Question

In a SSIS package at work there are some SQL tasks that create staging tables for holding import data. All the statements take this form:

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'dbo.tbNewTable') AND type in (N'U'))
BEGIN
    TRUNCATE TABLE dbo.tbNewTable
END
ELSE
BEGIN
    CREATE TABLE dbo.tbNewTable (
        ColumnA VARCHAR(10) NULL,
        ColumnB VARCHAR(10) NULL,
        ColumnC INT NULL
    ) ON PRIMARY
END

In Itzik Ben-Gan’s T-SQL Fundamentals I see a different form of statement for creating a table:

IF OBJECT_ID('dbo.tbNewTable', 'U') IS NOT NULL
BEGIN
    DROP TABLE dbo.tbNewTable
END

CREATE TABLE dbo.tbNewTable (
    ColumnA VARCHAR(10) NULL,
    ColumnB VARCHAR(10) NULL,
    ColumnC INT NULL
) ON PRIMARY

Each of these appears to do the same thing. After execution, there will be a empty table called tbNewTable in the dbo schema.

Are there any practical or theoretical differences between the two? What implications might they have?

Answer 1

The first one assumes that if the table exists, it has the same columns as those it would create. The second one does not make that assumption. So if a table with that name happened to exist and had a different set of columns, the two would have very different results.