创建索引 [英] Creation of index

问题描述

在sql中创建表后如何在主键上创建索引?

How to create index on primary key after creation of table in sql?

推荐答案

如果您使用主键约束创建了表，那么您在属于PK的字段上已经具有唯一索引；该索引是在添加PK约束时创建的，其名称不具有任何含义:

If you created the table with the primary key constraint, then you already have a unique index on the fields belonging to the PK; this index has been created when you added the PK constraint and has a not significative name:

SQL> create table TEST_PK_IDX(id number primary key, descr varchar2(100));

Table created.

SQL> select index_name, uniqueness, column_name
  2  from user_ind_columns c
  3         inner join user_indexes i
  4           using (index_name)
  5  where i.table_name = 'TEST_PK_IDX';

INDEX_NAME           UNIQUENESS           COLUMN_NAME
-------------------- -------------------- --------------------
SYS_C007838          UNIQUE               ID

但是，如果需要创建其他索引，则可以使用:

However, if you need to create a different index, you can use:

SQL> create index idx_test on test_pk_idx(descr);

Index created.

SQL> select index_name, uniqueness, column_name
  2  from user_ind_columns c
  3         inner join user_indexes i
  4           using (index_name)
  5  where i.table_name = 'TEST_PK_IDX';

INDEX_NAME           UNIQUENESS           COLUMN_NAME
-------------------- -------------------- --------------------
SYS_C007838          UNIQUE               ID
IDX_TEST             NONUNIQUE            DESCR

SQL>

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