what is the difference between null and empty in mysql?
537322
NULL is an absence of a value. An empty string is a value, but is just empty. ... NULL isn't allocated any memory, the string with NULL value is just a pointer which is pointing to nowhere in memory. however, Empty IS allocated to a memory location, although the value stored in the memory is "" .
1470928
UPDATE test SET test1 = NVL(test1, 'hello'), test2 = NVL(test2, 'world') WHERE test2 IS NULL OR test1 IS NULL; Though it may fire your update triggers even for the rows that are effectively unchanged. COALESCE() works similarly to NVL() in this circumstance -- returning the first non-null value.
1464470
empty() This function checks whether a variable evaluates to what PHP sees as a "falsy"(a.k.a empty) value. This being said, a variable is empty if it's undefined, null, false, 0 or an empty string.
908555
In C#, IsNullOrEmpty() is a string method. It is used to check whether the specified string is null or an Empty string. A string will be null if it has not been assigned a value. A string will be empty if it is assigned “” or String.
300656
An empty string, however, is a value - it is a string of no characters. Null is essentially 'nothing' - it's the default 'value' (to use the term loosely) that Java assigns to any Object variable that was not initialized. Null isn't really a value - and as such, doesn't have properties.
741522
The NOT NULL constraint is a column constraint that ensures values stored in a column are not NULL . ... A column may contain only one NOT NULL constraint which specifies a rule that the column must not contain any NULL value. In other words, if you update or insert NULL into a NOT NULL column, MySQL will issue an error.
700778
NULL and nil are equal to each other, but nil is an object value while NULL is a generic pointer value ( (void*)0 , to be specific). [NSNull null] is an object that's meant to stand in for nil in situations where nil isn't allowed. For example, you can't have a nil value in an NSArray.
940763
Primary key does not allow NULL values, but unique key allows NULL values. ... You can have more than 1 unique key table column (unlike primary key which means only 1 table column in the table is unique). INDEX also creates uniqueness. MySQL (example) will create a indexing table for the column that is indexed.
102763
If a variable is accessed before defining then JS will show it as not defined, and if a variables is defined but not initialized I.e. no values is assigned it to it before accessing, then its undefined. Null means an empty or non-existent value. Null is assigned, and explicitly means nothing.
1323404
NOT NULL means that the column can not have a NULL value for any record; NULL means NULL is an allowable value (even when the column has a foreign key constraint). ... Generally you want as many columns as possible to be NOT NULL because you want to be sure data is always there.
217772
In JavaScript null is "nothing". It is supposed to be something that doesn't exist. Unfortunately, in JavaScript, the data type of null is an object. You can consider it a bug in JavaScript that typeof null is an object.
828821
Generally, NULL data represents data does not exist or missing data or unknown data. IS NULL & IS NOT NULL in SQL is used with a WHERE clause in SELECT, UPDATE and DELETE statements/queries to validate whether column has some value or data does not exist for that column. Please note that NULL and 0 are not same.
797695
and zero is an integer constant. So basically NULL is 0 in pointer terms. In SQL databases this difference is very important. NULL in SQL basically means that the value is 'undefined' whereas 0 is a defined value.
1380990
Null has no bounds, it can be used for string, integer, date, etc. fields in a database. Empty string is just regarding a string; it's a string like 'asdfasdf' is, but is just has no length.
1222297
So, in review: Null means the variable does not exist. Empty means it exists, but it contains no value. Zero length means an array or similar structure has been declared — and, if the language is strongly typed, has type — but contains no values.
526391
If you are using LEN(...) to determine whether the field is NULL or EMPTY then you need to use it as follows: ... WHEN LEN(ISNULL(MyField, '')) < 1 THEN NewValue...
681289
null checking shows you whether there is an object generally. isEmpty checking shows you whether the content of existing String object is empty.