How can I get the number of columns returned by an SQL query using SQL Server?
For example, if I have a query like following:
SELECT *
FROM A1, A2
It should return the total number of columns in table A1 + total number of columns in table A2. But the query might be more complicated.
Here is one method:
select top 0
into _MYLOCALTEMPTABLE
from (your query here) t
select count(*)
from Information_Schema.Columns c
where table_name = '_MYLOCALTEMPTABLE'
You can do something similar by creating a view.
You didn't specify your SQL Server version but I'm assuming it's not 2012. However, future readers of this question might be on 2012+ so I'm posting this answer for them.
SQL Server 2012 provides a set of procedures to provide more meta-data about queries and parameters. In this case, the stored procedure sp_describe_first_result_set will provide a handy tabular form.
There is also a DMO function, sys.dm_exec_describe_first_result_set, to provide similar content which is what you'd want to use in your example
DECLARE
-- Your query goes here
#query nvarchar(4000) = N'SELECT * FROM mdm.tblStgBatch AS TSB';
-- Tabular results
EXECUTE sys.sp_describe_first_result_set #tsql = #query;
-- Simple column count
SELECT
COUNT(1) AS column_count
FROM
sys.dm_exec_describe_first_result_set(#query, NULL, 0);
The new metadata discovery options are replacing FMTONLY which is how one would solve this problem prior to 2012. My TSQL chops are apparently not strong enough to do anything useful with it and instead I'd have to bail out to a .NET language to work with the output of FMTONLY.
SET FMTONLY ON;
SELECT *
FROM A1, A2;
SET FMTONLY OFF;
Try this;
--Insert into a temp table (this could be any query)
SELECT *
INTO #temp
FROM [yourTable]
--Select from temp table
SELECT * FROM #temp
--List of columns
SELECT COUNT(name) NumOfColumns FROM tempdb.sys.columns WHERE object_id =
object_id('tempdb..#temp');
--drop temp table
DROP TABLE #temp
Ugly I know:
SELECT COUNT(*) +
(
SELECT COUNT(*)
FROM information_schema.columns
WHERE table_name = 'A1'
)
FROM information_schema.columns
WHERE table_name = 'A2'
Related
I have a scenario where I need to execute queries on different tables using ETL tool.
I want to store all the required queries in control table.
As part of this, I want to include the column WatermarkValue as part of the value in the column Source_Query, so that I can dynamically use it for my execution. This is how my control table should look like.
Table Name: Metadata_Table
TableID
Source_Query
WatermarkValue
1
select * from dbo.cust_eventchanges where lastmodifieddate >{WatermarkValue}
2022-10-09T12:00:00
2
select * from dbo.cust_contacts where lastmodifieddate >{WatermarkValue}
2022-07-08T03:20:00
So when I run my metadata table like this
select * from Metadata_Table where TableID=1
the result should be like below.
select * from dbo.cust_eventchanges where lastmodifieddate >'2022-10-09T12:00:00'
I know we can do this by concatenating two columns. But I would like to know if this is achievable.
I couldn't able to figure out how to achieve this. Hence, I need help on this scenario
Using sp_executesql with a typed parameter definition reduces the risk of SQL Injection
Example below shows how to run one of your queries. You could simply wrap this in a cursor where each iteration executes a different query in the metadata table.
DROP TABLE IF EXISTS #MetaData_Table
GO
CREATE TABLE #MetaData_Table
(TableID INT,Source_Query NVARCHAR(MAX),WatermarkValue DATETIME)
INSERT INTO #MetaData_Table
(TableID,Source_Query,WatermarkValue)
VALUES
(1,'select * from dbo.cust_eventchanges where lastmodifieddate >#WatermarkValue','2022-10-09T12:00:00'),
(2,'select * from dbo.cust_contacts where lastmodifieddate >#WatermarkValue','2022-07-08T03:20:00')
SELECT * FROM #MetaData_Table
DECLARE #dtVariable DATETIME;
DECLARE #SQLString NVARCHAR(500);
DECLARE #ParmDefinition NVARCHAR(500);
-- You can put this in a cursor to loop through all your tables, this is hardcoded to one for simplicity.
