Snowflake does not document its Virtual Column capability that uses the AS clause. I am doing a migration and needing to filter out virtual columns programatically.
Is there any way to identify that a column is virtual? The Information Schema.COLLUMNS view shows nothing different between a virtual and non-virtual column definition.
There is a difference between column defined as DEFAULT and VIRTUAL COLUMN(aka computed, generated column):
Virtual column
CREATE OR REPLACE TABLE T1(i INT, calc INT AS (i*i));
INSERT INTO T1(i) VALUES (2),(3),(4);
SELECT * FROM T1;
When using AS (expression) syntax the expression is not visible inCOLUMN_DEFAULT:
DEFAULT Expression
In case of the defintion DEFAULT (expression):
CREATE OR REPLACE TABLE T2(i INT, calc INT DEFAULT (i*i));
INSERT INTO T2(i) VALUES (2),(3),(4);
SELECT * FROM T2;
It is visible in COLUMN_DEFAULT:
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'T2';
Comparing side-by-side with SHOW COLUMNS:
SHOW COLUMNS LIKE 'CALC';
-- kind: VIRTUAL_COLUMN
One notable difference between them is that virtual column cannot be updated:
UPDATE T1
SET calc = 1;
-- Virtual column 'CALC' is invalid target.
UPDATE T2
SET calc = 1;
-- success
How about using SHOW COLUMNS ? you should identify them when expression
field is not null.
create table foo (id bigint, derived bigint as (id * 10));
insert into foo (id) values (1), (2), (3);
SHOW COLUMNS IN TABLE foo;
SELECT "table_name", "column_name", "expression" FROM table(result_scan(last_query_id()));
| table_name | column_name | expression |
| ---------- | ----------- | -------------- |
| FOO | ID | null |
| FOO | DERIVED | ID*10 |
I normally use the desc table option.
First lets create the table with some example data:
create or replace temporary table ColumnTypesTest (
id int identity(1,1) primary key,
userName varchar(30),
insert_DT datetime default CAST(CONVERT_TIMEZONE('UTC', CAST(CURRENT_TIMESTAMP() AS TIMESTAMP_TZ(9))) AS TIMESTAMP_NTZ(9)) not null,
nextDayAfterInsert datetime as dateadd(dd,1,insert_DT)
);
insert into ColumnTypesTest (userName) values
('John'),
('Cris'),
('Anne');
select * from ColumnTypesTest;
ID
USERNAME
INSERT_DT
NEXTDAYAFTERINSERT
1
John
2021-10-04 19:11:21.069
2021-10-05 19:11:21.069
2
Cris
2021-10-04 19:11:21.069
2021-10-05 19:11:21.069
3
Anne
2021-10-04 19:11:21.069
2021-10-05 19:11:21.069
Now the answer to your question
Using the 'desc table <table_name>;' you will get a column named kind which will tell you if it is virtual or not, also separately there is the default with NULL if it has no default value.
name
type
kind
null?
default
primary key
unique key
check
expression
comment
policy name
ID
NUMBER(38,0)
COLUMN
N
IDENTITY START 1 INCREMENT 1
Y
N
USERNAME
VARCHAR(30)
COLUMN
Y
N
N
INSERT_DT
TIMESTAMP_NTZ(9)
COLUMN
N
CAST(CONVERT_TIMEZONE('UTC', CAST(CURRENT_TIMESTAMP() AS TIMESTAMP_TZ(9))) AS TIMESTAMP_NTZ(9))
N
N
NEXTDAYAFTERINSERT
TIMESTAMP_NTZ(9)
VIRTUAL
Y
N
N
DATE_ADDDAYSTOTIMESTAMP(1, INSERT_DT)
A/
With 'desc table <table_name>' you get meta data of the table with a column named kind, which will say VIRTUAL or COLUMN. In case it is VIRTUAL, then in the column expression you get how that column is calculated.
This is used in Stored Procedures, and saved in an array of arrays with javascript, from there the next query in the stored procedure is created dynamically. A while loop is used to go through the resultSet and push each row intho the array of arrays. You can then use javascript filter to just get the virtual columns. This is part of the advantage of having a mix of javascript and SQL in Snowflake Stored Procedures.
Here the documentation which doesn't say much.
Related
I have a table that looks like this:
ActivityID
Time Used
Activity Type
Activity Category ID
Activity Category
123456
30
A
1
X
765432
120
B
2
Y
876462
65
C
3
Z
h52635
76
D
3
Z
hsgs62
187
E
1
X
I would like to use the Activity Category as parameter (#ActivityCategory) to filter my report later, it means the filter should be X;Y;Z.
