Came across a problem relating to temp table column alias used within a subquery. What it boils down to is I can reference a column name which doesn't exist within the temp table used in the subquery, and the outer query returns ALL rows regardless of the erroneous predicate. This may be to do with the window function used within the temp table because I haven't been able to reproduce the problem by simply renaming/aliasing an existing column.
My prod server at work is SQL 2012 but I've just tested on my SQL 2016 developer install at home and the issue is still present.
I will provide sample SQL below. Please don't read too much into *what* I'm trying to do - all I've done is create a vastly simplified version of the data I'm working with just to make this easier to explain:
--Create database
USE MASTER;
IF EXISTS (SELECT name
FROM master.dbo.sysdatabases
WHERE name = 'DB1')
BEGIN
DROP DATABASE DB1
END;
CREATE DATABASE DB1
GO
USE DB1;
--Create and populate table
CREATE TABLE dbo.People (
ID INT IDENTITY,
PersonName VARCHAR(20),
Gender CHAR(1),
DoB DATE);
INSERT dbo.People
(PersonName, Gender, DoB)
VALUES ('Bob','M', '1-Jun-1981'),
('Dave','M', '1-jul-1981'),
('Tim','M','1-aug-1981'),
('Jenny','F','1-sep-1981'),
('Becky','F','1-oct-1981'),
('Sarah','F','1-nov-1981');
--Create and populate temp table
--This determines the max DoB for males and females
IF OBJECT_ID('tempdb..#tmp') IS NOT NULL
BEGIN
DROP TABLE #tmp
END;
SELECT DISTINCT Gender, MAX(DoB) OVER (PARTITION BY Gender) AS maxdob
INTO #tmp
FROM dbo.People;
--Now here are the queries
--The first query should produce an error because there is no column called DoB in #tmp table
--Verify by running the subquery on it's own
--Instead it returns ALL rows from the table (could be embarrassing if the subquery is used as part of a DELETE statement)
SELECT * FROM dbo.People
WHERE DoB IN (SELECT DoB FROM #tmp);
--The second query works exactly as expected
SELECT * FROM dbo.People
WHERE DoB IN (SELECT maxdob FROM #tmp);
My question - is my assumption correct that the first query should produce an error message? Or is there something I'm missing?
↧
