SQL Server 2008 R2和SQL Server 2014中的TRUNCATE TABLE的名称解析

Question

We experienced an error in our code that was executed in SQL Server 2014 which we do not encounter in SQL Server 2008 R2.

Our code is like this:

IF EXISTS (
SELECT 1
FROM master.dbo.sysdatabases
WHERE name = N'WebDB'
)
BEGIN
    TRUNCATE TABLE [WebDB].[dbo].[webtable] 
END

The Truncate Table command will only execute if the WebDB exists. In SQL Server 2008 R2, this code runs without any problems. In SQL Server 2014, there is a problem that when the WebDB doesn't exist, it will throw an error saying that 'Database 'WebDB' does not exist.'. It is doing name resolution of the TRUNCATE TABLE command prior to the actual execution.

Can someone explain this change in behaviour for SQL Server 2014?

Answer 1

The SQL Editor parses the code without any error but in runtime the SQL Engine throws error

I cannot explain the reason for change in behaviour but you can convert your sample code into dynamic SQL and execute with sp_executeSQL command as follows

IF EXISTS (
    SELECT * FROM master.dbo.sysdatabases WHERE name = N'WebDB'
)
BEGIN
    declare @sql nvarchar(100) = N'TRUNCATE TABLE [WebDB].[dbo].[webtable]'
    exec sp_executeSql @sql
END

Answer 2

Actually the problem is because the existence of the database is evaluated when parsing the script, before running it. All statements are parsed independently of the condition for their execution.

This is something which was not being done in SQL 2008.

Anyway you can update your query as following.

IF EXISTS (
SELECT 1
FROM master.dbo.sysdatabases
WHERE [name] = N'WebDB'
)
BEGIN
    DECLARE @T NVARCHAR(1000)
    SET @T = N'TRUNCATE TABLE [WebDB].[dbo].[webtable]'
    EXECUTE SP_EXECUTESQL @T 

END

This is not the SSMS behavior, this change has been done in the core, even if you run your query using SQLCMD you will observe the same behavior.