When I choose one Activity Category, the sum of "Time used" should appear.
My question is: how should I build the query, to be able to group the activities with the same Activity Category together and use the Category XYZ as a parameter?
Something like this perhaps:
-- Sample data
DECLARE #table TABLE (ActivityId INT, TimeUsed INT, ActivityCategory CHAR(1));
INSERT #table VALUES(123,20,'X'), (129,50,'Y'), (254,30,'Y'), (991,10,'Z');
-- Parameter
DECLARE #ActivityCategory VARCHAR(100) = 'X,Y';
SELECT t.ActivityCategory, TimeUsed = SUM(t.TimeUsed)
FROM #table AS t
CROSS APPLY STRING_SPLIT(#ActivityCategory,',') AS s -- You will need a string splitter funciton
WHERE t.ActivityCategory = s.value
GROUP BY t.ActivityCategory;
Returns:
ActivityCategory TimeUsed
---------------- -----------
X 20
Y 80
Alan's answer is good, but I'd personally use a temp table and a join for performance reasons. The table being queried might be very large, in which case a join to a temp table would be more performant than CROSS APPLY.
The easiest way to pass multi-value parameters in and out of your query are comma-separated lists. Indeed if you are using Report Server / SSRS then that is how the "Multiple Value" box in the user interface will deliver the users' selections into a varchar parameter.
--Declare and set parameter
DECLARE #ActivityCategories varchar(MAX)
SET #ActivityCategories = 'X,Y,Z'
--Convert individual parameter values to a temp table
DROP TABLE IF EXISTS #ParamaterValues
CREATE TABLE #ParameterValues (ActivityCategory varchar(10) NOT NULL PRIMARY KEY CLUSTERED)
INSERT INTO #ParameterValues WITH(TABLOCK)
SELECT value
FROM STRING_SPLIT(#ActivityCategories,',')
GROUP BY value
ORDER BY value
--Join on temp table to filter by paramater values
SELECT ActivityID,
TimeUsed,
ActivityType,
ActivityCategoryID,
ActivityCategory
FROM dbo.YourTable a
INNER JOIN #ParameterValues b ON a.ActivityCategory = b.ActivityCategory
I have a table with ID column
ID column is like this : IDxxxxyyy
x will be 0 to 9
I have to select row with ID like ID0xxx% to ID3xxx%, there will be around 4000 ID with % wildcard from ID0000% to ID3999%.
It is like combining LIKE with IN
Select * from TABLE where ID in (ID0000%,ID0001%,...,ID3999%)
I cannot figure out how to select with this condition.
If you have any idea, please help.
Thank you so much!
You can use pattern matching with LIKE. e.g.
WHERE ID LIKE 'ID[0-3][0-9][0-9][0-9]%'
Will match an string that:
Starts with ID (ID)
Then has a third character that is a number between 0 and 3 [0-3]
Then has 3 further numbers ([0-9][0-9][0-9])
This is not likely to perform well at all. If it is not too late to alter your table design, I would separate out the components of your Identifier and store them separately, then use a computed column to store your full id e.g.
CREATE TABLE T
(
NumericID INT NOT NULL,
YYY CHAR(3) NOT NULL, -- Or whatever type makes up yyy in your ID
FullID AS CONCAT('ID', FORMAT(NumericID, '0000'), YYY),
CONSTRAINT PK_T__NumericID_YYY PRIMARY KEY (NumericID, YYY)
);
Then your query is a simple as:
SELECT FullID
FROM T
WHERE NumericID >= 0
AND NumericID < 4000;
This is significantly easier to read and write, and will be significantly faster too.
This should do that, it will get all the IDs that start with IDx, with x that goes form 0 to 4
Select * from TABLE where ID LIKE 'ID[0-4]%'
You can try :
Select * from TABLE where id like 'ID[0-3][0-9]%[a-zA-Z]';
I have a table which I have cut down into basic fields, it is called Customer
ID | Name | Type
1 | Smith | 2
I want to create a trigger on INSERT that will change the value of the inserting Type, into a number example:
INSERT INTO Customer (Name,Type) VALUES ('Jones', 'Recommended')
The Type field should be a number and it is set as an INT column. I do not want to change this away from INT.
How can I force the word Recommended to be changed to ‘0’ a zero?
In Theory :
This is the trigger :
ALTER TRIGGER [dbo].[CustomersInsert] ON [dbo].[Customer]
INSTEAD OF INSERT
AS BEGIN
INSERT Into Customer (Name,Type)
SELECT
inserted.[Name],
Isnull([Types].Id, 0)
FROM inserted
Left Join [dbo].[Types] on inserted.[Type] = [Types].Caption
END
The [dbo].[Types] is for keep Types.
