The difference between Oracle hollow string and null

In Oracle, the empty string is a string of length 0, which means there are no characters; and NULL is a special value, which means a missing or unknown value. Empty strings and NULL have different comparison behavior, function and operator behavior, and storage space usage. An empty string is equal to another empty string when compared, appears as non-empty in functions and operators, and occupies 1 byte of storage space. NULL is not equal to any value during comparison, appears as NULL in functions and operators, and does not occupy storage space.

The difference between empty string and NULL in Oracle

In Oracle database, empty string and NULL are two different things A different concept with different meanings and behaviors.

Concept

• Empty string: A string with a length of 0, indicating no characters.
• NULL: A special value that represents a missing or unknown value.

Behavior

Comparison:

• An empty string is equal to another empty character when compared String, but not equal to NULL.
• NULL is not equal to any value when compared, including itself.

Functions and operators:

• The empty string appears as non-empty in some functions and operators, such as the LENGTH() function and concatenation operator ( ).
• NULL behaves as NULL in most functions and operators.

Storage space:

• The empty string occupies 1 byte of storage space.
• NULL does not occupy storage space.

Other differences:

• Uniqueness: Each empty string is unique, while NULL is a global value.
• Aggregation functions: Empty strings are treated as non-null in aggregate functions, and NULL is ignored.
• Indexing: Empty strings can be indexed, but NULL cannot.

Summary

The empty string represents a string of length 0, while NULL represents a missing or unknown value. They have different behavior in comparisons, functions, and operators, and occupy different storage space.

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