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| author | Jordan Lewis <jordanthelewis@gmail.com> | 2017-01-19 15:29:17 -0500 |
|---|---|---|
| committer | Jordan Lewis <jordanthelewis@gmail.com> | 2017-01-30 11:27:04 -0500 |
| commit | f9c6cbd55c56de7994b74630acd141c324411719 (patch) | |
| tree | 714d0b6a3dd14b3e765cfda634fb6987ce4809ed /activerecord | |
| parent | d5651436d64c1a3f0b95910cb66c13bb29229f46 (diff) | |
| download | rails-f9c6cbd55c56de7994b74630acd141c324411719.tar.gz rails-f9c6cbd55c56de7994b74630acd141c324411719.tar.bz2 rails-f9c6cbd55c56de7994b74630acd141c324411719.zip | |
Simplify Postgres query for column_definitions()
column_definitions() needs to fetch the collation for every column, if
present. Previously, it did so using a correlated subquery - a subquery
that references results from the outer scope.
This patch updates the query to remove the subquery in favor of a
simpler and more efficient JOIN clause.
Running the two queries through EXPLAIN against Postgres additionally
shows that the original form with a correlated subquery requires a
Nested Loop Left Join, while the new form with a simple JOIN can use a
more efficient Merge Left Join.
Diffstat (limited to 'activerecord')
| -rw-r--r-- | activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb index 0ebd907cc0..315d70c33f 100644 --- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb +++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb @@ -759,11 +759,11 @@ module ActiveRecord query(<<-end_sql, "SCHEMA") SELECT a.attname, format_type(a.atttypid, a.atttypmod), pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod, - (SELECT c.collname FROM pg_collation c, pg_type t - WHERE c.oid = a.attcollation AND t.oid = a.atttypid AND a.attcollation <> t.typcollation), - col_description(a.attrelid, a.attnum) AS comment - FROM pg_attribute a LEFT JOIN pg_attrdef d - ON a.attrelid = d.adrelid AND a.attnum = d.adnum + c.collname, col_description(a.attrelid, a.attnum) AS comment + FROM pg_attribute a + LEFT JOIN pg_attrdef d ON a.attrelid = d.adrelid AND a.attnum = d.adnum + LEFT JOIN pg_type t ON a.atttypid = t.oid + LEFT JOIN pg_collation c ON a.attcollation = c.oid AND a.attcollation <> t.typcollation WHERE a.attrelid = #{quote(quote_table_name(table_name))}::regclass AND a.attnum > 0 AND NOT a.attisdropped ORDER BY a.attnum |