I want a query that returns me name of columns of a table.
I tried following query -
SELECT column_name ColName
FROM all_tab_columns
WHERE table_name ='<TABLENAME>';
but this query is returning duplicate column names.
I do not want to use distinct in my query cause it hampers the performance.
So is there a query which returns columns of a table without any duplicate.
This is the solution for getting column name from table.
select column_name,data_type from cols where Table_name='TEST_TABLE'
Related
I am using the sql command SHOW COLUMNS in this way
SHOW COLUMNS FROM TABLE A;
It outputs multiple columns, specifically one called 'COLUMN_NAME' that I would like to select.
I tried doing
SELECT COLUMN_NAME FROM (SHOW COLUMNS FROM TABLE A);
which gives an error, is there another way I can just show one of the columns of the output? Is this because the output is not a table so I cannot query from it?
You can use the like function:
show columns like 'COLUMN_NAME' in table A;
There are limitations on using the output of the show command, so an alternate approach is to use the INFORMATION_SCHEMA.
select * from INFORMATION_SCHEMA.COLUMNS where
TABLE_SCHEMA = 'MY_SCHEMA'
and TABLE_NAME = 'A'
and COLUMN_NAME = 'COLUMN_NAME';
If you need to query the results of a show command, you can use the result_scan table function:
show columns like '%' in table t1;
select * from table(result_scan(last_query_id())) where "column_name" = 'COLUMN_NAME';
Remember to double quote the column names produced by the show command. It's a metadata result and the column names are lower case.
select COLUMN_NAME
from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME='Submenu';
The above query gave all column names in Submenu table but I want only three column names of Submenu table.
Is there any way to get column names?
I assumed this is SQL Server, so the below queries might not work on other RDBMS's).
If your question is how to find only the column names you need (presuming you know in advance which ones those are), you would have to do something like this:
SELECT
COLUMN_NAME
FROM
INFORMATION_SCHEMA.COLUMNS
WHERE
TABLE_NAME='Submenu'
AND COLUMN_NAME IN ('Column1', 'Column2', 'Column3')
At this moment, you basically are requesting a list of any column within your table, without any restrictions whatsoever.
Alternatively, if you're looking only for the first three column names, this would work:
SELECT TOP 3
COLUMN_NAME
FROM
INFORMATION_SCHEMA.COLUMNS
WHERE
TABLE_NAME='Submenu'
ORDER BY
ORDERINAL_POSITION
In the latter case, you will have to determine how you want to sort the column names though (either by using something like ORDER BY COLUMN_NAME, in case you want them listed alphabetically, or ORDER BY ORDERINAL_POSITION in case you're trying to get them in the order they appear in the table).
If this is not what you meant, please elaborate on what you are trying to achieve.
SELECT TOP 3 COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'Submenu';
As easy as that!
Is it possible to select the first 20 columns from my table, without naming out each column in the select?
The columns are always ordered in the same way when I do a select, so there must be some underlying order.
The below query forms the SQL for you. It uses the dictionary table all_tab_columns to fetch the column names for the table.
SELECT ' SELECT '
|| REPLACE(LISTAGG(column_name,',') WITHIN GROUP( ORDER BY column_id),',',','
||CHR(10))
|| ' FROM YOUR_TABLE'
FROM all_tab_columns
WHERE owner ='YOUR_SCHEMA_NAME'
AND table_name='YOUR_TABLE_NAME'
AND column_id <= 20;
you can use column index instead of column name like select 0,1,2,.....
There is a table in a SQL Server database called sysColumns that records all the columns in every table. I think it is a SQL standard and should be in Oracle too.
EDIT: thanks to comment from #davegreen100, this table is in Oracle but is named DBA_TAB_COLUMNS.
try running Select * from DBA_TAB_COLUMNS and see what the results are, and work from there.
If it's there (in Oracle), you will eventually end up with something like
Select name from DBA_TAB_COLUMNS
Where id = #tableId -- <--- the id of the table
and colOrder <= 20
Your final SQL will be probably have to be generated dynamically using the output from the above
I am trying to build a query to fetch columns from the system.CATALOG table and to continue querying based on the resultset. I looked at a few queries but seem to be unable to find anything that satisfies my requirements. I don't have much to show, that I have tried as I don't know, how to approach this.
I am using Apache Phoenix DB. (Any SQL is also OK, as I am interested in learning.)
I have now written the query below, which will fetch me all the column names, that start with A in schema test for table element.
SELECT
COLUMN_NAME
FROM SYSTEM.CATALOG
WHERE TABLE_SCHEM = 'TEST'
AND TABLE_NAME = 'ELEMENT'
AND COLUMN_NAME LIKE 'A%'";
Now I want to use the list of columns names in an UPSERT query from the resultset of above query, to update these columns in the element table's records. So I am stuck here.
try this, it works perfect.
SELECT column_name
FROM system.catalog
WHERE table_name = 'your_table' AND key_seq IS NOT NULL
Example: To get the salt buckets on the table :
select table_name, salt_buckets
from SYSTEM.CATALOG
where salt_buckets is not null and table_name='TABLE_NAME';
How can I select the column name and table name from a SQL?
I tried something like this but it didn't work:
select column_name, table_name from (select * from users);
This might sound silly, but I have a list of different SQLs and I need to extract their columns and tables into a list. So some of the statements could me:
select username, password from users
select createdate from userlog
select * from dept
...
If I can select the column name and table name of a select statement, then I should get, say for the first statement, username and password for columns and users for table name. And createdate for column and userlog for table name in the second statement.
Then if it all works, I can then loop through the list of select statements and extract their column and table names.
The below query worked for Oracle database.
SELECT COLUMN_NAME,TABLE_NAME FROM ALL_TAB_COLUMNS
You can see more about information-schema
Edit:
You may try like this:
SELECT COLUMN_NAME,TABLE_NAME FROM ALL_TAB_COLUMNS
WHERE TABLE_NAME IN (SELECT ColumnName FROM users)
You need to parse the SQL statement so the SQL engine figures out the columns and datatypes of the columns that the statement returns.
How you do it best depends on what environment you are using. In some programming languages when you create a SqlPreparedStatement or OraCommand or whatever the object may be called, that object may have a metadata collection populated with column information after parsing.
If you are doing it in the database itself, parsing your statement with DBMS_SQL can get you the information you need. See Example 8 in the documentation at this link:
http://docs.oracle.com/database/121/ARPLS/d_sql.htm#ARPLS68205
--
Oh, and this gives you column names of the select statement. The table names I do not know of any way to get easily.