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Full Discussion: SQL: copying data down
Top Forums Programming SQL: copying data down Post 302578076 by radoulov on Wednesday 30th of November 2011 05:09:36 PM
Old 11-30-2011
If you need to improve the performance of the above statement you may try to index the date column
(in certain cases, for example Oracle (not sure for MySQL, you may check wit explain <your_statement_here>),
may try to use the index in order to avoid the costly sorting operation -
because the optimizer is aware that the data in the index is already sorted).

BTW: thanks for providing the necessary code in order to set up a test case!

Last edited by radoulov; 11-30-2011 at 06:39 PM..
 

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ALTER 
INDEX(7) SQL Commands ALTER INDEX(7) NAME
ALTER INDEX - change the definition of an index SYNOPSIS
ALTER INDEX name RENAME TO new_name ALTER INDEX name SET TABLESPACE tablespace_name ALTER INDEX name SET ( storage_parameter = value [, ... ] ) ALTER INDEX name RESET ( storage_parameter [, ... ] ) DESCRIPTION
ALTER INDEX changes the definition of an existing index. There are several subforms: RENAME The RENAME form changes the name of the index. There is no effect on the stored data. SET TABLESPACE This form changes the index's tablespace to the specified tablespace and moves the data file(s) associated with the index to the new tablespace. See also CREATE TABLESPACE [create_tablespace(7)]. SET ( storage_parameter = value [, ... ] ) This form changes one or more index-method-specific storage parameters for the index. See CREATE INDEX [create_index(7)] for details on the available parameters. Note that the index contents will not be modified immediately by this command; depending on the parame- ter you might need to rebuild the index with REINDEX [reindex(7)] to get the desired effects. RESET ( storage_parameter [, ... ] ) This form resets one or more index-method-specific storage parameters to their defaults. As with SET, a REINDEX might be needed to update the index entirely. PARAMETERS
name The name (possibly schema-qualified) of an existing index to alter. new_name The new name for the index. tablespace_name The tablespace to which the index will be moved. storage_parameter The name of an index-method-specific storage parameter. value The new value for an index-method-specific storage parameter. This might be a number or a word depending on the parameter. NOTES
These operations are also possible using ALTER TABLE [alter_table(7)]. ALTER INDEX is in fact just an alias for the forms of ALTER TABLE that apply to indexes. There was formerly an ALTER INDEX OWNER variant, but this is now ignored (with a warning). An index cannot have an owner different from its table's owner. Changing the table's owner automatically changes the index as well. Changing any part of a system catalog index is not permitted. EXAMPLES
To rename an existing index: ALTER INDEX distributors RENAME TO suppliers; To move an index to a different tablespace: ALTER INDEX distributors SET TABLESPACE fasttablespace; To change an index's fill factor (assuming that the index method supports it): ALTER INDEX distributors SET (fillfactor = 75); REINDEX INDEX distributors; COMPATIBILITY
ALTER INDEX is a PostgreSQL extension. SEE ALSO
CREATE INDEX [create_index(7)], REINDEX [reindex(7)] SQL - Language Statements 2010-05-14 ALTER INDEX(7)
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