I'm using Oracle DB and I would like to write a SQL query that I could then call with JDBC. I'm not very familiar with SQL so if someone can help me, that could be great ! Here is the problem. I have a table MY_TABLE wich contains a list of another tables, and I would like to keep only the nonempty tables and those that their names start by a particular string.
The query I wrote is the following :
select TABLE_NAME
from MY_TABLE
where TABLE_NAME like '%myString%'
and (select count(*) from TABLE_NAME where rownum=1)<>0
order by TABLE_NAME;`
The problem comes from the second SELECT, but I don't know how can I do to use the TABLE_NAME value.
Does someone have an idea ?
Thanks.
[Added from comments]
Actually, I need to test the V$ views contained in the ALL_CATALOG table. But if I can find another table where all these views are contained too and with a NUM_ROWS column too, it would be perfect !
Standard versions of SQL do not allow you to replace 'structural elements' of the query, such as table name or column name, with variable values or place-holders.
There are a few ways to approach this.
Generate a separate SQL statement for each table name listed in MY_TABLE, and execute each in turn. Brute force, but effective.
Interrogate the system catalog directly.
Investigate whether there are JDBC metadata operations that allow you to find out about the number of rows in a table without being tied to the system catalog of the specific DBMS you are using.
Can you use oracle view USER_TABLES? then query will be much easier
select TABLE_NAME
from USER_TABLES
where TABLE_NAME like '%myString%'
and Num_ROWS > 0
order by TABLE_NAME;`
Related
I have so far figured out that to describe a table I can use the below:
select dbms_metadata.get_ddl('TABLE','<my table name>','<table owner>') from dual;
I also found that I can get a list of tables from the current user using the below statement:
select table_name from user_tables;
However I need to find a way to combine these two so I get a (preferably SQL file) output which basically describes all the tables in the current schema. How can I go about that?
Call dbms_metadata in your query on user_tables:
select dbms_metadata.get_ddl('TABLE',table_name,user)
from user_tables;
I'm going through all tables in a database trying to determine which tables are old (have not been altered in a long time). I've been going through and flagging all tables with old DTS's as "old"
Is there a more efficient way to do this? Can I run a statement that scans all tables in a database for date-timestamp fields and then looks at the most recent ones?
Thank you in advance for any help you can provide!
You can use the INFORMATION_SCHEMA.COLUMNS view to retrieve all the tables having the timestamp column (assuming the column name is known and not used for other columns).
Use these to generate Dynamic SQL of the form
SELECT COUNT(*) ,#TableName FROM #TableName WHERE #TimeStampColumn < #TimestampToCheck
The tables where count(*) is 0 are the ones you need to look at
I would do something like this:
Show a COUNT(*) of rows written in the last year... if you get 0, you know the table isn't in use.
Use the information_schema to get the columns/tables.
SELECT 'SELECT COUNT(*) AS ['+TABLE_NAME+'] FROM ['+TABLE_CATALOG+'].['+TABLE_SCHEMA+'].['+TABLE_NAME+'] WHERE '+COLUMN_NAME+' > DATEADD(YY,-1,CONVERT(DATETIME,FLOOR(CONVERT(FLOAT,GETDATE()))))'
-- SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE='DATETIME'
--AND (COLUMN_DEFAULT='(getdate())' OR COLUMN_DEFAULT='CURRENT_TIMESTAMP')
You can add the last line in, if you only want columns with a default value.
Then take the output, copy to a new window, and run it!
I am migrating data from MS SQL to Netezza and so I need to find the row counts of all tables in a database (in Netezza). Any query for the same would be of an immense help to me as I'm completely new to this. Thanks in advance.
This query does it directly from _v_table:
SELECT TABLENAME, RELTUPLES FROM _V_TABLE where objtype = 'TABLE' ORDER BY RELTUPLES
something like this should work:
select 'select '||chr(39)||tablename||chr(39)||' as entity, count(1) from '||tablename||' union all'
from _v_table
where object_type ='TABLE';
copy/paste the result, remove the last "union all".
I have never used Netezza but googled and found:
http://www.folkstalk.com/2009/12/netezza-count-analytic-functions.html
SELECT dept_id,
salary,
COUNT(1) OVER() total_cnt
FROM Employees
If you don't know what tables that exists:
http://www.folkstalk.com/2009/11/netezza-system-catalog-views.html
select * from _v_table;
Another way to acquire the row counts for a table (if you have access to the operating system level) is to use the Netezza nz_get_table_rowcount command. You can enter, "nz_get_table_rowcount -h" to get all of the help text on this command, but the format is:
Usage: nz_get_table_rowcount [database]
Purpose: Perform a "SELECT COUNT(*) FROM ;" to get its true rowcount.
