TABLESAMPLE must be immedidately after a table name.

The WHERE clause in the following SQL query runs after TABLESAMPLE.

 SELECT 
     *
 FROM 
     table_name 
 TABLESAMPLE (10 PERCENT) 
 WHERE 
     id = 1

If you want to run a WHERE

union relies on column order rather than column names. This is the same as in SQL. For columns that the type don't match, the super type is used. However, this is really dangerous if you are careful. It is suggested that you define a function call unionByName to hanle this.