colfetcher: fix NULL checks during unique index decoding

[mgartner]

colfetcher must detect NULL values in unique secondary index keys on
tables with multiple column families in order to determine whether
consecutive KVs belongs to the same row or different rows. Previously,
only the columns in the key that were needed by the query were decoded
and checked for NULL. This caused incorrect query results when NULL
column values were not detected because those columns were not needed.

This commit fixes the issue by checking all columns for NULL when
decoding unique secondary index keys on tables with multiple column
families.

Fixes #66706

Release note (bug fix): A bug has been fix that caused incorrect query
results when querying tables with multiple column families and unique
secondary indexes. The bug only occurred if 1) vectorized execution was
enabled for the query, 2) the query scanned a unique secondary index
that contained columns from more than one column family, and 3) rows
fetched by the query contained NULL values for some of the indexed
columns. This bug was present since version 20.1.

[cockroach-teamcity]

This change is 

[cucaroach]

Reviewed 3 of 3 files at r1.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @michae2 and @yuzefovich)

[cucaroach]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @michae2 and @yuzefovich)

[yuzefovich]

Reviewed 3 of 3 files at r1.
Reviewable status: complete! 2 of 0 LGTMs obtained (waiting on @mgartner and @michae2)

---

pkg/sql/colencoding/key_encoding.go, line 184 at r1 (raw file):

		if i == -1 {
			if checkAllColsForNull {
				_, isNull := encoding.DecodeIfNull(key)

super nit: this could be simplified into isNull := encoding.PeekType(key) == encoding.Null.

---

pkg/sql/logictest/testdata/logic_test/vectorize, line 1256 at r1 (raw file):

# consecutive KVs in a unique secondary index belong to the same row.
statement ok
SET vectorize=on

This is not needed - in this file we execute almost all queries with vectorize=experimental_always.

[mgartner]

Reviewable status: complete! 0 of 0 LGTMs obtained (and 2 stale) (waiting on @cucaroach, @michae2, and @yuzefovich)

---

pkg/sql/colencoding/key_encoding.go, line 184 at r1 (raw file):

Previously, yuzefovich (Yahor Yuzefovich) wrote…

super nit: this could be simplified into isNull := encoding.PeekType(key) == encoding.Null.

Done.

---

pkg/sql/logictest/testdata/logic_test/vectorize, line 1256 at r1 (raw file):

Previously, yuzefovich (Yahor Yuzefovich) wrote…

This is not needed - in this file we execute almost all queries with vectorize=experimental_always.

Done.

[michae2]

Reviewable status: complete! 1 of 0 LGTMs obtained (and 2 stale) (waiting on @cucaroach and @yuzefovich)

[mgartner]

TFTRs!

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)

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