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.
Related
I am a newbie in Oracle SQL, though I have experience in SQL Server.
In SQL Server, to select the rows from a table with a particular column in front:
select columnName,* from tableName
In Oracle:
select columnName,* from tableName
gives error ORA-00936: missing expression, as below:
Please guide.
I can't view images, but here's what I think you need:
select t.column_name, t.*
from table_name t
i.e. you should prefix that particular column name with a table alias ("t"), and then use the same alias with the asterisk ("t.*") to retrieve all table columns.
In Oracle, if you need to view a column but also all columns, you need to define an alias for the table.
Select columnName, A.*
from tableName A;
few things we need to keep it in mind
Alias name in sql - used to derive the individual column name via select query
When you are going to use *[select all] you don't have to worry about the alias name
But when you try to pull all the columns and some specific fields you want to filter then you should go for "Alias"
Alias its object key to refer the inter column
select stu.studentName,stu.* from student stu;
I'd like to select a 2 column from lot of table.
Exemple
Table_2017-01
id name value
Table_2017-02
id name value
Table_2017-03
id name value
etc...
My Query would be
SELECT name, value
FROM Table_2017-01, Table_2017-02, Table_2017-03
But I'd like to know if something it's possible like
SELECT name, value FROM LIKE Table_%
I know this last query is not possible and it could be easier for me if a query exist for this problem as I can have a lot of table with just a part of the name different.
To select mutiple columns with the same name you have to the table as prefix like:
SELECT `Table_2017-01.name`, `Table_2017-02.name`, `Table_2017-03.name` FROM Table_2017-01,`Table_2017-02, Table_2017-03
If you want them in one Column, use Union.
(SELECT `Table_2017-01.name` from Table_2017-01)
Union
(SELECT `Table_2017-02.name` from Table_2017-02)
It depends on your database. Oracle f.e. has a data dictionary with all tables.
Because I know oracle better than others I use this for the example:
SELECT TABLE_NAME FROM ALL_TABLES WHERE TABLE_NAME LIKE 'Table_2017-%';
Now there are the following ways I sometimes use:
I build a list of selects and fire them into the database:
via Excel (not explained here)
via SQL
SELECT
'SELECT '''||TABLE_NAME||''' TABLE_NAME, NAME, VALUE FROM '||
TABLE_NAME
||' UNION '
FROM ALL_TABLES WHERE TABLE_NAME LIKE 'Table_2017-%';
Now you can copy the result to your database (dont forget to delete the last "UNION")
via program (python, Lazarus, c# .. whatever, same view is needed)
But pay attention: It is quick and dirty, the column names and types have to match.
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 have a column name "CustomerIDClass" and I need to find the table it's associated with within an entire Oracle database.
I've run this to determine the owner and name of the table where this column name appears:
select * from DBA_TAB_COLUMNS
where COLUMN_NAME LIKE '%CustomerIDClass%';
and I'm getting this response:
I don't have enough reputation to post the image, so here's the link: http://i.imgur.com/a7rcKoA.png
I have no idea how to access this (BIN$Csew==) table. When I try to use it as a table name I get errors or messages saying that no rows were returned.
My main goal here is to write a simple statement that lets me search the database for the "CustomerIDClass" and view the table that contains this column name.
This table is in the recycle bin. You have to issue FLASHBACK TABLE "Customer1"."BIN$Csew==$0" TO BEFORE DROP command, given you have the appropriate privileges.
Doc: http://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_9012.htm
Do note that in oracle the column names are stored in capital but you are using mixed case in your like statement therefore the select clause will not return any result
Try the below
select * from DBA_TAB_COLUMNS
where COLUMN_NAME LIKE '%CUSTOMERIDCLASS%';
I'm using Oracle DB and I would like to write a SQL query that I could then call with JDBC. I'm not very familiar with SQL so if someone can help me, that could be great ! Here is the problem. I have a table MY_TABLE wich contains a list of another tables, and I would like to keep only the nonempty tables and those that their names start by a particular string.
The query I wrote is the following :
select TABLE_NAME
from MY_TABLE
where TABLE_NAME like '%myString%'
and (select count(*) from TABLE_NAME where rownum=1)<>0
order by TABLE_NAME;`
The problem comes from the second SELECT, but I don't know how can I do to use the TABLE_NAME value.
Does someone have an idea ?
Thanks.
[Added from comments]
Actually, I need to test the V$ 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;`