Commits on Aug 2, 2017

1. sql: re-vamp the view dependency analysis …

   Prior to this patch, view dependency analysis during CREATE VIEW was
   broken because it would only check dependencies after plan
   optimization, i.e. possibly after some dependency were lost. For
   example, with the queries:
   
   ```sql
   CREATE VIEW v AS SELECT k FROM (SELECT k,v FROM kv) -- loses dependency on kv.v
   CREATE VIEW v AS SELECT k,v FROM kv WHERE FALSE -- loses dependency on kv
   ```
   
   This patch addresses the issue as follows:
   
   - the dependencies are now collected during the initial construction
     of the query plan, before any optimization are applied. This way we
     ensure the dependency tracking is complete.
   - a migration is implemented that will fix any view descriptor and
     corresponding dependency information that was populated prior to
     this fix.

   

   knz committed Aug 2, 2017
   Configuration menu

   • View commit details
   • Copy full SHA for 83f873c
   • Browse repository at this point

   Copy the full SHA

   83f873c View commit details

   Browse the repository at this point in the history

2. sql: make view descriptors depend on table/columns by IDs …

   This patch does what it says on the label: the descriptor still
   contains a valid SQL query, but with all table names rewritten to use
   numeric table references. These are hidden initially, until
   the referenced tables gets a new schema.
   
   For example:
   ```
    CREATE TABLE kv(k INT PRIMARY KEY, v INT);
    CREATE VIEW vx AS SELECT v AS x FROM kv;
    SHOW CREATE VIEW vx;
    +------+-----------------------------------------+
    | View |           CreateView                    |
    +------+-----------------------------------------+
    | vx   | CREATE VIEW vx AS SELECT v AS x FROM kv |
    +------+-----------------------------------------+
    (1 row)
    ALTER TABLE kv ADD COLUMN d INT;
    SHOW CREATE VIEW vx;
    +------+--------------------------------------------------------------+
    | View |                          CreateView                          |
    +------+--------------------------------------------------------------+
    | vx   | CREATE VIEW vx AS SELECT v AS x FROM [64(1, 2) AS kv (k, v)] |
    +------+--------------------------------------------------------------+
    (1 row)
   ```
   
   A side effect of this patch is that view definitions can now use star
   expansion, i.e. `CREATE VIEW kv_alias AS SELECT * FROM kv` is now
   possible and valid. (And there was much rejoicing.)
   
   Another side effect, visible in the example above, is that `SHOW
   CREATE VIEW` now reveals the structural dependency (showing both the
   ID and the original table name) when the table's name or column
   definitions change.
   
   This may or may not be desirable from a UX perspective, however anyone
   wishing to improve upon this will take note that if the column list in
   the table descriptor was altered after the view was created (e.g. to
   add new columns, rename columns or remove columns not depended on by
   the view), there is no valid way to print out the view definition
   using valid SQL but without using the table reference syntax. Consider
   the example above: suppose column "v" was renamed to "w"; trying to
   print out as `create view vx as select v as x from kv` would be
   invalid because then column "v" would have disappeared; then suppose
   "v" was renamed to "w" and a new unrelated column "v" was added,
   trying `create view vx as select v as x from kv as kv(v)` would be
   invalid as well because the new column `v` is unrelated to the one the
   view was intended to depend on. Due to these obstacles, it is
   advisable to let the numeric table reference show up in the output of
   `SHOW CREATE VIEW` and document this behavior.
   
   Although it would be correct to do so for newly-created clusters, this
   patch does *not* lift the restriction on ALTER that prevents it from
   renaming tables or columns depended on by views. This change would be
   correct on new clusters because once the guarantee is enforced that
   all view descriptors depend on table/columns by IDs, renaming becomes
   possible (renaming preserves the ID); however, for previously created
   clusters there may exist already some view descriptors containing
   by-name table references, and allowing those to be renamed would be
   unsound. The proper approach is to completement this patch by a
   cluster migration which rewrites all existing view descriptors. This
   work is left to a subsequent commit.
   
   A last improvement brought by this PR is that column renames are now
   properly visible in pg_catalog:
   
   ```sql
   > CREATE VIEW v (x) AS SELECT k FROM kv
   > SELECT definition FROM pg_catalog.pg_views WHERE viewname = 'v'
   SELECT k AS x FROM (SELECT k FROM kv)
   ```

   

   knz committed Aug 2, 2017
   Configuration menu

   • View commit details
   • Copy full SHA for ba28022
   • Browse repository at this point

   Copy the full SHA

   ba28022 View commit details

   Browse the repository at this point in the history