SELECT #SQLString = Source_Query, #dtVariable = WatermarkValue FROM #MetaData_Table WHERE TableID = 1
SET #ParmDefinition = N'#WatermarkValue DATETIME'
EXECUTE sp_executesql #SQLString, #ParmDefinition,
#WatermarkValue = #dtVariable;
You can create a view and use a view in your ETL tool instead of the table.
create view vMetadataQueries
as
select TableID, Source_Query + WatermarkValue as [ExecuteQuery]
from Metadata_Table
This is not a particularly good way of doing that because it potentially leaves you open to SQL injection.
Say, I have 100 columns in a table. I do not know in which columns a particular value could exist. So, I would like to check across all columns, if it exists in any of the 100 columns, I would like to select it.
I searched around a bit, and in most places the solution seems to be something like the following
select *
from tablename
where col1='myval'
or col2='myval'
or col3='myval'
or .. or col100='myval'
I also read a few forums where having to do this is said to be a bad case of database design, I agree, but I'm working on an already existing table in a database.
Is there a more intelligent way to do this?
One way is by reversing the In operator
select *
from yourtable
where 'Myval' in (col1,col2,col3,...)
If you don't want to manually type the columns use dynamic sql to generate the query
declare #sql varchar(max)='select *
from yourtable
where ''Myval'' in ('
select #sql+=quotename(column_name)+',' from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME='yourtable'
select #sql =left(#sql,len(#sql)-1)+')'
--print #sql
exec sp_executesql #sql
This is my first time posting on SO, so please go easy!
I'm attempting to write a SQL script that queries the same table for a list of databases in a single SQL Server instance.
I have successfully queried the list of databases that I required using the following, and inserting this data into a temp table.
Select name Into #Versions
From sys.databases
Where name Like 'Master%'
Master is suffixed with numerical values to identify different environments.
Select * From #Versions
Drop Table #Versions
The table name I am trying to query, is the same in each of the databases, and I want to extract the newest value from this table and insert it into the temp table for each of the database names returned.
I have tried researching this but to no avail. I am fairly comfy with SQL but I fear I could be out of my depth here.
You can do the following. Once you have the list of your databases, you can build up the query (you need to edit it for your purpose).
Select name Into #Versions
From sys.databases
Where name Like 'test%'
declare #sql as varchar(max) = ''
select #sql = #sql + 'INSERT INTO sometable SELECT TOP 1 * FROM ' + name + '..sourcetable ORDER BY somedate DESC; '
FROM #Versions
exec (#sql)
Drop Table #Versions
Look at The undocumented sp_MSforeachdb procedure and here
I want a program to access a table/view/stored procedure, etc. (something materialized, let's call it X) that abstracts the real location of the data contained in three basic tables (the tables have the same definition in all locations).
I would want X to fetch the server name, catalog name and table name from somewhere (a table, probably) and access the specific three basic tables. The caller of X would not know which specific tables were being called.
How can I do this in SQL Server (2008)?
Like a function, a view can't use dynamic SQL - it can't go find some metadata reference somewhere and adjust accordingly.
I think the closest thing to what you want is a synonym. Let's say you have three different databases, A, B and C. In A the table you want the view to reference is dbo.foo, in B it is dbo.bar, and in Cit is dbo.splunge. So then you could create a synonym like so in each database:
USE A;
GO
CREATE SYNONYM dbo.YourCommonViewName FOR dbo.foo;
GO
USE B;
GO
CREATE SYNONYM dbo.YourCommonViewName FOR dbo.bar;
GO
USE C;
GO
CREATE SYNONYM dbo.YourCommonViewName FOR dbo.splunge;
GO
Now this technically isn't a view, but in each database you can say...
