• gkodinov/kgeorge@macbook.gmz's avatar
    BUG#25575: ERROR 1052 (Column in from clause is ambiguous) with sub-join · 16d2d682
    gkodinov/kgeorge@macbook.gmz authored
     Two problems here:
    
     Problem 1:
    
     While constructing the join columns list the optimizer does as follows:
      1. Sets the join_using_fields/natural_join members of the right JOIN 
       operand.
      2. Makes a "table reference" (TABLE_LIST) to parent the two tables.
      3. Assigns the join_using_fields/is_natural_join of the wrapper table
       using join_using_fields/natural_join of the rightmost table
      4. Sets join_using_fields to NULL for the right JOIN operand.
      5. Passes the parent table up to the same procedure on the upper 
       level.
    
     Step 1 overrides the the join_using_fields that are set for a nested 
     join wrapping table in step 4.
     Fixed by making a designated variable SELECT_LEX::prev_join_using to 
     pass the data from step 1 to step 4 without destroying the wrapping 
     table data.
    
     Problem 2:
    
     The optimizer checks for ambiguous columns while transforming 
     NATURAL JOIN/JOIN USING to JOIN ON. While doing that there was no
     distinction between columns that are used in the generated join
     condition (where ambiguity can be checked) and the other columns
     (where ambiguity can be checked only when resolving references
     coming from outside the JOIN construct itself).
     Fixed by allowing the non-USING columns to be present in multiple 
     copies in both sides of the join and moving the ambiguity check 
     to the place where unqualified references to the join columns are
     resolved (find_field_in_natural_join()).
    16d2d682
join_nested.test 27.9 KB