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Full Discussion: SQL datetime calculations
Top Forums Programming SQL datetime calculations Post 302352797 by figaro on Sunday 13th of September 2009 12:05:03 PM
Old 09-13-2009
SQL datetime calculations

Suppose I have a table as follows:
Code:
CREATE TABLE data ( `datetime` datetime DEFAULT NOT NULL, `temperature` float DEFAULT NO NULL );

populated with temperature samples of a couple times a second.

Let's say I want to find the temperatures which are 1 second apart:
Code:
SELECT D1.datetime, D2.datetime, D1.temperature, D2.temperature FROM data AS D1, data AS D2 WHERE D1.datetime - D2.datetime = 1;

And if I want to find the temperatures which are 1 minute apart:
Code:
SELECT D1.datetime, D2.datetime, D1.temperature, D2.temperature FROM data AS D1, data AS D2 WHERE D1.datetime - D2.datetime = 100;

What I dont understand is, why there is a multiplier of 100 and not 60, since there are only 60 seconds in a minute?
 

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SQL::Translator::Parser::PostgreSQL(3pm)		User Contributed Perl Documentation		  SQL::Translator::Parser::PostgreSQL(3pm)

NAME
SQL::Translator::Parser::PostgreSQL - parser for PostgreSQL SYNOPSIS
use SQL::Translator; use SQL::Translator::Parser::PostgreSQL; my $translator = SQL::Translator->new; $translator->parser("SQL::Translator::Parser::PostgreSQL"); DESCRIPTION
The grammar was started from the MySQL parsers. Here is the description from PostgreSQL: Table: (http://www.postgresql.org/docs/view.php?version=7.3&idoc=1&file=sql-createtable.html) CREATE [ [ LOCAL ] { TEMPORARY | TEMP } ] TABLE table_name ( { column_name data_type [ DEFAULT default_expr ] [ column_constraint [, ... ] ] | table_constraint } [, ... ] ) [ INHERITS ( parent_table [, ... ] ) ] [ WITH OIDS | WITHOUT OIDS ] where column_constraint is: [ CONSTRAINT constraint_name ] { NOT NULL | NULL | UNIQUE | PRIMARY KEY | CHECK (expression) | REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL ] [ ON DELETE action ] [ ON UPDATE action ] } [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] and table_constraint is: [ CONSTRAINT constraint_name ] { UNIQUE ( column_name [, ... ] ) | PRIMARY KEY ( column_name [, ... ] ) | CHECK ( expression ) | FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ] [ MATCH FULL | MATCH PARTIAL ] [ ON DELETE action ] [ ON UPDATE action ] } [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] Index: (http://www.postgresql.org/docs/view.php?version=7.3&idoc=1&file=sql-createindex.html) CREATE [ UNIQUE ] INDEX index_name ON table [ USING acc_method ] ( column [ ops_name ] [, ...] ) [ WHERE predicate ] CREATE [ UNIQUE ] INDEX index_name ON table [ USING acc_method ] ( func_name( column [, ... ]) [ ops_name ] ) [ WHERE predicate ] Alter table: ALTER TABLE [ ONLY ] table [ * ] ADD [ COLUMN ] column type [ column_constraint [ ... ] ] ALTER TABLE [ ONLY ] table [ * ] ALTER [ COLUMN ] column { SET DEFAULT value | DROP DEFAULT } ALTER TABLE [ ONLY ] table [ * ] ALTER [ COLUMN ] column SET STATISTICS integer ALTER TABLE [ ONLY ] table [ * ] RENAME [ COLUMN ] column TO newcolumn ALTER TABLE table RENAME TO new_table ALTER TABLE table ADD table_constraint_definition ALTER TABLE [ ONLY ] table DROP CONSTRAINT constraint { RESTRICT | CASCADE } ALTER TABLE table OWNER TO new_owner View table: CREATE [ OR REPLACE ] VIEW view [ ( column name list ) ] AS SELECT query AUTHORS
Ken Y. Clark <kclark@cpan.org>, Allen Day <allenday@ucla.edu>. SEE ALSO
perl(1), Parse::RecDescent. perl v5.14.2 2012-05-01 SQL::Translator::Parser::PostgreSQL(3pm)
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