distsql: fix EXPLAIN(DISTSQL) ignoring subqueries

[asubiotto]

Fixes #25610

Release note: None

[cockroach-teamcity]

This change is 

[RaduBerinde]

I'd add in the comment or release note how the behavior is changed

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Review status: 0 of 1 files reviewed at latest revision, all discussions resolved.

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pkg/sql/explain_distsql.go, line 58 at r1 (raw file):

	}

	auto = ok && auto

The semantics of EXPLAIN (DISTSQL) are that it errors out on unsupported queries. Otherwise the implication is that you can still run them in ON mode.

We can add a flag to prepareForDistSQLSupportCheck for this behavior (and pass p.SessionData().DistSQLMode == sessiondata.DistSQLAlways as the value for the flag in the existing path)

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Comments from Reviewable

[asubiotto]

Review status: 0 of 1 files reviewed at latest revision, 1 unresolved discussion, some commit checks failed.

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pkg/sql/explain_distsql.go, line 58 at r1 (raw file):

Previously, RaduBerinde wrote…

The semantics of EXPLAIN (DISTSQL) are that it errors out on unsupported queries. Otherwise the implication is that you can still run them in ON mode.

We can add a flag to prepareForDistSQLSupportCheck for this behavior (and pass p.SessionData().DistSQLMode == sessiondata.DistSQLAlways as the value for the flag in the existing path)

Done.

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Comments from Reviewable

[RaduBerinde]

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Review status: 0 of 4 files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[asubiotto]

TFTR!
bors r+

[craig]

Build succeeded

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