sql - Find and update non duplicated record based on one of the column -


i want find non duplicated records , update 1 of column.

ex.

col_1 | col_2 | col_3 | col_4 | col_5     | aa    | bb    | 1     |      | ab    | bc    | 2     |     | ac    | bd    | 3     | b     | bb    | cc    | 1     | b     | bb    | cc    | 2     | c     | cc    | dd    | 1     |

my query has group col_1, , want find out not unique record based on col_2 , col3 , update col_5.

basically output should below,

col_1 | col_2 | col_3 | col_4 | col_5     | aa    | bb    | 1     | 1     | ab    | bc    | 2     | 1     | ac    | bd    | 3     | 1 b     | bb    | cc    | 1     | 0 b     | bb    | cc    | 2     | 0 c     | cc    | dd    | 1     | 0

does have idea how can achieve this? large database, performance key factor.

thanks heaps,

there plenty ways it. solution comes postgres have access to, bet working on tsql should have common syntax.

;with cte_1 (     select col_1 some_table group col_1 having count(*) > 1 ), cte_2 (     select col_1 some_table group col_1, col_2, col_3 having count(*) > 1 ), cte_3 (     select cte_1.col_1 cte_1     left join cte_2 on cte_1.col_1 = cte_2.col_1     cte_2.col_1 null ) update some_table set col_5 = 1 cte_3 cte_3.col_1 = some_table.col_1;

so, happens above?

  1. first build 3 cte semi-tables allow split logic smaller parts:

    • cte_1 extracts rows can have multiple col2 , col_3 rows
    • cte_2 selects have non-unique col_2 , col_3
    • cte_3 returns col_1 have unique col_2 , col_3 left join

  2. using last cte_3 structure able update some_table correctly

i assume table called some_table here. if you're worring performance should provide primary key here , have indexes on col_2 , col_3 (standalone may if composite on (col_1, col_2) , on).

also may want move cte use temporary tables (which indexed gain efficiency.

please note query works fine example without real data may guessing. mean happen when have col_1=a unique , non-uniqe col_2 in same time?

but believe it's point start.


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