Is it possible to use a set of query results for column names in a select statement?
Example, I have a table named TableA:
Column: Type:
KeyOne nvarchar(5)
KeyTwo nvarchar(5)
TableB is another table, whose column names might be stored in TableA.
Suppose TableB is like this:
Column: Type:
Val1 int
Val2 int
Is there any way I could do a query like this to get the columns?
SELECT (select TOP 1 KeyOne, KeyTwo FROM TableA)
FROM TableB
Another example using strings would be like this:
SELECT (select 'Val1', 'Val2')
FROM TableB
Is this possible in any way without concatenated SQL?
Unfortunately you can only do this with dynamic SQL, but it's pretty straightforward:
DECLARE #cols VARCHAR(MAX) = (SELECT TOP 1 KeyOne+','+KeyTwo FROM TableA)
,#sql VARCHAR(MAX)
SET #sql = 'SELECT '+#cols+' FROM TableB'
EXEC (#sql)
You can read table column names dynamically from sys.columns system views or using other management views
select name from sys.columns where object_id = object_id(N'TableName')
Then by creating a dynamic SQL query you can create your own select
Related
Prerequisite : all the tables are dynamic so i cant use the column names
I have two tables
Candidate table :
Table which has all columns and data required to be selected
DataDictionary :
Table where i have only those columns which are to be selected for querying
Now what i want to do is select only that data and columns from the candidate table which are present in datadictionary and skip those that data and column which are not present in datadictionary
what i have tried is
SELECT ColumnName
INTO #Candidate
FROM DataDictionaryDetail WHERE DataDictionaryId =1
select *
from candidate
where NOT EXISTS (select *from #Candidate)
but this brings only columns but not data
I need a proper way to select data also and columns
You need dynamic SQL for this
DECLARE #sql nvarchar(max) = N'
SELECT
'
+ (
SELECT STRING_AGG(QUOTENAME(ColumnName), ',')
FROM DataDictionaryDetail
WHERE DataDictionaryId = 1
) + N'
from candidate;
';
EXEC sp_executesql #sql;
I am trying to select all distinct values from all tables that start with a specific name, like: 'logs_2020_12_01', 'logs_2021_01_02', ..To select all tables with this specific name is straight forward:
SELECT name FROM sqlite_master WHERE type='table' AND name LIKE 'logs_%';
The select I want for one individual table is:
SELECT DISTINCT batch FROM logs_2021_01_27;
but I cannot find a way to combine it to make the selection from all tables. I tried a couple of things but it does not work, like:
SELECT DISTINCT batch FROM (SELECT name FROM sqlite_master WHERE type='table' AND name LIKE 'logs_%')
any ideas?
thanks
What about using Dynamic SQL, stored your tables information into a temp table with id column and set it to identity.
CREATE TABLE #temp ---identity column will be used to iterate
(
id INT IDENTITY,
TableName VARCHAR(20)
)
INSERT INTO #temp
SELECT name FROM sqlite_master WHERE type='table' AND name LIKE 'logs_%';
-- choose your own results with where conditions
DECLARE #SQL VARCHAR(MAX)
DECLARE #Count INT = 1
DECLARE #Table VARCHAR(20)
WHILE #COUNT <= (SELECT COUNT(*) FROM #temp)
BEGIN
select #table = TABLENAME FROM #temp WHERE id = #Count
SELECT #sql = 'SELECT DISTINCT(batch) FROM '+ #table
PRINT #SQL
SET #Count = #Count + 1
END
after your print result looks good, change it to EXEC(#SQL), thanks
SQLite does not support dynamic sql.
You have to select the column batch from each of all the tables and combine them with UNION so the duplicates are removed:
SELECT batch FROM logs_2020_12_01 UNION
SELECT batch FROM logs_2020_12_02 UNION
......................................
SELECT batch FROM logs_2020_12_30 UNION
SELECT batch FROM logs_2020_12_31
If you don't know the full names of the tables, you can get them with this statement:
SELECT name
FROM sqlite_master
WHERE type = 'table' AND name LIKE 'logs/_%' ESCAPE '/'
and then use a programming language to construct a SELECT statement with UNION to get the results that you want.
I need to create table from the return schema of sql query. Here, sql query has multiple joins.
Example - In below scenario, create table schema for column 'r' & 't'.
select a.x as r b.y as t
from a
JOIN b
ON a.m = b.m
I can not use 'select into statement' because I get an input sql select statement and need to copy the output of that query to destination table at runtime.
If I'm reading your problem correctly, you're getting SQL from an external source and you want to run that into a table (maybe with data, maybe without). This should do:
use tempdb;
declare #userSuppliedSQL nvarchar(max) = N'select top 10 * from Util.dbo.Numbers';
declare #sql nvarchar(max);
set #sql = concat('
with cte as (
', #userSuppliedSQL, '
)
select *
into dbo.temptable
from cte
where 9=0 --delete this line if you actually want data
;');
print #sql
exec sp_executesql #sql;
select * from dbo.temptable;
This assumes that the supplied query is legal for use as the body of a common table expression (e.g. all columns are named and unique). Note that you can't select into a temp table (i.e. #temp) because the temp table only exists for the duration of the sp_executesql call.
Also, for the love of all that is holy, please understand that by running arbitrary SQL that a user passes in, that you're opening yourself up to SQL injection.
