I have been researching this for a couple of days and feel like I am going around in circles. I have basic knowledge of SQL but there are many areas I do not understand.
I have a table that stores the names and fields of all the other tables in my database.
tblFields
===================================================
TableName FieldName BookmarkName
---------------------------------------------------
Customer FirstName CustomerFirstName
Customer LastName CustomerLastName
Customer DOB CustomerDOB
I want to write a SELECT statement like the following but i am unable to get it work:
SELECT (SELECT [FieldName] FROM [TableName]) FROM tblFields
Is this possible? The application I have developed requires this for user customization of reports.
If i understand what you are trying to do, i think this will help you. It is not pretty and it works for SQL Server 2005 and above, but maybe this is what you are looking for:
declare #tableName nvarchar(100)
declare #sqlQuery nvarchar(max)
declare #fields varchar(500)
set #tableName = 'YourTableName'
set #fields = ''
select #fields = #fields + QUOTENAME(t.fieldname) + ',' from (
select distinct fieldname from tblfields where tablename = #tableName)t
set #sqlQuery = 'select ' + left(#fields, LEN(#fields)-1) + ' from ' + QUOTENAME(#tableName)
execute sp_executesql #sqlQuery
Edit: As Martin suggested, i edited so that the columns and tablename are using QUOTENAME
If I understand correctly what you are trying to do, you are probably better off doing this as two separate queries from your program. One which gets the fields you want to select which you then use in your program to build up the second query which actually gets the data.
If it must be done entirely in SQL, then you will need to tell us what database you are using. If it is SQL Server, you might be able to user a cursor over the first query to build up the second query which you then execute with the sp_executesql stored procedure. But doing doing it outside of SQL would be recommended.
Related
I have this query in SQL Server:
select column
from table_53;
Now, I want to get this 53 from another table, so what I want to do is something like this:
select column
from table_(select id from table2);
Is there any way to do this in SQL Server?
This is definitely not the way SQL thinks and works. Maybe your suggested approach can be mimicked by way of writing stored procedures in which you create SQL-statements which are then evaluated. However, this will not be very efficient.
A better approach would be to store the values of all your individual separate tables into one master table and mark them in a separate column tblid with their number (e.g. 53). Then you can always filter them from this master table by looking for this tblid.
You need dynamic sql query here.
declare #sqlQuery = 'select column
from table_(';
set #sqlQuery = #sqlQuery + 'select id from table2)';
EXEC (#sqlQuery)
Note :- One of cons of using dynamic sql query is sql injection. I would suggest to have better table structure or try to used parameterized query.
Yes, you can, but using something like this:
DECLARE #ID INT;
DECLARE #QUERY NVARCHAR(MAX);
SELECT #ID = ID FROM TABLE_2;
--IF #ID EQUALS 53 THEN
SET #QUERY = 'SELECT COLUMN FROM TABLE_' + CAST(#ID AS NVARCHAR(10));
-- #QUERY EQUALS TO 'SELECT COLUMN FROM TABLE_53'
EXEC (#QUERY);
If I have a table that actually holds the table name and column name of another table like this:
TestTable
TheTable nvarchar
TheColumn nvarchar
Sudo Logic
SELECT
t.Something
,t.SomethingElse
,t.TheTable
,t.TheColumn
,(SELECT *TheColumn* FROM *TheTable*) AS Something
FROM TestTable t
Even writing this question I'm getting several suggestions of similar questions, but I'm hoping for a much simpler example if there is one, so no intention to duplicate a question. Other examples seem specific and are quite extensive.
Thank you.
