sql: fix the handling of sorting, grouping and column ordinals. #10799

knz · 2016-11-19T01:25:53Z

Prior to this patch there was some confusion in the code about how to
interpret the arguments to ORDER BY and GROUP BY clauses.

This patch restores sane behavior:

for sorting:
1. column ordinals. If a simple integer literal is used, optionally
  enclosed within parentheses but not subject to any arithmetic,
  then this refers to one of the columns of the data source. Then
  use the render expression at that ordinal position as sort key.
2. non-integer constant. If ORDER BY is followed by a constant that
  is not a column ordinal, an error is reported.
3. if the expression is the aliased (AS) name of a render expression
  in a SELECT clause, then use that render as sort key.
  e.g. SELECT a AS b, b AS c ORDER BY b this sorts on the first
  render (column a).
4. otherwise, if the expression is already rendered, then use that
  render as sort key. e.g. SELECT b AS c ORDER BY b sorts on the
  first render. (this is a new optimization)
5. if the sort key is not dependent on the data source (no IndexedVar,
  no stars) then simply do not sort. e.g. SELECT * FROM t ORDER BY 3+3
  simplifies to SELECT * FROM t.
  (this is a new optimization)
6. otherwise, add a new render with the ORDER BY expression
  and use that as sort key.
  e.g. SELECT a FROM t ORDER by b
  e.g. SELECT a, b FROM t ORDER by a+b
  But also: SELECT a FROM t ORDER BY t.*
for grouping:
1. column ordinals are detected first thing, like for ORDER BY above.
2. constant expressions are rejected, like for ORDER BY above.

Fixes #10776.

cc @paperstreet @RaduBerinde.

This change is

nvanbenschoten · 2016-11-21T07:02:42Z

Reviewed 18 of 18 files at r1.
Review status: all files reviewed at latest revision, 5 unresolved discussions, some commit checks failed.

pkg/sql/sort.go, line 95 at r1 (raw file):

The logical data source for ORDER BY is the list of render expressions for a SELECT

Doesn't this sentence contradict cases where renders are added when needed by the ORDER BY but not previously present in the render list?

pkg/sql/sort.go, line 96 at r1 (raw file):

		// The logical data source for ORDER BY is the list of render
		// expressions for a SELECT (or an entire UNION or VALUES clause).
		// Alas, SQL has some historical baggage and there is some

s/is some special case/are some special cases/

pkg/sql/sort.go, line 111 at r1 (raw file):

		//    this sorts on the first render.
		//
		// 3) otherwise, if the expression is already rendered,

What do you mean by "already rendered"? Already added to the render list?

pkg/sql/sort.go, line 218 at r1 (raw file):

				// If more than 1 column were expanded, turn them into sort columns too.
				// Except the last one, which will be added below.
				ordering = append(ordering, sqlbase.ColumnOrderInfo{ColIdx: extraIdx, Direction: direction})

long line

pkg/sql/testdata/order_by, line 204 at r1 (raw file):


query error non-integer constant in ORDER BY: 1 \+ 2
SELECT * FROM t ORDER BY 1+2

Isn't this a valid query? Do we want to be breaking compatibility here?

Example:

postgres=# select * from a order by 2.5+1;
 x
---
 1
 3
 4
(3 rows)

postgres=# select * from a order by 2.5;
ERROR:  non-integer constant in ORDER BY
LINE 1: select * from a order by 2.5;
                                 ^

Comments from Reviewable

knz · 2016-11-21T07:50:40Z

Review status: 13 of 18 files reviewed at latest revision, 5 unresolved discussions.

pkg/sql/sort.go, line 95 at r1 (raw file):