mysql NULL function
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adj.<Art>zero value; equal to zero; (agreement) has no legal effect; invalid
mysql NULL functionsyntax
Function:If a column in the table is optional, then we can insert new records or update existing records without adding a value to the column. This means that the field will be saved with a NULL value.
Note: NULL values are handled differently than other values. NULL serves as a placeholder for unknown or inapplicable values.
Comments: NULL and 0 cannot be compared; they are not equivalent.
mysql NULL functionexample
//选取在 "Address" 列中带有 NULL 值的记录 SELECT LastName,FirstName,Address FROM Persons WHERE Address IS NULL; //选取在 "Address" 列中不带有 NULL 值的记录 SELECT LastName,FirstName,Address FROM Persons WHERE Address IS NOT NULL;