ISDATE() equivalent for MySQL

Question

I have a line of code for SQL server which takes a date listed as \"YYYYMMDD\" where the DD is 00 and converts the 00 to 01 so that it works with datetime. I would like to

Answer 1

You can try using the STR_TO_DATE function. It returns null if the expression is not date, time, or datetime.

WHERE STR_TO_DATE(dt, '%d,%m,%Y') IS NOT NULL

Answer 2

Similar to Timo Kähkönen's answer, I've used TIMESTAMPDIFF to determine if a date is valid like ISDATE does. I use the same date in both date parameters. It returns zero if it a date, NULL if not.

I ran all three examples with BENCHMARK with valid and invalid dates. I ran this on a shared server from the ISP JustHost, MYSQL version 5.6.32-78.1:

SELECT benchmark(10000000, DAYNAME('2016-06-21 18:17:47'));
-- 1 row(s) returned   3.215 sec / 0.0000072 sec

Mine:  Query took 3.5333 seconds.

SELECT benchmark(10000000, STR_TO_DATE('2016-06-21 18:17:47', '%d,%m,%Y'));
-- 1 row(s) returned   7.905 sec / 0.0000081 sec

Mine: Query took 7.9635 seconds.

SELECT benchmark(10000000, TIMESTAMPDIFF(DAY,'2016-06-21 18:17:47','2016-06-21 18:17:47'));

Mine:  Query took 5.1373 seconds.

...........................

With bad date (June 41st?)

SELECT benchmark(10000000, DAYNAME('2016-06-41 18:17:47'));

Mine: Query took 7.3872 seconds.

SELECT benchmark(10000000, STR_TO_DATE('2016-06-41 18:17:47', '%d,%m,%Y'));

Mine: Query took 7.9919 seconds.

SELECT benchmark(10000000, TIMESTAMPDIFF(DAY,'2016-06-41 18:17:47','2016-06-41 18:17:47'));

Mine:  Query took 7.3792 seconds.

STR_TO_DATE is slightly slower than the other two. The DAYNAME method seems the fastest if you are working mostly with valid dates. But none is truly a bad way to go.

Answer 3

One possibility, that allows argument to be string, integer or date:

WHERE DAYNAME(dt) IS NOT NULL

These valid dates return 'Tuesday':

SELECT IFNULL(DAYNAME('2016-06-21 18:17:47') , '');
SELECT IFNULL(DAYNAME('2016-06-21') , '');

These invalid dates return '' (empty string):

SELECT IFNULL(DAYNAME('0000-00-00 00:00:00') , '');
SELECT IFNULL(DAYNAME('2016-06-32 18:17:47') , '');
SELECT IFNULL(DAYNAME(NULL) , '');
SELECT IFNULL(DAYNAME(10) , '');

It seems that DAYNAME is 2x faster in mysql 5.6 than STR_TO_DATE:

SELECT benchmark(10000000, DAYNAME('2016-06-21 18:17:47'))
1 row(s) returned   3.215 sec / 0.0000072 sec

SELECT benchmark(10000000, STR_TO_DATE('2016-06-21 18:17:47', '%d,%m,%Y'))
1 row(s) returned   7.905 sec / 0.0000081 sec

And I suppose that if the argument is date (rather than eg. string), the performance is better.

Answer 4

Well, while I appreciate all statements, I always like it the easy way.

All date stamps either have the "-" or "/" characters in them, so why not check all date columns that have such characters, using the LIKE argument.

SELECT * FROM TABLE WHERE DATE_COLUMN LIKE '%/%';
SELECT * FROM TABLE WHERE DATE_COLUMN LIKE '%-%';

Answer 5

You could also use the following

Using a REGEXP '^([1-9]|0[1-9]|1[012])/([1-9]|0[1-9]|[12][0-9]|3[01])/(19|20)[0-9][0-9]'

But regexp can be tricky here though, as there too many different format for a date,

Or

Cast DATE and then check for length of result, found null, then not date. length(DATE(mydate))