如何从表中选择具有非null值的列? [英] How to select columns from a table which have non null values?
问题描述
我有一个包含数百个列的表,其中许多为空,我想使用我的select语句,以便仅返回那些包含值的列.这将帮助我更好地分析数据.像这样:
I have a table containing hundreds of columns many of which are null, and I would like have my select statement so that only those columns containing a value are returned. It would help me analyze data better. Something like:
从表名中选择(非空列);
Select (non null columns) from tablename;
我想选择所有具有至少一个非空值的列.
I want to select all columns which have at least one non-null value.
可以做到吗?
推荐答案
作为统计信息的外观,它可能对您有用:
Have a look as statistics information, it may be useful for you:
SQL> exec dbms_stats.gather_table_stats('SCOTT','EMP');
PL/SQL procedure successfully completed.
SQL> select num_rows from all_tables where owner='SCOTT' and table_name='EMP';
NUM_ROWS
----------
14
SQL> select column_name,nullable,num_distinct,num_nulls from all_tab_columns
2 where owner='SCOTT' and table_name='EMP' order by column_id;
COLUMN_NAME N NUM_DISTINCT NUM_NULLS
------------------------------ - ------------ ----------
EMPNO N 14 0
ENAME Y 14 0
JOB Y 5 0
MGR Y 6 1
HIREDATE Y 13 0
SAL Y 12 0
COMM Y 4 10
DEPTNO Y 3 0
8 rows selected.
例如,您可以检查NUM_NULLS = NUM_ROWS以标识空"列.
参考: ALL_TAB_COLUMNS , ALL_TABLES .
For example you can check if NUM_NULLS = NUM_ROWS to identify "empty" columns.
Reference: ALL_TAB_COLUMNS, ALL_TABLES.
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