Here's some dynamic sql loosely based on your sample code:
/* set up a few parameters */
DECLARE #table_name AS nvarchar(100)
DECLARE #column_name AS nvarchar(100)
DECLARE #SQLQuery AS NVARCHAR(1000)
/* set the parameter values */
SELECT #table_name=TheTable, #column_name=TheColumn
FROM TestTable
WHERE -- ADD SOME LOGIC HERE TO GET SINGLE ROW
/* Build SQL String with parameters */
SET #SQLQuery =
'SELECT ' + #column_name +
' FROM ' + #table_name
-- + ' WHERE clause if required'
/* Execute SQL */
EXECUTE(#SQLQuery)
Yes, this can be done using dynamic sql. Below are a couple of links to get you started:
http://www.codeproject.com/Articles/20815/Building-Dynamic-SQL-In-a-Stored-Procedure
http://www.mssqltips.com/sqlservertip/1160/execute-dynamic-sql-commands-in-sql-server/
You should also be aware of the potential dangers of using Dynamic sql.
Suppose I have many tables in my database. Every time I will insert data in any table. So, can I use a single stored procedure for all my data insertion in every table, instead of writing one stored procedure for each table?
In this scenario, each time I will pass table name and parameters dynamically to the stored procedure. If yes, can anyone give some basic idea how to perform this? If any extra information is required, please ask.
Thanks and regards,
Rizwan Gazi.
You could work with dynamic SQL and build the insert statement on the fly. THIS IS NOT RECOMMENDED but it should solve the problem you're asking about.
(I haven't run this code, but you can see what is being accomplished here with building the insert string and then executing it)
In this procedure, you pass in the table name, columns and values you care about and fire it off in a row based operation. With some minor tweaks you would be able to make it set based as well.
create procedure dbo.TableInsert
#tablename varchar(100)
, #columnlist varchar(max)
, #valueslist varchar(max)
as
begin
declare #sql varchar(max)
set #sql =
'insert into ' + #tablename
+ '(' + #columnlist + ')'
+ ' VALUES (' + #valueslist + ')'
print(#sql)
sp_executesql (#sql)
end
go
Execution would look something like this:
exec dbo.TableInsert
#tablename = 'TestTable'
, #columnlist = 'col1, col2, col3'
, #valuelist = '1,2,3'
Text insert would be a little trickier in this version since you have to wrap it around in single quotes.
exec dbo.TableInsert
#tablename = 'TestTable'
, #columnlist = 'col1, col2, col3'
, #valuelist = '''1'',''2'',''3'''
You could do something using dynamic SQL to build a query and then run it using:
EXEC SP_EXECUTESQL(#SQL)
(Assuming MS SQL Server)
Not sure I'd recommend it though and will probably be a total nightmare to test and maintain. Having different sprocs would be easier to test and maintain going forward and would perform better as the different sprocs would have separate query plans.
If you are working in code you could use a ORM to deal with basic CRUD stuff.
After some searching around i couldn't find a good answer that covers my issue.
I am working on the consolidation of around 100 databases. The structure is the same and they are all on the same server. All the databases have a table with login information.
We have created a core database with all the connection information from the other databases.
Now we need to create a view in the core database that contains all the login credentials from all the databases.
This means we need to use a loop to go through all the databases and select the user name and password.
Any ideas or suggestions are welcome
One possible solution is to create a stored procedure
DECLARE #sql varchar(max), #Database1 varchar(300)
set #Database1 = 'tempdb'
SET #sql='
USE '+#Database1+';
IF EXISTS (SELECT 1 FROM SYS.VIEWS WHERE NAME =''test_view'')
BEGIN
DROP VIEW test_view
PRINT ''VIEW EXISTS''
END'
PRINT #sql
EXEC(#sql)
declare #sql1 varchar(max)
// Modify below query as per your requirement its just for an idea
select #sql1 = IsNull(#sql1 + 'union all ','') +
'select * from ' + name + '.dbo.tblUser'
from sys.databases
where name like 'DbNamePrefix%'
set #sql1 = 'create view dbo.YourView as ' + #sql1
exec (#sql1)
Make a database job and schedule it as per your requirement.
To reference to your tables in the second database use this:
[DBName].[dbo].[TableName]
e.g.
