I have many columns in oracle database and some new are added with values. I like to find out which columns have values other than 0 or null. So I am looking for column names for which some sort of useful values exists at least in one row.
How do I do this?
Update: This sounds very close. How do I modify this to suit my needs?
select column_name, nullable, num_distinct, num_nulls
from all_tab_columns
where table_name = 'SOME_TABLE'
You can query all the columns using the dba_tab_cols view and then see if there are columns which have values other than 0 or null.
create or replace function f_has_null_rows(
i_table_name in dba_tab_cols.table_name%type,
i_column_name in dba_tab_cols.table_name%type
) return number is
v_sql varchar2(200);
v_count number;
begin
v_sql := 'select count(*) from ' || i_table_name ||
' where ' || i_column_name ' || ' is not null and '
|| i_column_name || ' <>0 ';
execute immediate v_sql into v_count;
return v_count;
end;
/
select table_name, column_name from dba_tab_Cols
where f_has_null_rows (table_name, column_name) > 0
If you have synonyms in some schemas, you mighty find some of the tables are repeated. You'll have to change the code to cater to that.
Also, the check "is not equal to zero" might not be valid for columns that are not integers and will give errors if columns are of date datatype. You'll need to add the conditions for those cases. use the Data_type column in dba_tab_cols and add the condition as needed.
Select Column_name
from user_tab_columns
where table_name='EMP' and num_nulls=0;
This finds columns which does not have any values so you can perform any actions to that.
Sorry, I misread the question the first time.
From this post on Oracle's forums
Assuming your stats are up to date:
SELECT t.table_name,
t.column_name
FROM user_tab_columns t
WHERE t.nullable = 'Y'
AND t.num_distinct = 0;
Will return you a list of table names and columns that are null. You might want to add something like:
AND t.table_name = upper('Your_table_name')
in there to limit the results to just your table.
select 'cats' as mycolumname from T
where exists (Select id from T where cats is not null)
union
select 'dogs' as mycolumnname from T
where exists (select id from T where dogs is not null)
# ad nauseam
is how to do it in SQL. EDIT: Different flavors of SQL might let you optimize with LIMIT or TOP 'n' in the subquery. Or maybe they're even smart enough to realize that EXIST() only needs one row and optimize silently/transparently. P.S. Add your test for zero to the subquery.
Related
I am trying to loop through 5 tables all with a similar naming format. I am able to return the tables names by using the query
select table_name from all tables
where table_name like '
order by table_name
My intention is to insert the data from all the 5 tables into one table where a particular date condition is met. I know I can do this via union all but this makes my script very long as I have to paste the same script for 5 tables, I was wondering if there is a way to do without using union all but rather using dynamic sql? I am new to dynamic sql.
It might look like this:
begin
for cur_r in (select table_name
from all_tables
where table_name like 'ABC%'
)
loop
execute immediate
'insert into target_table (id, name, address) ' ||
'select id, name, address from ' || cur_r.table_name ||
' where date_column = ' || trunc(sysdate);
end loop;
end;
/
loop through all_tables, fetching only those you're interested in
compose insert statement, presuming that all tables (from previous step) share the same set of common columns
include where clause, if you want
I am trying to find how many occurrences of a particular value there are in a particular column in an Oracle database. The column is used in dozens of tables and I'm going to have to run the queries many times, so I don't want to query each table individually. I can get a list of the tables to search with something like:
Select table_name from all_tab_cols
join all_tables using (table_name)
where column_name = 'EmployeeId' and num_rows > 0
The next step is to iterate through that list of table names and output each table that contains a particular value in the EmployeeId column. For example, output might be something like:
**Table Name Column_name # Rows for EmployeeId = '123456'**
Table 1 EmployeeId 1
Table 2 EmployeeId 12
etc.
I'm not a developer and don't have experience using cursors in SQL scripts, so any help would be greatly appreciated.
try using CURSOR FOR LOOP.
Probably it may look as shown below (not tried).
BEGIN
FOR item IN
(Select table_name,column_name,num_rows from all_tab_cols
join all_tables using (table_name)
where column_name = 'EmployeeId' and num_rows > 0)
LOOP
DBMS_OUTPUT.PUT_LINE
(item.table_name || ' ' || item.column_name ||' '||item.num_rows);
END LOOP;
END;
I have a table as shown below. This table will be generated dynamically and I have no prior idea about what value it is going to hold.
------------------------------------------
TABLE_NAME COLUMN_NAME CHAR_LENGTH
------------------------------------------
EMPLOYEE COL1 100
EMPLOYEE COL2 200
EMPLOYEE COL3 300
EMPLOYEE COL4 400
Based on this table, I want to build a query in such a way that it would give me those columns, that contains data having char length greater than CHAR_LENGTH column value.
For example if COL2 contains data having char length 500 (>200), then query would give me COL2.
I don't have any draft code to show my attempt, as I have no idea how would I do this.
I don't think this is possible in pure SQL due to the dynamic nature of your requirement. You'll need some form of PL/SQL.
