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authortpearson <tpearson@283d02a7-25f6-0310-bc7c-ecb5cbfe19da>2010-01-20 01:29:50 +0000
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+-----------------------
+KEXI ALTER TABLE ISSUES
+-----------------------
+
+1. PROBLEMS
+- different databases have different set of altering capabilities
+ (SQLite has no table altering capabilities at all; re-creation is needed:
+ this has high cost in time and disk space for large tables)
+- we need to collect every detailed change made in Table Designer and apply
+ these changes to existing table schema
+- in the case when a table is already filled with data, we need to perform
+ tasks to move that data to a new structure,
+ especially if database engine can't do it for us or if the engine
+ wants simply drop the data because convertion cannot be done automatically
+- because of above issues, some work needs to be done at the client side
+
+2. What can be altered using ALTER TABLE:
+2.1 Inserting columns
+ (into a specified position)
+ ADD COLUMN <column_definition> [FIRST | AFTER <col_name> ]
+
+ (adding many colums at the end)
+ ADD COLUMN <column_definition>,...
+
+2.2 Adding constraints, indices
+ ADD INDEX [<index_name>] [<index_type>] (<index_col_name>,...)
+
+ ADD CONSTRAINT [<symbol>] PRIMARY KEY [<index_type>] (<index_col_name>,...)
+
+ ADD CONSTRAINT [<symbol>] UNIQUE [<index_name>] [<index_type>] (<index_col_name>,...)
+
+ ADD CONSTRAINT [<symbol>] FOREIGN KEY [<index_name>] (<index_col_name>,...)
+ [<reference_definition>]
+
+2.3 Altering column properties
+ ALTER COLUMN <col_name> {SET DEFAULT <literal> | DROP DEFAULT}
+
+ CHANGE COLUMN <old_col_name> column_definition [FIRST|AFTER <col_name>]
+
+ (rename column)
+ CHANGE <old_column> <new_column>
+
+ MODIFY COLUMN <column_definition> [FIRST | AFTER <col_name>]
+
+2.4 Dropping
+ DROP COLUMN <col_name>
+
+ DROP PRIMARY KEY
+
+ DROP INDEX <index_name>
+
+ DROP FOREIGN KEY <fk_symbol>
+
+2.5 Renaming a table
+ RENAME TO <new_tbl_name>
+
+
+3. How to perform table altering be re-creation:
+SQLite: (taken from Ticket 236: Add RENAME TABLE
+ - will be easier to work around missing ALTER TABLE
+ http://www.sqlite.org/cvstrac/tktview?tn=236,8)
+ Currently the recommended method to ALTER TABLE is:
+
+ 1. Create a temporary table.
+ 2. Copy all data from original table to temporary table.
+ 3. Drop the original table.
+ 4. Create a new table.
+ 5. Copy all data from the temporary table to the new table.
+
+For example, suppose you have a table named "t1" with columns
+names "a", "b", and "c" and that you want to delete column "c"
+from this table. The following steps illustrate how this could be done:
+
+BEGIN TRANSACTION;
+CREATE TEMPORARY TABLE t1_backup(a,b);
+INSERT INTO t1_backup SELECT a,b FROM t1;
+DROP TABLE t1;
+CREATE TABLE t1(a,b);
+INSERT INTO t1 SELECT a,b FROM t1_backup;
+DROP TABLE t1_backup;
+COMMIT;
+
+If the table name also changes on altering, it's easier to do the
+altering (no temp. table needed):
+
+BEGIN TRANSACTION;
+CREATE TABLE t2(c,d);
+INSERT INTO t2 (c,d) SELECT a,b FROM t1;
+DROP TABLE t1;
+COMMIT;
+
+ If we had RENAME TABLE, we'd get easier alter table here:
+ 1. Rename original table to temp name.
+ 2. Create new table with ORIGINAL name.
+ 3. Move data from previous to new table.
+ 4. Drop previous table.
+
+4. PROPOSED ALGORITHM
+
+
+
+5. Useful documentation
+ http://dev.mysql.com/doc/mysql/en/ALTER_TABLE.html
+
+
+6. Document History
+2004-07-20 js
+ Started
+ Asked Richard Hipp about RENAME TABLE
+