The new IDENTITY column is filled with auto-incremented numbers from its attached SEQUENCE automatically if not targeted in the INSERT statement. recreate all indexes and constraints on new tableĭROP TABLE sample_old - after making sure , ticker text - use your actual data typesĪLTER TABLE sample ADD PRIMARY KEY (index) Index integer GENERATED ALWAYS AS IDENTITY drop all indexes and constraints on old table to free up names Note that columns can only be removed if they do not have any indexes that rely on them. If you are going to write a new table, do that instead of all you are showing above.Īny internal references to the old table have to be dropped and recreated. The DROP COLUMN clause can be used to remove a column from a table. Typically a problem for DBs with concurrent access. The first option might be even cheaper overall, though more invasive. Or UPDATE the existing column in place, which is slghtly tricky in the presence of a UNIQUE or PRIMARY KEY constraint (while doable).Įither is expensive (for big tables) and blocking. You need to recreate the table to get the desired order of columns. The SET DATA TYPE and TYPE are equivalent. Third, supply the new data type for the column after the TYPE keyword. Second, specify the name of the column that you want to change the data type after the ALTER COLUMN clause. New columns are added at the end of the column list with ALTER TABLE. First, specify the name of the table to which the column you want to change after the ALTER TABLE keywords. Never rely on the physical table layout because, as you've discovered, it can change.ĭatabases are inherently share Entities and you never know who is going to be doing what in (or to?) them. Įvery single SELECT statement you write should specify the columns that it wants, in the order it wants them. The amount of work that the database has to do to make such changes grows exponentially with every new referring table and all the rows in them). Also, as soon as you have Foreign Keys referencing these Primary Keys, the database really should prevent you from doing this (and no "cascading" changes is not the answer. If you have any kind of processing that relies on something being "ordered", do not rely on the Primary Key to provide it.Ĭan you imagine the chaos if your Bank renumbered people's Checking Accounts every time someone else closed their account? It's a very, very Bad Idea. Primary Key fields are intended to be unique, not sequential.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |