select a,b,null,null from table1 union select null,null,c,d from table2 union select null,null,null,null,e,f from table3.
Union select null, null, null, null, null, null, null from information_schema.tables. for a small database containing three tables. this instruction is used in sql injection I tried it and it worked but I didn't really know how it works can somebody help me...
Note: A NULL value is different from a zero value or a field that contains spaces.
union all select null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null
When SET CONCAT_NULL_YIELDS_NULL is ON, concatenating a null value with a string yields a NULL result.
create table fruitprices ( id tinyint unsigned not null auto_increment primary key, fruit_id tinyint unsigned not null, price int unsigned not null default 0
NULL is special in SQL. NULL indicates that the data is unknown, inapplicable or even does not exist.
In general, R supports: NULL NA NaN Inf / -Inf NULL is an object and is returned when an expression or function results in an undefined value.
The Oracle IS NOT NULL condition is used to test for a NOT NULL value.