Contents of query probing data

Each record is identified by a statement ID. A record contains:

• The database name the user was connected to
• A list of tables, identified by their table id (tabid)
• A list of columns for each table, identified by their column number (colno)
• A list of references between each pair of tables, also known as the join descriptors
• A list of column pairs for each join descriptor, also known as the join predicates

A join predicate in the probing data corresponds to an equality join predicate between columns of different tables in the query. For example:

 table_1.col_a = table_2.col_x

A join descriptor is comprised of:

• All of the join predicates of the same pair of tables. For example:

  table_1.col_a = table_2.col_x and 
  table_1.col_b = table_2.col_y and 
  table_1.col_c = table_2.col_z

• The type of the join - an inner join or left outer join.
• Information about any unique indexes on the dimension table of the join. The dimension table is the right table in case of a left outer join. The unique index must be on the complete set of columns contained in this join descriptor.