I know you said you cannot select into, but can you select into with 0=1 to create an empty table structure and then insert after that?
select a.x as r b.y as t
into TABLE
from a
JOIN b
ON a.m = b.m
where 0 = 1
Use the into clause here. Like
Select col1, col2, col3
into newtable
from old table;
select a.x as r b.y as t
into c
from a
JOIN b ON a.m = b.m
I am trying to figure out the best method to insert column names held in Table1 into a SELECT statement running against Table2. This query is running in a stored procedure. That doesn't do a very good job of explaining, so lets say I had these values in Table1:
What I am trying to do is use these column names in the SELECT statement against Table2:
Select -- Column Names
from Table2
where UserId = 3;
I'm not sure if an input parameter could be used in that way or how to pass the values into it. For example:
Select #ColumnNames
from Table2
where UserId = 3;
Or maybe a join to table 2?
Thanks!
You will have to use Dynamic SQL
declare #columns varchar(1000)
declare #sql varchar(8000)
select #columns='', #sql=''
select #columns=#columns+value+',' from table1
set #columns=left(#columns,len(#columns)-1)
set #sql='select '+#columns+' from table2'
exec(#sql)
But beware of SQL Injection and read www.sommarskog.se/dynamic_sql.html
You could query the system tables to get the column(s) i.e. (take out WHERE clause to see all the tables and columns)
SELECT tab.name AS TableName,
col.name AS ColName,
tp.name AS SType,
col.max_length,
col.[precision],
(CASE col.is_nullable
WHEN 1 THEN 'true'
WHEN 0 THEN 'false'
ELSE 'unknown'
END) AS Is_Nullable
FROM sys.tables as tab
LEFT OUTER JOIN sys.columns AS col
ON tab.object_id = col.object_id
LEFT OUTER JOIN sys.types AS tp
ON col.system_type_id = tp.system_type_id
WHERE tab.name = 'Table1'
ORDER BY tab.name,col.name
I have a DataBase with around +100 tables, like half of tables have column A & column B.
My question is, Can I query all tables that have this columns with a specific values e.g.
SELECT * FROM DATABASE
WHERE
EACHTABLE HAS COLUMN A = 21 //only if table has columns and then values
AND
COLUMN B = 13
I am not sure how exact I will do it, nothing is coming up on google either
You can use the undocumented MS stored procedure sp_MSforeachtable, if you fancy living life recklessly:
create table T1 (
ColumnA int not null,
ColumnB int not null
)
go
create table T2 (
ColumnA int not null,
Column2 int not null
)
go
create table T3 (
Column1 int not null,
ColumnB int not null
)
go
create table T4 (
ColumnA int not null,
ColumnB int not null
)
go
insert into T1 values (1,2);
insert into T2 values (3,4);
insert into T3 values (5,6);
insert into T4 values (7,8);
go
create table #Results (TableName sysname,ColumnA int,ColumnB int)
exec sp_MSforeachtable 'insert into #Results select ''?'',ColumnA,ColumnB from ?',
#whereand = ' and syso.object_id in (select object_id from sys.columns where name=''ColumnA'') and syso.object_id in (select object_id from sys.columns where name=''ColumnB'')'
select * from #Results
drop table #Results
Result:
TableName ColumnA ColumnB
------------------------------------- ----------- -----------
[dbo].[T1] 1 2
[dbo].[T4] 7 8
By default, sp_MSforeachtable will, as its name implies, perform the same task for each table in the database. However, one optional parameter to this procedure, called #Whereand, can be used to modify the WHERE clause of the internal query that enumerates the tables in the database. It helps to know that this internal query has already established two aliases to some of the system views. o is an alias for sysobjects (the legacy system view). syso is an alias for sys.all_objects (a more modern system view).
Once sp_MSforeachtable has decided which tables to run against, it will execute the query given to it as its first parameter. But, it will replace ? with the schema and table name (? is the default replacement character. This can be changed as needed)
In this case, I chose to create a temp table, then have each selected table store its results into this temp table, and after sp_MSforeachtable has finished running, to select the combined results out with no further processing.
There is a similar (and similarly undocumented) procedure called sp_MSforeachdb which will access each user database on the server. These can even be combined (although you have to be careful with doubling up ' quote characters twice, at times). However, there's no equivalent sp_MSforeachcolumn.
Try this:
select t.name from sys.objects t inner join sys.columns c
on t.name=OBJECT_NAME(c.object_id)
where t.type='U'
and c.name in('col1','col2')
group by t.name
having COUNT(*) = 2
order by 1
Then you just loop through all the tables and fine the values for these columns.
Like
Declare #out TABLE(tblname varchar(100))
if exists(select * from tbl1 where col1='21' and col2='22')
BEGIN
INSERT INTO #out
select tbl1
END
You can try like this using dynamic query.
select 'select * from '+table_name+ ' where'+column_name+'=21'
from information_schema.columns where column_name = 'A'
I suggest to use two steps:
First, find out all tables in your database that have these two columns and use it for a temporal derived table. For I am not an expert in SQL-Server 2008 I recommend to have a look at the whitepages.
The expression might look like this:
SELECT tablename
FROM information_schema.tables sdbt
WHERE "column a" IN
(SELECT columns
FROM information_schema.columns col
WHERE col.tablename = sdbt.tablename)
Second, use a expresssion to filter the results according to your demanded values.
This command should do the trick in one go, only for column A, amend accordingly to include any other columns you need:
exec sp_MSforeachtable
#command1=N'SELECT * FROM ? WHERE A = 21',
#whereand=' and o.name IN (SELECT TABLE_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE COLUMN_NAME = ''A'') '