
Explanation:
The NCHAR(10) data type is a fixed-length Unicode character data type. Each character in NCHAR takes 2 bytes because it uses UTF-16 encoding. Therefore, NCHAR(10) will always occupy 20 bytes on disk (2 bytes per character for 10 characters), not 10 bytes. However, the statement is asking if each field occupies 10 bytes, which is misleading; it should be 20 bytes.
The statement "ALTER TABLE table1 REBUILD WITH (DATA_COMPRESSION = ROW);" specifies row-level compression, not dictionary compression. Row compression reduces the size of the data by storing fixed-length data types in variable-length storage format and by reducing metadata overhead. Dictionary compression is a feature of page compression, not row compression.
Column1 (TINYINT): Supports compression. Row compression can store this as a smaller size if possible. Column2 (VARCHAR(255)): Supports compression. Row compression can store only the used length of the string. Column4 (BINARY(50)): Supports compression. Row compression can store binary data more efficiently by removing unnecessary padding.