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 |
+------+------+-------+------------+

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