDPraticaCarico
       INNER JOIN dbo.PRATICHE
         ON PRATICHESTEPS_3.IDPraticaStep = dbo.PRATICHE.IDPratica