oracle data_length和data_precision的区别

这两个属性都属于user_tab_columns视图，他们的含义：data_length:当前列数据类型的字节长度 如:EMPNO NUMBER(4) 22 ENAME VARCHAR2(10) 10data_precision:列相关数据类型(数字类型)的具体长度(有效位数),一个十进制数(NUMBER类型),或一个二进制树(FLOAT类型) 如:SAL NUMBER(7,2) 7//来看看user_tab_columns视图的相关信息,我们主要关注Name,Comments两列和带注释的三行：desc user_tab_columns;Name Type Nullable Default Comments -------------------- ------------- -------- ------- -------------------------------------------------------------------- TABLE_NAME VARCHAR2(30) Table, view or cluster name COLUMN_NAME VARCHAR2(30) Column name DATA_TYPE VARCHAR2(106) Y Datatype of the column DATA_TYPE_MOD VARCHAR2(3) Y Datatype modifier of the column DATA_TYPE_OWNER VARCHAR2(30) Y Owner of the datatype of the column DATA_LENGTH NUMBER Length of the column in bytes/*列的数据类型的字节长度*/ DATA_PRECISION NUMBER Y Length: decimal digits (NUMBER) or binary digits (FLOAT)/*数字类型的实际长度*/ DATA_SCALE NUMBER Y Digits to right of decimal point in a number/*小数点位数*/ NULLABLE VARCHAR2(1) Y Does column allow NULL values? COLUMN_ID NUMBER Y Sequence number of the column as created DEFAULT_LENGTH NUMBER Y Length of default value for the column DATA_DEFAULT LONG Y Default value for the column NUM_DISTINCT NUMBER Y The number of distinct values in the column LOW_VALUE RAW(32) Y The low value in the column HIGH_VALUE RAW(32) Y The high value in the column DENSITY NUMBER Y The density of the column NUM_NULLS NUMBER Y The number of nulls in the column NUM_BUCKETS NUMBER Y The number of buckets in histogram for the column LAST_ANALYZED DATE Y The date of the most recent time this column was analyzed SAMPLE_SIZE NUMBER Y The sample size used in analyzing this column CHARACTER_SET_NAME VARCHAR2(44) Y Character set name CHAR_COL_DECL_LENGTH NUMBER Y Declaration length of character type column GLOBAL_STATS VARCHAR2(3) Y Are the statistics calculated without merging underlying partitions? USER_STATS VARCHAR2(3) Y Were the statistics entered directly by the user? AVG_COL_LEN NUMBER Y The average length of the column in bytes CHAR_LENGTH NUMBER Y The maximum length of the column in characters CHAR_USED VARCHAR2(1) Y C is maximum length given in characters, B if in bytes V80_FMT_IMAGE VARCHAR2(3) Y Is column data in 8.0 image format? DATA_UPGRADED VARCHAR2(3) Y Has column data been upgraded to the latest type version format? HISTOGRAM VARCHAR2(15) Y//实例1:查看emp表的列对应的data_length,data_precision,data_scale实际值SQL> desc emp;Name Type Nullable Default Comments -------- ------------ -------- ------- -------- EMPNO NUMBER(4) ENAME VARCHAR2(10) Y JOB VARCHAR2(9) Y MGR NUMBER(4) Y HIREDATE DATE Y SAL NUMBER(7,2) Y COMM NUMBER(7,2) Y DEPTNO NUMBER(2) Y //select column_name,data_type,data_length,data_precision,data_scalefrom user_tab_columns where table_name='EMP';COLUMN_NAME DATA_TYPE DATA_LENGTH DATA_PRECISION DATA_SCALE------------------------------ ------------------------------- ----------- -------------- ----------EMPNO NUMBER 22 4 0ENAME VARCHAR2 10 JOB VARCHAR2 9 MGR NUMBER 22 4 0HIREDATE DATE 7 SAL NUMBER 22 7 2COMM NUMBER 22 7 2DEPTNO NUMBER 22 2 0 

原帖:http://topic.csdn.net/u/20110311/10/73fa722c-d119-4af4-8b6a-41fa3d9b2f06.html

oracle datatype:http://ss64.com/ora/syntax-datatypes.html