planner: fix incorrect table name in explain information

[foreyes]

What problem does this PR solve?

Fix #11782

What is changed and how it works?

Add necessary TableAsName field into PhysicalTableScan.
For case 1, add it in constructInnerIndexScanTask.
For case 2, add it in convertToIndexScan.

For case 3, this case happens because we set TableAsName after buildDataSource. In most cases it goes well, but when we need union scan, line 2348 will be triggered:

if txn.Valid() && !txn.IsReadOnly() && !isMemDB {
	us := LogicalUnionScan{handleCol: handleCol}.Init(b.ctx)
	us.SetChildren(ds)
	result = us
}

The return value is LogicalUnionScan instead of DataSource, so TableAsName will not be set in these lines of buildResultSetNode:

if v, ok := p.(*DataSource); ok {
	v.TableAsName = &x.AsName
}

So we can pass &x.AsName into buildDataSource, and set TableAsName in it.

Check List

Tests

• Unit test
• Explain test

Side effects

• Change explain information in some cases.

[codecov]

Codecov Report

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[foreyes]

/run-all-tests

[foreyes]

/run-unit-test

[foreyes]

/run-all-tests

[winoros]

lgtm

[lzmhhh123]

LGTM.

[sre-bot]

/run-all-tests