如何根据最新数据合并多个不同数据的SQL表，并在新数据为空的情况下保留旧数据？

MERGE INTO TargetTable AS target
USING (
    SELECT Column1, Column2, ..., ColumnN
    FROM SourceTable1
    UNION ALL
    SELECT Column1, Column2, ..., ColumnN
    FROM SourceTable2
    -- 可以继续添加更多的源表
) AS source
ON target.PrimaryKey = source.PrimaryKey
WHEN MATCHED AND (source.NewDataColumn IS NOT NULL OR target.OldDataColumn IS NULL)
    THEN UPDATE SET target.Column1 = source.Column1, target.Column2 = source.Column2, ..., target.NewDataColumn = source.NewDataColumn
WHEN NOT MATCHED BY TARGET
    THEN INSERT (PrimaryKey, Column1, Column2, ..., OldDataColumn)
         VALUES (source.PrimaryKey, source.Column1, source.Column2, ..., source.NewDataColumn);

UPDATE TargetTable
SET Column1 = COALESCE(SourceTable1.Column1, TargetTable.Column1),
    Column2 = COALESCE(SourceTable1.Column2, TargetTable.Column2),
    ...,
    NewDataColumn = COALESCE(SourceTable1.NewDataColumn, TargetTable.OldDataColumn)
FROM TargetTable
LEFT JOIN SourceTable1 ON TargetTable.PrimaryKey = SourceTable1.PrimaryKey
UNION ALL
UPDATE TargetTable
SET Column1 = COALESCE(SourceTable2.Column1, TargetTable.Column1),
    Column2 = COALESCE(SourceTable2.Column2, TargetTable.Column2),
    ...,
    NewDataColumn = COALESCE(SourceTable2.NewDataColumn, TargetTable.OldDataColumn)
FROM TargetTable
LEFT JOIN SourceTable2 ON TargetTable.PrimaryKey = SourceTable2.PrimaryKey;