SELECT <cols> FROM dbo.YourCommonViewName;
...and it will return the data from the database-specific table.
To do this in a stored procedure would be much simpler. Say you store the server, database and table name in some table, e.g. dbo.lookup:
CREATE TABLE dbo.lookup
(
id INT PRIMARY KEY,
[server] SYSNAME,
[database] SYSNAME,
[table] SYSNAME,
active BIT NOT NULL DEFAULT (0)
);
-- you may want a constraint or trigger to ensure
-- only one row can be active at any one time.
INSERT dbo.lookup(id, [server], [database], [table])
SELECT 1,N'serverA',N'databaseA',N'tableA'
UNION ALL SELECT 2,N'serverB',N'databaseB',N'tableB';
Now your program can say:
UPDATE dbo.lookup SET active = 1 WHERE ... ?
And your stored procedure can be:
CREATE PROCEDURE dbo.whatever
AS
BEGIN
SET NOCOUNT ON;
DECLARE #sql NVARCHAR(MAX);
SELECT #sql = N'SELECT <cols> FROM ' + QUOTENAME([server])
+ '.' + QUOTENAME([database]) + '.dbo.' + QUOTENAME([table])
FROM dbo.lookup WHERE active = 1;
EXEC sp_executesql #sql;
END
GO
I still don't understand the point, and I don't know what you're planning to do when two different users expect to call your program at the same time, and they each should get results from a different location.
Agreed with Aaron on the fact that views and functions cannot use dynamic sql.
Still what you can do is build a clr table valued function. In that you can play with .net code and query whatever you want. And build you data accordingly and output what you need.
So instead of querying the data like
select * from myview
you can query it
select * from dbo.clr_mymockupview()
Create SYNONYMs to your remote servers.
Create your VIEW to concatenate your locations together using UNION ALL.
Since you said "tables", join your tables before the UNION ALL and hopefully, MS will perform the JOIN remotely.
Use a union query with parameters for database, server, and catalog:
Select col1, col2, <etc.>, 'table1' as tablename, 'server1' as servername, 'catalog1' as catname from server1.catalog1.table1
Union Select col1, col2, <etc.>, 'table2' as tablename, 'server2' as servername, 'catalog2' as catname from server2.catalog2.table2
Union Select col1, col2, <etc.>, 'table3' as tablename, 'server3' as servername, 'catalog3' as catname from server3.catalog3.table3
Then filter based on your 3 criteria. This probably won't be blazing fast but will wonk with std. SQL.
I have a question addressed to sql guru.
There are two tables with almost identical structure.
Based on parameter passed into the stored procedure I need to collect data from one or another table.
How to do that in a best way?
Please do not suggest to combine those tables into single one - that is not appropriate.
I did it following (MS SQL Server 2008):
Select *
FROM
String s
JOIN (
SELECT id
,TypeCode
,ProdNo
FROM Table1
WHERE #param = 1 AND TypeCode= 'INV'
UNION
SELECT id
,TypeCode
,ProdNo
FROM Table2
WHERE #param = 2 AND TypeCode= 'INV'
) m ON m.Id = s.Id
WHERE s.Id = 256
but when I looked at execution plan I was surprised because it got data from both tables in parallel threads and only after that filtered by #param value.
I thought that filtering will be made on the first stage and data collected from single table.
Is there a way to make select only from one table without splitting query into two queries and using IF operator?
