Mysql 分割槽處理NULL值的方式

一般情況下，mysql的分割槽把null當做零值，或者乙個最小值進行處理

對於range分割槽

create table test_null(

id int
)partition by range(id)(
partition p0 values less than (-6),
partition p1 values less than (0),
partition p2 values less than (1),
partition p3 values less than maxvalue
);mysql> insert into test_null values(null);
query ok, 1 row affected (0.01 sec)
mysql> select 
-> partition_name part, 
-> partition_expression expr, 
-> partition_description descr, 
-> table_rows 
-> from information_schema.partitions where 
-> table_schema = schema() 
-> and table_name='test_null';
+------+------+----------+------------+
| part | expr | descr | table_rows |
+------+------+----------+------------+
| p0 | id | -6 | 1 |
| p1 | id | 0 | 0 |
| p2 | id | 1 | 0 |
| p3 | id | maxvalue | 0 |
+------+------+----------+------------+
4 rows in set (0.00 sec)

當分割槽定義不包含null值是，會報錯

create table list_null(

id int
)partition by list(id)(
partition p1 values in (0),
partition p2 values in (1)
);mysql> insert into list_null values(null);
error 1526 (hy000): table has no partition
for value null

create table list_null_1(

id int
)partition by list(id)(
partition p1 values in (0),
partition p2 values in (1),
partition p3 values in (null)
);mysql> insert into list_null_1 values(null);
query ok, 1 row affected (0.01 sec)
mysql> select 
-> partition_name part, 
-> partition_expression expr, 
-> partition_description descr, 
-> table_rows 
-> from information_schema.partitions where 
-> table_schema = schema() 
-> and table_name='list_null_1';
+------+------+-------+------------+
| part | expr | descr | table_rows |
+------+------+-------+------------+
| p1 | id | 0 | 0 |
| p2 | id | 1 | 0 |
| p3 | id | null | 1 |
+------+------+-------+------------+
3 rows in set (0.00 sec)

create table hash_null(

id int
)partition by hash(id)
partitions 2;
mysql> insert into hash_null values(null);
query ok, 1 row affected (0.00 sec)
mysql> select 
-> partition_name part, 
-> partition_expression expr, 
-> partition_description descr, 
-> table_rows 
-> from information_schema.partitions where 
-> table_schema = schema() 
-> and table_name='hash_null';
+------+------+-------+------------+
| part | expr | descr | table_rows |
+------+------+-------+------------+
| p0 | id | null | 1 |
| p1 | id | null | 0 |
+------+------+-------+------------+
2 rows in set (0.00 sec)
對於key分割槽
create table key_null(
id int
)partition by key(id)
partitions 2;
mysql> select 
-> partition_name part, 
-> partition_expression expr, 
-> partition_description descr, 
-> table_rows 
-> from information_schema.partitions where 
-> table_schema = schema() 
-> and table_name='key_null';
+------+------+-------+------------+
| part | expr | descr | table_rows |
+------+------+-------+------------+
| p0 | `id` | null | 1 |
| p1 | `id` | null | 0 |
+------+------+-------+------------+

MySQL 處理 null 值的問題

mysql中null是不參與計算的，對null進行計算，使用 is null 和 is not null 運算子 只有 才支援null的比較，其他比較運算對有null運算元時返回的結果就是null，永遠返回false，即 null null 返回false 結論 如果在not in子查詢中有null...

mysql之null值處理函式

ifnull expr1,expr2 如果第乙個引數 expr1 不為null則直接返回它，否則返回第二個引數 expr2。返回值是數字或者字串。它相當於oracle中的nvl函式 select ifnull 1,0 select ifnull null,10 select ifnull 1 0,y...

空值NULL處理

1.空值 null 處理 查詢籍貫為null同學 如果判斷乙個欄位的的值是不是null，需要使用is關鍵字，不能使用 select from tbstudent where stuaddress isnull 查詢籍貫不是null的所有同學 select from tbstudent where s...