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...
select cast (2000 as type of quint) from rdb$database select cast (2000 as int) from rdb$database.
Note: A NULL value is different from a zero value or a field that contains spaces.
ID in both tables will never be NULL. It IS possible that one of the tables may have ID values that are NOT in the other table.
SELECT customer_key as customer_key FROM customer_dimension t0 UNION ALL SELECT null AS customer_key FROM employee_dimension.
NULL is special in SQL. NULL indicates that the data is unknown, inapplicable or even does not
Each SELECT statement within the UNION ALL must have the same number of fields in the result sets with similar data types.
Существуют специальные операторы IS NULL и IS NOT NULL, которые позволяют производить сравнения с NULLами.
R language supports several null-able values and it is relatively important to understand how these values behave, when making data pre-processing and