比如我们想查看一个表中某个列的默认值情况，可以查询user_tab_cols,或者dba_tab_cols等，字段data_default是Long类型。
SQL> desc user_tab_cols
Name Null? Type
----------------------------------------- -------- ----------------------------
TABLE_NAME NOT NULL VARCHAR2(30)
COLUMN_NAME NOT NULL VARCHAR2(30)
DATA_TYPE VARCHAR2(106)
DATA_TYPE_MOD VARCHAR2(3)
DATA_TYPE_OWNER VARCHAR2(120)
DATA_LENGTH NOT NULL NUMBER
DATA_PRECISION NUMBER
DATA_SCALE NUMBER
NULLABLE VARCHAR2(1)
COLUMN_ID NUMBER
DEFAULT_LENGTH NUMBER
DATA_DEFAULT LONG
NUM_DISTINCT NUMBER
LOW_VALUE RAW(32)
HIGH_VALUE RAW(32)
DENSITY NUMBER
NUM_NULLS NUMBER
NUM_BUCKETS NUMBER
LAST_ANALYZED DATE
SAMPLE_SIZE NUMBER
CHARACTER_SET_NAME VARCHAR2(44)
CHAR_COL_DECL_LENGTH NUMBER
GLOBAL_STATS VARCHAR2(3)
USER_STATS VARCHAR2(3)
AVG_COL_LEN NUMBER
CHAR_LENGTH NUMBER
CHAR_USED VARCHAR2(1)
V80_FMT_IMAGE VARCHAR2(3)
DATA_UPGRADED VARCHAR2(3)
HIDDEN_COLUMN VARCHAR2(3)
VIRTUAL_COLUMN VARCHAR2(3)
SEGMENT_COLUMN_ID NUMBER
INTERNAL_COLUMN_ID NOT NULL NUMBER
HISTOGRAM VARCHAR2(15)
QUALIFIED_COL_NAME VARCHAR2(4000)
如果想使用Like来模糊匹配或者重新创建一个临时表，都会碰到Long类型的问题。
select *from user_tab_cols where data_default like 'a%'
*
ERROR at line 1:
ORA-00932: inconsistent datatypes: expected NUMBER got LONG
SQL> create table t1 as select *from user_tab_cols;
create table t1 as select *from user_tab_cols
*
ERROR at line 1:
ORA-00997: illegal use of LONG datatype
既然不支持，Oracle也提供了对应的一些方法来满足我们的需要。
在thomas kyte的书中，对这种实现方法做了详细的解释。
使用的代码如下，基本就是把Long类型转换为varchar2,按照每批4000个字节的容量进行转换。
create or replace package long_help authid current_user as function substr_of(p_query in varchar2, p_from in number, p_for in number, p_name1 in varchar2 default NULL, p_bind1 in varchar2 default NULL, p_name2 in varchar2 default NULL, p_bind2 in varchar2 default NULL, p_name3 in varchar2 default NULL, p_bind3 in
varchar2 default NULL, p_name4 in varchar2 default NULL, p_bind4 in varchar2 default NULL) return varchar2;
end;
/
create or replace package body long_help as
g_cursor number := dbms_sql.open_cursor;
g_query varchar2(32765);
procedure bind_variable(p_name in varchar2, p_value in varchar2) is
begin
if (p_name is not null) then dbms_sql.bind_variable(g_cursor, p_name, p_value);
end if;
end;
function substr_of(p_query in varchar2, p_from in number, p_for in number, p_name1 in varchar2 default NULL, p_bind1 in varchar2 default NULL, p_name2 in varchar2 default NULL, p_bind2 in varchar2 default NULL, p_name3 in varchar2 default NULL, p_bind3 in varchar2 default NULL, p_name4 in varchar2 default NULL, p_bind4 in varchar2 default NULL) return varchar2 as
l_buffer varchar2(4000); l_buffer_len number;
begin
if (nvl(p_from, 0) = 1 (positive numbers)');
end if;
if (nvl(p_for, 0) not between 1 and 4000) then raise_application_error(-20003, 'For must be between 1 and 4000');
end if;
if (p_query g_query or g_query is
NULL) then if (upper(trim(nvl(p_query, 'x'))) not like 'SELECT%') then raise_application_error(-20001, 'This must be a select only');
end if;
dbms_sql.parse(g_cursor, p_query, dbms_sql.native); g_query := p_query;
end if;
bind_variable(p_name1, p_bind1); bind_variable(p_name2, p_bind2); bind_variable(p_name3, p_bind3); bind_variable(p_name4, p_bind4); dbms_sql.define_column_long(g_cursor, 1); if (dbms_sql.execute_and_fetch(g_cursor) > 0) then dbms_sql.column_value_long(g_cursor, 1, p_for, p_from - 1, l_buffer, l_buffer_len);
end if;
return l_buffer;
end substr_of;
end;
/
这个时候我们想查询data_default的值就可以使用如下的sql
SELECT *
FROM (SELECT OWNER,
TABLE_NAME,
COLUMN_NAME,
DATA_TYPE,
LONG_HELP.SUBSTR_OF('SELECT data_default FROM DBA_TAB_COLS WHERE OWNER=:OWNER AND TABLE_NAME=:TABLE_NAME AND COLUMN_NAME=:COLUMN_NAME',
1,
4000,
'OWNER',
OWNER,
'TABLE_NAME',
TABLE_NAME,
'COLUMN_NAME',
COLUMN_NAME) DATA_DEFAULT
FROM DBA_TAB_COLS);
查询结果如下：
OWNER TABLE_NAME COLUMN_NAME DATA_TYPE DATA_DEFAULT
-------------------- ------------------------------ ------------------------------ ------------------------------ ------------------------------
SYS RECO_SCRIPT_BLOCK$ CTIME DATE SYSDATE
SYS RECO_SCRIPT_BLOCK$ SPARE1 NUMBER
SYS RECO_SCRIPT_BLOCK$ SPARE2 NUMBER
SYS RECO_SCRIPT_BLOCK$ SPARE3 NUMBER
SYS RECO_SCRIPT_BLOCK$ SPARE4 VARCHAR2
SYS RECO_SCRIPT_BLOCK$ SPARE5 VARCHAR2
SYS RECO_SCRIPT_BLOCK$ SPARE6 DATE
SYS STREAMS$_COMPONENT_LINK SOURCE_COMPONENT_ID NUMBER
SYS STREAMS$_COMPONENT_LINK DEST_COMPONENT_ID NUMBER
SYS STREAMS$_COMPONENT_LINK PATH_ID NUMBER
SYS STREAMS$_COMPONENT_LINK POSITION NUMBER
