Sql-server – rely on the order of columns on an index generated by database tuning advisor

index-tuningsql-server-2008-r2

I got the following recommendation on a table:

CREATE NONCLUSTERED INDEX 
    [_dta_index_MyTable_6_44943632__K16_K52_K8_K9_K15_1_2_4_5_6_7_10_11_12_13_14_17_18_19_20_21_22_23_24_25_26_27_28_29_30_31_] 
ON [dbo].[MyTable] 
(
    [ColumnA] ASC,
    [ColumnB] ASC,
    [ColumnC] ASC
)

However, I am a bit surprised about the order of the columns in the recommendation. I would expect the result to be ColumnB, ColumnA, ColumnC.

Can I rely on the recommendation or should I decide the order of the columns?

Best Answer

You need to provide more info, specifically why do you expect the order you expect. An index on (A, B, C) is completely different from an index on (B, A, C) and one cannot replace the other. The DTA may be wrong sometimes, but is way more often right rather than wrong.

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