Oracle模拟MySQL的show index from table命令
实验数据初始化:
显示该表所有索引的信息。
以dba登录
以普通用户登录
但是可以看到,以倒序创建的索引字段，都是以SYS等命名。
Oracle把这种倒序创建的索引字段看成函数索引。
它的信息保存在user_ind_expressions视图
user_ind_expressions视图的COLUMN_EXPRESSION字段类型是long型。
王工的版本可以解决这个问题
实验数据初始化:
-
create table t as select * from hr.employees;
-
create index inx_t1 on t(employee_id,first_name desc,last_name);
- create index inx_t2 on t(job_id,hire_date);
以dba登录
-
set linesize 300;
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set pagesize 100;
-
col c1 format a20;
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col c2 format a20;
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col c3 format a20;
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col c4 format a20;
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col c5 format a20;
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col INDEX_NAME format a20;
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select INDEX_NAME,
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max(decode(COLUMN_POSITION,1,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c1,
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max(decode(COLUMN_POSITION,2,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c2,
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max(decode(COLUMN_POSITION,3,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c3,
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max(decode(COLUMN_POSITION,4,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c4,
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max(decode(COLUMN_POSITION,5,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c5
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from (
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select INDEX_NAME,COLUMN_NAME,COLUMN_LENGTH,COLUMN_POSITION,DESCEND
-
from dba_ind_columns
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where table_owner='LIHUILIN'
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AND table_name='T'
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order by INDEX_NAME,column_position
- ) group by INDEX_NAME;
-
set linesize 300;
-
set pagesize 100;
-
col c1 format a20;
-
col c2 format a20;
-
col c3 format a20;
-
col c4 format a20;
-
col c5 format a20;
-
col INDEX_NAME format a20;
-
select INDEX_NAME,
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max(decode(COLUMN_POSITION,1,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c1,
-
max(decode(COLUMN_POSITION,2,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c2,
-
max(decode(COLUMN_POSITION,3,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c3,
-
max(decode(COLUMN_POSITION,4,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c4,
-
max(decode(COLUMN_POSITION,5,COLUMN_NAME||','||COLUMN_LENGTH||','||DESCEND,null)) c5
-
from (
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select INDEX_NAME,COLUMN_NAME,COLUMN_LENGTH,COLUMN_POSITION,DESCEND
-
from user_ind_columns
-
where table_name='T'
-
order by INDEX_NAME,column_position
- ) group by INDEX_NAME;
但是可以看到,以倒序创建的索引字段，都是以SYS等命名。
Oracle把这种倒序创建的索引字段看成函数索引。
它的信息保存在user_ind_expressions视图
user_ind_expressions视图的COLUMN_EXPRESSION字段类型是long型。
王工的版本可以解决这个问题
-
CREATE OR REPLACE FUNCTION long_2_varchar (
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p_index_name IN user_ind_expressions.index_name%TYPE,
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p_table_name IN user_ind_expressions.table_name%TYPE,
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p_COLUMN_POSITION IN user_ind_expressions.table_name%TYPE)
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RETURN VARCHAR2
-
AS
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l_COLUMN_EXPRESSION LONG;
-
BEGIN
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SELECT COLUMN_EXPRESSION
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INTO l_COLUMN_EXPRESSION
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FROM user_ind_expressions
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WHERE index_name = p_index_name
-
AND table_name = p_table_name
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AND COLUMN_POSITION = p_COLUMN_POSITION;
-
-
RETURN SUBSTR (l_COLUMN_EXPRESSION, 1, 4000);
-
END;
- /
-
set linesize 300;
-
set pagesize 100;
-
col c1 format a20;
-
col c2 format a20;
-
col c3 format a20;
-
col c4 format a20;
-
col c5 format a20;
-
col INDEX_NAME format a20;
-
SELECT INDEX_NAME,
-
MAX (DECODE (COLUMN_POSITION, 1, COLUMN_NAME || ' ' || DESCEND, NULL))
-
c1,
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MAX (DECODE (COLUMN_POSITION, 2, COLUMN_NAME || ' ' || DESCEND, NULL))
-
c2,
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MAX (DECODE (COLUMN_POSITION, 3, COLUMN_NAME || ' ' || DESCEND, NULL))
-
c3,
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MAX (DECODE (COLUMN_POSITION, 4, COLUMN_NAME || ' ' || DESCEND, NULL))
-
c4,
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MAX (DECODE (COLUMN_POSITION, 5, COLUMN_NAME || ' ' || DESCEND, NULL))
-
c5
-
FROM ( SELECT a.INDEX_NAME,
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REPLACE (
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DECODE (
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descend,
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'DESC', long_2_varchar (b.index_name,
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b.table_NAME,
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b.COLUMN_POSITION),
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a.column_name),
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'"',
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'')
-
COLUMN_NAME,
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a.COLUMN_LENGTH,
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a.COLUMN_POSITION,
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DESCEND
-
FROM user_ind_columns a
-
LEFT JOIN
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user_ind_expressions b
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ON a.index_name = b.index_name
-
AND a.table_name = b.table_name
-
WHERE a.table_name = 'T'
-
ORDER BY INDEX_NAME, column_position)
- GROUP BY INDEX_NAME;
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/29254281/viewspace-1193391/ ，如需转载，请注明出处，否则将追究法律责任。
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