查询一个表的列数
我现在需要查询一个数据表的列数，请问一个SQL语句怎么实现啊？
[解决办法]
SELECT COUNT(*) FROM user_tab_columns
WHERE table_name= ?;
[解决办法]
select count(column_id)
from user_tab_columns
where table_name='YOUR_TABLE_NAME';
-- 注意表名的大小写格式！(默认表名应该是大写)
--1.通过查看表可以知道列数
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
--2.通过计算user_tab_columns视图中的column_id的个数
SQL> select count(column_id)
2 from user_tab_columns
3 where table_name='EMP';
COUNT(COLUMN_ID)
----------------
8
--我们来看看user_tab_columns视图的结构
SQL> 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
DATA_PRECISION NUMBER Y Length: decimal digits (NUMBER) or binary digits (FLOAT)
DATA_SCALE NUMBER Y Digits to right of decimal point in a number
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