Thus, this script results in a full table scan being performed.
Inputs: The database name is optional. If not specified, then $NZ_DATABASE
will be used instead.
The table name is required. If only one argument is specified, it
will be taken as the table name.
If two arguments are specified, the first will be taken as the
database name and the second will be taken as the table name.
Outputs: The table rowcount is returned.
Use this command in a shell script to cycle through all of the tables within a database. Use nz_get_table_names to get the list of tables within a database.
I am working with oracle10g. How can I determine the number of columns in a relation specified as a SQL query?
You need to take a look at DBMS_SQL package. A select statement can include n columns, thus you need to parse it manually using PL/SQL.
DBMS_SQL.REC_TAB structure will give you plenty of information about your select statement.
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14258/d_sql.htm
You can dba_tab_columns synonym.
SELECT COUNT(COLUMN_NAME) from DBA_TAB_COLUMNS
WHERE TABLE_NAME='NAME_HERE_RELATION';
The environment is Oracle 9 & 10. I do not have DBA level access.
The problem is to verify that a specific column exists in a specific table, in another schema.
There are two cases to deal with.
Another schema in the same instance
A schema in a different instance, using a db_link
Given my schema FRED and another schema BARNEY, I tried something like this
SELECT 1
FROM BARNEY.USER_TAB_COLS
WHERE TABLE_NAME = 'SOME_TABLE'
AND COLUMN_NAME = 'SOME_SPECIFIC_COLUMN'
Which yielded [1]: (Error): ORA-00942: table or view does not exist
After vegging on this awhile, I realized that USER_TAB_COLS, is not really a table. It is a view. I have been selecting from tables all along, but not from a view.
I tried the same thing with my db_link, and was surprised to see data come back. A db_link has an embedded schema_name/password in it, so it seems reasonable to me that it worked, as it effectively logs in to the other schema, which should make the views reachable.
Having Googled around, and worn out my eyeballs on on the mountain of Oracle doc,
I am looking for someone to point me in the correct direction, or at least point out what I am missing.
What techniques are available for getting user table related metadata from a schema in the same instance in order to validate that a specific column exists?
Thanks in advance.
Evil.
+1 for good answers.
Thank you.
You can use the following query:
SELECT 1
FROM ALL_TAB_COLS
WHERE TABLE_NAME = 'SOME_TABLE'
AND COLUMN_NAME = 'SOME_SPECIFIC_COLUMN'
AND OWNER = 'BARNEY';
(User_Tables and User_Tab_Cols are just views on all_tables and all_tab_coumns with a where owner = <Current User> attached to it)
If you're allowed to see the Barney's some_table (i.e. you have been GRANTed at least SELECT privileges on it), then you'll know if the column is there. If you have no rights on the table, you won't be able to get meta information on it.
As with the other replies, normally I use ALL_TAB_COLUMNS for a query like this. But that will only show columns in tables where you have SELECT. And it's select on that column -- in the unlikely event that they've implemented column-level privileges for that table, you may be able to see the table, but not see the specific column of interest. For most of us, that's extremely rare.
DBA_TAB_COLUMNS will show all columns, but you'll need select on it granted to your schema by your DBA. (Actually, you'll need a grant on ALL_TAB_COLUMNS to use it, but that's common in most shops). The DBMS_METADATA PL/SQL Built-in package can also be used, with similar limitations, but I think you'll find it more complicated.
Of course, you can also just try to select a record from barney.some_table.some_column#my_dblink (or whatever pieces of that you're interested in). And then handle the exception. Ugly, I wouldn't recommend it in most situations.
You would use all_tab_columns for that.
But beware that you'll only see what you are allowed to see.
Same instance, different schema:
Select Count(*)
From all_tab_cols
Where owner = 'BARNEY' and
table_name = 'SOME_TABLE' and
column_name = 'SOME_SPECIFIC_COLUMN';
The count(*) has the advantage of always returning a single row with a value of either 1 or 0, so you do not have to deal with NO_DATA_FOUND errors in PL/SQL.
Across a DB Link, same schema as the one you connect as:
Select Count(*)
From user_tab_cols#MY_DB_LINK
Where table_name = 'SOME_TABLE' and
column_name = 'SOME_SPECIFIC_COLUMN';
Across a DB Link, different schema than the one you connect as:
Select Count(*)
From all_tab_cols#MY_DB_LINK
Where owner = 'BARNEY' and
table_name = 'SOME_TABLE' and
column_name = 'SOME_SPECIFIC_COLUMN';