Assuming you're ok with simply outputting the desired results, here is a PL/SQL block that will get the job done:
declare
wExists number(1);
begin
for rec in (select * from your_dynamic_table)
loop
execute immediate 'select count(*)
from dual
where exists (select null
from ' || rec.table_name || ' t
where length(t.' || rec.column_name || ') > ' || rec.char_length || ')'
into wExists;
if wExists = 1 then
dbms_output.put_line(rec.column_name);
end if;
end loop;
end;
You'll also notice the use of the exists clause to optimize the query, so as not to iterate over the whole table unnecessarily, when possible.
Alternatively, if you want the results to be queryable, you can consider converting the code to a pipelined function.
select column_name
from (
select statement that builds the table output
) A
where char_length<length(column_name)
will that help?
You would need a procedure to achieve the same :
Here I am treating the all_tab_columns table in Oracle, which is a default table with much similar structure as your reference example.(Try select * from all_tab_columns). The structure of all_tab_columns is much like yours, except that you will never find a varchar record whose value has exceeded its data length(obvious database level constraint). Date fields may exceed data length, and do reflect in this procedure's output. I am searching all columns in EMPLOYEES whose size exceeds what is specified.
DECLARE
cursor c is select column_name,data_length,table_name from all_tab_columns where table_name=:Table_name;
V_INDEX_NAME all_tab_columns.column_name%type;
v_data_length all_tab_columns.data_length%type;
V_NUMBER PLS_INTEGER;
v_table_name all_tab_columns.table_name%type;
BEGIN
open c;
LOOP
FETCH c into v_index_name,v_data_length,v_table_name;
EXIT when c%NOTFOUND;
v_number :=0;
execute immediate 'select count(*) from '|| :Table_name ||' where length('||v_index_name||')>'||v_data_length into v_number;
if v_number>1 then
dbms_output.put_line(v_index_name||' has values greater than specified'||' '||V_INDEX_NAME||' '||v_data_length);
end if;
END LOOP;
close c;
END;
/
Replace all_tab_columns and its respective columns with the column name of your table.
DEFECTS : The table name is hardcoded. Trying to make the code generic execute immediate or any other trick. Will achieve soon.
EDIT : Defect fixed.
I have some big tables (30+ columns) with NOT NULL constraints. I would like to change all those constraints to NULL. To do it for a single column I can use
ALTER TABLE <your table> MODIFY <column name> NULL;
Is there a way to do it for all columns in one request ? Or should I copy/paste this line for all columns (><) ?
Is there a way to do it for all columns in one request ?
Yes. By (ab)using EXECUTE IMMEDIATE in PL/SQL. Loop through all the columns by querying USER_TAB_COLUMNS view.
For example,
FOR i IN
( SELECT * FROM user_tab_columns WHERE table_name = '<TABLE_NAME>' AND NULLABLE='N'
)
LOOP
EXECUTE IMMEDIATE 'ALTER TABLE <TABLE_NAME> MODIFY i.COLUMN_NAME NULL';
END LOOP;
In my opinion, by the time you would write the PL/SQL block, you could do it much quickly by using a good text editor. In pure SQL you just need 30 queries for 30 columns.
For a single table you can issue a single alter table command to set the listed columns to allow null, which is a little more efficient than running one at a time, but you still have to list every column.
alter table ...
modify (
col1 null,
col1 null,
col3 null);
If you were applying not null constraints then this would be more worthwhile, as they require a scan of the table to ensure that no nulls are present, and (I think) an exclusive table lock.
You can query user_tab_cols and combine it with a FOR cursor & EXECUTE IMMEDIATE to modify all not null columns - the PL/SQL block for doing like that would look like so:
DECLARE
v_sql_statement VARCHAR2(2000);
BEGIN
FOR table_recs IN (SELECT table_name, column_name
FROM user_tab_cols
WHERE nullable = 'N') LOOP
v_sql_statement :=
'ALTER TABLE ' || table_recs.table_name || ' MODIFY ' || table_recs.column_name || ' NULL';
EXECUTE IMMEDIATE v_sql_statement;
END LOOP;
END;
If you want to do it for all columns in a database instead of the ones in current schema, you can replace user_tab_cols and put in dba_tab_cols; I'd just run the query in the FOR to ensure that the columns being fetched are indeed the correct ones to be modified
I have a problem in that I want my output to be a single table (lets call it Output) with 2 columns: one for the "TableName" and one for the DateTime of the last update (using the scn_to_timestamp(max(ora_rowscn)) command).
I have 100 tables and I want to pull in the last update date/times for all these tables into the Output table.
So I can do this:
insert into Output(TableName)
select table_name
from all_tables;
which will put all the tables I have from my database into the TableName column. But I don't know how to loop through each entry and use the tablename as a variable and pass this into the scn_to_timestamp(ora_rowscn).
I thought I would try something like below:
for counter in Output(TableName) LOOP
insert into Output(UpdateDate)
select scn_to_timestamp(max(ora_rowscn))
from counter;
END LOOP;
Any suggestions?
Thank you
This query is a little bit clumsy as it uses xmlgen to execute dynamic sql in a query, but it might work for you.
select x.*
from all_tables t,
xmltable('/ROWSET/ROW' passing
dbms_xmlgen.getxmltype('select ''' || t.table_name ||
''' tab_name, max(ora_rowscn) as la from ' ||
t.table_name)
COLUMNS tab_name varchar2(30) PATH 'TAB_NAME',
max_scn number PATH 'LA') x
Here is a sqlfiddle demo
You can also use PLSQL and then use execute immediate