Re: delete column

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От Jochem van Dieten
Тема Re: delete column
Дата
Msg-id 3CCABF98.3080600@oli.tudelft.nl
обсуждение исходный текст
Ответ на Re: delete column  (Bruce Momjian <pgman@candle.pha.pa.us>)
Список pgsql-general
[retry with correct address]

Bruce Momjian wrote:
 >
 > FAQ updated to take advantage of rollback-able DROP TABLE:
 >
 >     BEGIN;
 >     LOCK TABLE old_table;
 >     SELECT ...  -- select all columns but the one you want to remove
 >     INTO TABLE new_table
 >     FROM old_table;
 >     DROP TABLE old_table;
 >     ALTER TABLE new_table RENAME TO old_table;
 >     COMMIT;

Depending on the dataset and the dominant query types I frequently add
an ORDER BY clause to force a sort on the data as it resides on the
disk. Not very usefull for datasets that change a lot, but it can help
for some queries.

      BEGIN;
      LOCK TABLE old_table;
      SELECT ...  -- select all columns but the one you want to remove
      INTO TABLE new_table
      FROM old_table
      ORDER BY dominant_column;
      DROP TABLE old_table;
      ALTER TABLE new_table RENAME TO old_table;
      COMMIT;

Jochem


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