Oracle中查询的优化

Question

Update table from statement. Using subquery. I need write an update statement that used same table.
I used subquery for update multiple columns. My example.

UPDATE  USER_BANCU.REGISTRU_21052016_AE NEW 
        SET  (
             NEW.LIST_COND,
             NEW.LISTA_FOND,
             NEW.GEN_ACT_NE_LIC,
             NEW.GEN_ACT_LIC
             )
           =

         (
    SELECT 
        OLD.LIST_COND,
        OLD.LISTA_FOND,
        OLD.GEN_ACT_NE_LIC,
        OLD.GEN_ACT_LIC
        FROM (
    SELECT 
      VB.IDNO IDNO ,
      trim_vb(VB.LIST_COND)                LIST_COND,
      trim_vb(VB.LISTA_FOND)               LISTA_FOND,
      REPLACE(VB.GEN_ACT_NE_LIC, ' ','' )  GEN_ACT_NE_LIC,  
      REPLACE(VB.GEN_ACT_LIC, ' ','' )     GEN_ACT_LIC    
      FROM   USER_BANCU.REGISTRU_21052016_AE VB
       ) OLD

        WHERE 
            OLD.IDNO=NEW.IDNO 
      )

         WHERE EXISTS (

         SELECT *    
        FROM (
    SELECT 

      VB.IDNO IDNO ,
      trim_vb(VB.LIST_COND)                LIST_COND,
      trim_vb(VB.LISTA_FOND)               LISTA_FOND,
      REPLACE(VB.GEN_ACT_NE_LIC, ' ','' )  GEN_ACT_NE_LIC,  
      REPLACE(VB.GEN_ACT_LIC, ' ','' )     GEN_ACT_LIC

      FROM   USER_BANCU.REGISTRU_21052016_AE VB
       ) OLD


        WHERE 
         OLD.IDNO=NEW.IDNO 
         )

Update table from statement. Using subbquery. Ability to optimize? Is it possible to create a procedure or a cursor in this case?

I have an error when you run a query --ORA-01427: single-row subquery returns more than one row.

Answer 1

It looks like you've massively overcomplicated the update. Since you're updating every single row in the table with values from the same table, I think you're just trying to do:

update user_bancu.registru_21052016_ae
set    list_cond = trim_vb(vb.list_cond),
       lista_fond = trim_vb(vb.lista_fond),
       gen_act_ne_lic = replace(vb.gen_act_ne_lic, ' '),
       gen_act_lic = replace(vb.gen_act_lic, ' ');

NB I removed the '' from the replace parameters because in Oracle, there isn't such a thing as an empty string - it's treated the same as null. And as the default value of the string-to-replace-with parameter is null, you can just remove the parameter altogether.

Also, replacing the above statement with a procedure involving looping round a cursor is likely to be slower. If you have to have a procedure, just use the update statement directly in the procedure.

If you need to speed things up even further, than the above update statement, I suggest you take a look at the trim_vb function calls - if you can move the logic directly into the update statement, then that should speed things up even more (certainly in pre-12c, user defined function calls in DML statements involve context switching between the SQL and PL/SQL engines, which slows things down.).