MySQL|并发控制

基于封技术、基于时戳技术、基于有效性检查、MVCC 等技术是并发控制技术

代码语言：javascript复制

mysql> create table z (
    -> a int not null,
    -> b int null,
    -> c int not null,
    -> d int not null,
    -> unique key (b),
    -> unique key (d),
    -> unique key (c));
Query OK, 0 rows affected (0.09 sec)

mysql> insert into z select 1,2,3,4;
Query OK, 1 row affected (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into z select 5,6,7,8;
Query OK, 1 row affected (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into z select 9,10,11,12;
Query OK, 1 row affected (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> select a,b,c,d,_rowid from z;
 --- ------ ---- ---- -------- 
| a | b    | c  | d  | _rowid |
 --- ------ ---- ---- -------- 
| 1 |    2 |  3 |  4 |      4 |
| 5 |    6 |  7 |  8 |      8 |
| 9 |   10 | 11 | 12 |     12 |
 --- ------ ---- ---- -------- 
3 rows in set (0.02 sec)

d列先定义，所以d被先定义为主键

代码语言：javascript复制

mysql> create table a(
    -> a int,
    -> b int,
    -> primary key(a,b)
    -> )engine=InnoDB;
Query OK, 0 rows affected (0.04 sec)

mysql> insert into a select 1,1
    -> ;
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> select a,_rowid from a;
ERROR 1054 (42S22): Unknown column '_rowid' in 'field list'
mysql>

如果是多个列定义到主键，则_rowid无法获取主键

mysql 并发

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