But in real :
You can't execute INSERT INTO Customer (Name,Type) VALUES ('Jones', 'Recommended')
because Type is INT and 'Recommended' is not.
In a table A i have a column (varchar*30) city-id with the value e.g. 1,2,3 or 2,4.
The description of the value is stored in another table B, e.g.
1 Amsterdam
2 The Hague
3 Maastricht
4 Rotterdam
How must i join table A with table B to get the descriptions in one or maybe more rows?
Assuming this is what you meant:
Table A:
id
-------
1
2
3
Table B:
id | Place
-----------
1 | Amsterdam
2 | The Hague
3 | Maastricht
4 | Rotterdam
Keep id column in both tables as auto increment, and PK.
Then just do a simple inner join.
select * from A inner join B on (A.id = B.id);
Ideal way to deal with such scenarios is to have a normalized table as Collin. In case that can't be done here is the way to go about -
You would need to use a table-valued function to split the comma-seperated value. If you are having SQL-Server 2016, there is a built-in SPLIT_STRING function, if not you would need to create one as shown in this link.
create table dbo.sCity(
CityId varchar(30)
);
create table dbo.sCityDescription(
CityId int
,CityDescription varchar(30)
);
insert into dbo.sCity values
('1,2,3')
,('2,4');
insert into dbo.sCityDescription values
(1,'Amsterdam')
,(2,'The Hague')
,(3,'Maastricht')
,(4,'Rotterdam');
select ctds.CityDescription
,sst.Value as 'CityId'
from dbo.sCity ct
cross apply dbo.SplitString(CityId,',') sst
join dbo.sCityDescription ctds
on sst.Value = ctds.CityId;
I have this function:
CREATE FUNCTION [dbo].[full_ads](#date SMALLDATETIME)
returns TABLE
AS
RETURN
SELECT *,
COALESCE((SELECT TOP 1 ptype
FROM special_ads
WHERE [adid] = a.id
AND #date BETWEEN starts AND ends), 1) AS ptype,
(SELECT TOP 1 name
FROM cities
WHERE id = a.cid) AS city,
(SELECT TOP 1 name
FROM provinces
WHERE id = (SELECT pid
FROM cities
WHERE id = a.cid)) AS province,
(SELECT TOP 1 name
FROM models
WHERE id = a.mid) AS model,
(SELECT TOP 1 name
FROM car_names
WHERE id = (SELECT car_id
FROM models
WHERE id = a.mid)) AS brand,
(SELECT TOP 1 pid
FROM cities
WHERE id = a.cid) pid,
(SELECT TOP 1 car_id
FROM models
WHERE id = a.mid) bid,
(SELECT TOP 1 name
FROM colors
WHERE id = a.color_id) AS color,
COALESCE((SELECT TOP 1 fileid
FROM carimgs
WHERE adid = a.id), 'nocarimage.png') AS [image]
FROM ads a
WHERE isdeleted <> 1
Sometimes it works correctly, but sometimes column names doesn't match values like (I have written a sample results with fewer columns just to show the problem):
ID Name City Color Image
----------------------------------------------
1 John New York Null Red
2 Ted Chicago Null Blue
As you see color and Image values are shifted one column and this continues to the last column.
Can anyone tell me where the problem is?
This arises from using *.
If the definition of ads changes (columns added or removed) this can mess up the metadata associated with the TVF.
You would need to run sp_refreshsqlmodule on it to refresh this metadata after such changes. It is best to avoid * in view definitions or inline TVFs for this reason.
An example of this
CREATE TABLE T
(
A CHAR(1) CONSTRAINT DF_A DEFAULT 'A',
B CHAR(1) CONSTRAINT DF_B DEFAULT 'B',
C CHAR(1) CONSTRAINT DF_C DEFAULT 'C',
D CHAR(1) CONSTRAINT DF_D DEFAULT 'D'
)
GO
INSERT INTO T DEFAULT VALUES
GO
CREATE FUNCTION F()
RETURNS TABLE
AS
RETURN
SELECT * FROM T
GO
SELECT * FROM F()
GO
ALTER TABLE T DROP CONSTRAINT DF_C, COLUMN C
ALTER TABLE T ADD E CHAR(1) DEFAULT 'E' WITH VALUES
GO
SELECT * FROM F()
Returns
+---+---+---+---+
| A | B | C | D |
+---+---+---+---+
| A | B | D | E |
+---+---+---+---+
Note that the D and E values are shown in the wrong columns. It still shows column C even though it has been dropped.