Thanks
you really need to read this Dynamic Search Conditions in T-SQL by Erland Sommarskog. You shouldn't worry about repeating code, this is not some homework assignment. Just worry about making the execution plan use an index. When making SQL code "pretty" the only thing to consider is indenting & case, any other changes can cause the query plan to be slower. I've seen trivial changes to a super fast query result in a super slow query. GO FOR SPEED (index usage) and duplicate code as necessary. also see: The Curse and Blessings of Dynamic SQL
You tagged the question sql-server-2008, so if you're running SQL 2008 SP1 CU5 (10.0.2746) and SQL 2008 R2 CU1 (10.50.1702) and later, there is a new behavior (as explained in the "Dynamic Search Conditions" article linked above) of OPTION(RECOMPILE) that does not appear in all versions of SQL 2008 or in 2005. This behavior basically evaluates the #Local_Variables values at runtime and recompiles the query accordingly. In your case, this should cause one half of your UNION to be eliminated when compiling them.
Could you just use a simple IF statement?
IF #Param = 1
BEGIN
EXEC SQL
END
ELSE IF #Param = 2
BEGIN
EXEC SQL
END
ELSE
RAISERROR('Invalid Parameter', 16, 1)
Or alternatively you could build the query dynamically and execute it using the sp_executesql stored procedure.
DECLARE #Sql NVARCHAR(100)
SET #Sql = N'SELECT * FROM ('
IF #Param = 1
SET #Sql = #Sql + N'SELECT 1 a, 2 b, 3 c'
ELSE IF #param = 2
SET #Sql = #Sql + N'SELECT 4 a, 5 b, 6 c'
ELSE
RAISERROR('Invalid Parameter', 16, 1)
SET #Sql = #Sql + ') tbl'
EXEC sp_executesql #sql
First thing I'd suggest is putting the ID filter inside the union as well.
I've also changed the UNION to UNION ALL. This avoids evaluating DISTINCT rows
Select *
FROM
String s
JOIN (
SELECT id
,TypeCode
,ProdNo
FROM Table1
WHERE #param = 1 AND TypeCode= 'INV' AND id = 256
UNION ALL
SELECT id
,TypeCode
,ProdNo
FROM Table2
WHERE #param = 2 AND TypeCode= 'INV' AND id = 256
) m ON m.Id = s.Id
WHERE s.Id = 256
SQL Server's not that clever - when writing queries you should only ensure that you send the least amount of SQL to get the data you want (without sending superfluous statements), but also provide the most amount of information (via filters) where possible to give the query optimiser as many hints as possible about the data. As you've seen, it will execute all the SQL you send it.
So it sounds like you need to use dynamic-SQL from what I'm reading. This also gives you the benefit of being able to merge common parts of the SQL cutting down on the amount of duplication. For example, you could have (just taking your inner code -- you can wrap the rest of your stuff around it):
DECLARE #sql NVARCHAR(1000)
SET #sql = 'SELECT id, TypeCode, ProdCode'
IF #param = 1
SET #sql = #sql + ' FROM table1'
IF #param = 2
SET #sql = #sql + ' FROM table2'
SET #sql = #sql + ' WHERE TypeCode = ''INV'''
EXECUTE sp_ExecuteSQL #sql
Just be aware, if you're going to wind this into something more complicated, about little Bobby Tables: it's possible to abuse sp_ExecuteSQL and open gaping holes, but used correctly - with parameterised dynamic SQL - it's as good as a stored procedure.
if you can create a tDUMMY table (with a single dummy row) give this a shot.
Select
*
FROM
String s
JOIN (
SELECT
id, TypeCode, ProdNo
FROM
tDUMMY INNER JOIN Table1 ON TypeCode= 'INV'
WHERE
#param = 1
UNION ALL
SELECT
id, TypeCode, ProdNo
FROM
tDUMMY INNER JOIN Table2 ON TypeCode= 'INV'
WHERE
#param = 2
) m ON m.Id = s.Id
WHERE s.Id = 256
theoretically the query optimizer should first filter the tDUMMY table and then attempt the join. So if #param = 1 the second query should get out much faster (it will check 1 row of tDUMMY again, but it shouldn't check table2)
Note - i also made it UNION ALL (but it wouldn't have much of an impact) because one side will always return no rows anyway.