ddl: Fix NULL value in non-nullable column (#8722)

[ti-chi-bot]

This is an automated cherry-pick of #8722

What problem does this PR solve?

Issue Number: close #8419

Problem Summary: As the issue described. #8419 (comment)

When the column is defined with default value, the column id exists in non-nullable-column-ids:
https://github.com/pingcap/tidb/blob/90fc8148a29ee77708628b6c6984d51b7e9f8cc3/pkg/table/tables/tables.go#L525-L528

There is a function for fixing similar cases, but it only handle the case for "missing column". And those column defined with default value is not consider as "missing column"

tiflash/dbms/src/TiDB/Decode/RowCodec.cpp

Lines 387 to 423 in 752a280

	inline bool addDefaultValueToColumnIfPossible(
	const ColumnInfo & column_info,
	Block & block,
	size_t block_column_pos,
	bool ignore_pk_if_absent,
	bool force_decode)
	{
	// We consider a missing column could be safely filled with NULL, unless it has not default value and is NOT NULL.
	// This could saves lots of unnecessary schema syncs for old data with a newer schema that has newly added columns.
	if (column_info.hasPriKeyFlag())
	{
	// For clustered index or pk_is_handle, if the pk column does not exists, it can still be decoded from the key
	if (ignore_pk_if_absent)
	return true;
	assert(!ignore_pk_if_absent);
	if (!force_decode)
	return false;
	// Else non-clustered index, and not pk_is_handle, it could be a row encoded by older schema,
	// we need to fill the column wich has primary key flag with default value.
	// fallthrough to fill default value when force_decode
	}
	if (column_info.hasNoDefaultValueFlag() && column_info.hasNotNullFlag())
	{
	if (!force_decode)
	return false;
	// Else the row does not contain this "not null" / "no default value" column,
	// it could be a row encoded by older schema.
	// fallthrough to fill default value when force_decode
	}
	// not null or has no default value, tidb will fill with specific value.
	auto * raw_column = const_cast<IColumn *>((block.getByPosition(block_column_pos)).column.get());
	raw_column->insert(column_info.defaultValueToField());
	return true;
	}

What is changed and how it works?

When tiflash meets such NULL datum value in non-nullable column when force_decode==true, just fill with the default value.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Fix the issue that executing the `ALTER TABLE ... MODIFY COLUMN ... NOT NULL` that turn a nullable column to not nullable cause panic

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JaySon-Huang, Lloyd-Pottiger

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• OWNERS [JaySon-Huang,Lloyd-Pottiger]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-01-31 08:12:31.741126283 +0000 UTC m=+1553193.305423984: ☑️ agreed by JaySon-Huang.
• 2024-01-31 08:38:37.128038661 +0000 UTC m=+1554758.692336366: ☑️ agreed by Lloyd-Pottiger.

[JaySon-Huang]

/run-all-tests