2 主键生成策略

<?id?name="id"?column="id">???
????<?generator?class="hilo">???
??????<?param?name="table">high_val<?/param>???
???????<?param?name="column">nextval<?/param>???
??????<?param?name="max_lo">5<?/param>???
????<?/generator>???
<?/id>??5、sequencehilo：同过高低位合成id，建一个sequence序列，不用建表。?
<?id?name="id"?column="id">???
<?generator?class="hilo">???
<?param?name="sequence">high_val_seq<?/param>???
<?param?name="max_lo">5<?/param>???
<?/generator>???
<?/id>?6、assigned：用户自定义id;?
<id?name="id"?type="string"?unsaved-value="null">?
??????<column?name="USER_ID"/>?
??????<generator?class="uuid.hex"/>?
</id>?


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