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天堂等于天下？是的，你的眼睛没有花~，看下面例子
mysql> create table t (a varchar(12) default null,b varchar(12) default null, unique key idx_a (a),unique key idx_b (b)) engine=innodb default charset=latin1;
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> insert into t values ("天堂",1);
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> insert into t values ("天下",1);
ERROR 1062 (23000): Duplicate entry '天下' for key 'idx_a'
mysql>
这是由于'天堂'和'天下'gbk编码在latin1_swedish_ci排序集下是相等的。
mysql> alter table t change a a varchar(20) CHARACTER SET latin1 collate latin1_bin; Query OK, 2 rows affected (0.00 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> mysql> insert into t values ("天下",2); Query OK, 1 row affected (0.00 sec) mysql>
mysql> insert into t values ('ABC','ABC'); Query OK, 1 row affected (0.00 sec) mysql> mysql> insert into t values ('abc','ABC'); ERROR 1062 (23000): Duplicate entry 'abc' for key 'idx_a' mysql>
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