mysql – What does SQL clause “GROUP BY 1” mean?

The Question :

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Someone sent me a SQL query where the GROUP BY clause consisted of the statement: GROUP BY 1.

This must be a typo right? No column is given the alias 1. What could this mean? Am I right to assume that this must be a typo?

The Question Comments :
  • Its not a typo, its the first column of your result set
  • Note that this syntax is non-portable. It will behave differently on databases other than mysql. In Oracle, for instance, it’s treated as a constant.
  • @RussellReed Yes. unfortunately (since using an alias is sometimes very helpful) ansi sql does not allow grouping by column ordinal. The reason is that the group by happens before projection. But then .. what when we have grouping expressions with tens of lines .. we end up with .. mutiples of tens of lines in the final sql statement.

The Answer 1

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It means to group by the first column regardless of what it’s called. You can do the same with ORDER BY.

The Answer 2

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SELECT account_id, open_emp_id
         ^^^^        ^^^^
          1           2

FROM account

In above query GROUP BY 1 refers to the first column in select statement which is account_id.

You also can specify in ORDER BY.

Note : The number in ORDER BY and GROUP BY always start with 1 not with 0.

The Answer 3

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In addition to grouping by the field name, you may also group by ordinal, or position of the field within the table. 1 corresponds to the first field (regardless of name), 2 is the second, and so on.

This is generally ill-advised if you’re grouping on something specific, since the table/view structure may change. Additionally, it may be difficult to quickly comprehend what your SQL query is doing if you haven’t memorized the table fields.

If you are returning a unique set, or quickly performing a temporary lookup, this is nice shorthand syntax to reduce typing. If you plan to run the query again at some point, I’d recommend replacing those to avoid future confusion and unexpected complications (due to scheme changes).

The Answer 4

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It will group by first field in the select clause

The Answer 5

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That means sql group by 1st column in your select clause, we always use this GROUP BY 1 together with ORDER BY 1, besides you can also use like this GROUP BY 1,2,3.., of course it is convenient for us but you need to pay attention to that condition the result may be not what you want if some one has modified your select columns, and it’s not visualized

The Answer 6

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It will group by the column position you put after the group by clause.

for example if you run ‘SELECT SALESMAN_NAME, SUM(SALES) FROM SALES GROUP BY 1‘ it will group by SALESMAN_NAME.

One risk on doing that is if you run ‘Select *‘ and for some reason you recreate the table with columns on a different order, it will give you a different result than you would expect.

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