Create date from day, month, year fields in MySQL

Question

Hello,

I am currently developing an application that displays documents and allows the members to search for these documents by a number of different parameters, one of them being date range.

The problem I am having is that the database schema was not developed by myself and the creator of the database has created a 'date' table with fields for 'day','month','year'.

I would like to know how I can select a specific day, month, year from the table and create a date object in SQL so that I can compare dates input by the user using BETWEEN.

Below is the structure of the date table:

CREATE TABLE IF NOT EXISTS `date` (
  `deposition_id` varchar(11) NOT NULL default '',
  `day` int(2) default NULL,
  `month` int(2) default NULL,
  `year` int(4) default NULL,
  PRIMARY KEY  (`deposition_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

Answer 1

Try to use CONCAT() and make it one field and compare .

Am not sure you can compare it as date after concatenation.

You can compare as integer.

concatinate year month day and make an integer like this 20101017 and compare.

Hopefully :)

Answer 2

You can use STR_TO_DATE() function.

Answer 3

To build a sortable date string from that, you'll need CONCAT to join the bits together and LPAD to make sure the month and day fields are two digits long. Something like this:

CONCAT(`year`,'-',LPAD(`month`,2,'00'),'-',LPAD(`day`,2,'00'))

Once you have that, you should be able to use BETWEEN, as they'll be in a sortable format. However if you still need to convert them to actual datetime fields, you can wrap the whole thing in UNIX_TIMESTAMP() to get a timestamp value.

So you'd end up with something like this:

SELECT UNIX_TIMESTAMP(CONCAT(`year`,'-',LPAD(`month`,2,'00'),'-',LPAD(`day`,2,'00'))) as u_date
WHERE u_date BETWEEN timestamp_1 and timestamp_2

However, be aware that this will be massively slower than if the field was just a simple timestamp in the first place. And you should definitely make sure you have an index on the year, month and day fields.