CREATE VIEW [dbo].[ViewName]
as
select
a.ID,
a.Name,
b.Address
from TableA a
join SecondDBName.dbo.Table b
on ... ---Remaining code here...
NOTE: This will work only on the same server - if your databases are on different servers then you will need to create a linked server.
Take a look at this. Can this be one of the answers to your question?
http://blog.springsource.org/2007/01/23/dynamic-datasource-routing/
I am trying to write a database script (SQL Server 2008) which will copy information from database tables on one server to corresponding tables in another database on a different server.
I have read that the correct way to do this is to use a sql statement in a format similar to the following:
INSERT INTO <linked_server>.<database>.<owner>.<table_name> SELECT * FROM <linked_server>.<database>.<owner>.<table_name>
As there will be several tables being copied, I would like to declare variables at the top of the script to allow the user to specify the names of each server and database that are to be used. These could then be used throughout the script. However, I am not sure how to use the variable values in the actual SQL statements. What I want to achieve is something like the following:
DECLARE #SERVER_FROM AS NVARCHAR(50) = 'ServerFrom'
DECLARE #DATABASE_FROM AS NVARCHAR(50) = 'DatabaseTo'
DECLARE #SERVER_TO AS NVARCHAR(50) = 'ServerTo'
DECLARE #DATABASE_TO AS NVARCHAR(50) = 'DatabaseTo'
INSERT INTO #SERVER_TO.#DATABASE_TO.dbo.TableName SELECT * FROM #SERVER_FROM.#DATABASE_FROM.dbo.TableName
...
How should I use the # variables in this code in order for it to work correctly?
Additionally, do you think my method above is correct for what I am trying to achieve and should I be using NVARCHAR(50) as my variable type or something else?
Thanks
There is probably a better way to do this, but what you are probably trying to do in your example is what's called dynamic SQL where you treat the statement as a string and the execute it. This would be section #2 here:
http://www.mssqltips.com/tip.asp?tip=1160
There are some major downsides to dynamic SQL. You see a couple other approaches that might be better in that article.
If you want to execute a dynamically generated query then you have to use sp_ExecuteSQL
HTH
For the nvarchar(50) - you'd be better using sysname. This is a synonym in SQL Server (for nvarchar(128)) and represents the maximum length of an object identifier.
have a look at http://msdn.microsoft.com/en-us/library/ms188001.aspx - sp_executesql takes a parameter that is a string and executes the sql in that string. so you'd need to concatenate #SERVER_FROM and other params with the INSERT INTO part to make the entire sql statement, and then pass to sp_executesql.
nvarchar(50) is fine, unless your server/database names are longer than that :)
You can create the select statement by concatenating all the information together and then use sp_executesql
so:
sp_executesql 'INSERT INTO ' + #SERVER_TO + '.' + #DATABASE_TO +
'.dbo.TableName SELECT * FROM ' + #SERVER_FROM + '.' +
#DATABASE_FROM+'.dbo.TableName'
I like to make templates for dynamic SQL things like this - it's a lot easier to maintain complex statements and also sometimes easier to handle nested quotes - and definitely easier when terms need to be repeated in multiple places (like column lists):
DECLARE #sql AS nvarchar(max);
SET #sql = 'INSERT INTO {#SERVER_TO}.{#DATABASE_TO}.dbo.TableName
SELECT *
FROM {#SERVER_FROM}.{#DATABASE_FROM}.dbo.TableName'
SET #sql = REPLACE(#sql, '{#SERVER_TO}', QUOTENAME(#SERVER_TO))
SET #sql = REPLACE(#sql, '{#DATABASE_TO}', QUOTENAME(#DATABASE_TO))
SET #sql = REPLACE(#sql, '{#SERVER_FROM}', QUOTENAME(#SERVER_FROM))
SET #sql = REPLACE(#sql, '{#DATABASE_FROM}', QUOTENAME(#DATABASE_FROM))
EXEC(#sql)