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MySQL 5.5 Reference Manual  /  ...  /  NULL Values

9.1.7 NULL Values

The NULL value means no data. NULL can be written in any lettercase. A synonym is \N (case-sensitive).

Be aware that the NULL value is different from values such as 0 for numeric types or the empty string for string types. For more information, see Section B.5.4.3, “Problems with NULL Values”.

For text file import or export operations performed with LOAD DATA INFILE or SELECT ... INTO OUTFILE, NULL is represented by the \N sequence. See Section 13.2.6, “LOAD DATA INFILE Syntax”.

For sorting with ORDER BY, NULL values sort before other values for ascending sorts, after other values for descending sorts.

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