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Can I insert an empty string in a not null field?
insert into xyz(A,B) values(1,''); // is this possible if B is NOT NULL?
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An empty string is a string instance of zero length, whereas a null string has no value at all. An empty string is represented as "" . It is a character sequence of zero characters.
An empty string is useful when the data comes from multiple resources. NULL is used when some fields are optional, and the data is unknown.
You also can specify the NULL keyword in the VALUES clause to indicate that a column should be assigned a NULL value. The following example inserts values into three columns of the orders table: INSERT INTO orders (orders_num, order_date, customer_num) VALUES (0, NULL, 123);
NULL is used in SQL to indicate that a value doesn't exist in the database. It's not to be confused with an empty string or a zero value. While NULL indicates the absence of a value, the empty string and zero both represent actual values.
Yes you can... The concept of the NULL value is a common source of confusion for newcomers to SQL, who often think that NULL is the same as an empty string '', or a value of zero.
This is not the case. Conceptually, NULL means "a missing unknown value" and it is treated somewhat differently from other values. For example, to test for NULL, you cannot use the arithmetic comparison operators such as =, <, or <> in most DBMSes.
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