Why is it not good practice to use date values with two-digits years in MySQL?



As we know that, YEAR(2) stores a year in 2-digit format. For example, we can write 69 to store 1969 as a year. In YEAR (2), the year can be specified from 1970 to 2069 (70 to 69).

MySQL interprets 2-digit year values with the help of following rules −

  • Year values in the range 00-69 are converted to 2000-2069.
  •  Year values in the range 70-99 are converted to 1970-1999.

We must not store date values as a 2-digit format because values stored in this format becomes vague as the century is unknown.

It can be understood more clearly with the help of following MySQL example −

mysql> Create Table year_test(val year(2));
Query OK, 0 rows affected, 1 warning (0.23 sec)

mysql> insert into year_test(val) values('70');
Query OK, 1 row affected (0.14 sec)

mysql> insert into year_test(val) values('00');
Query OK, 1 row affected (0.06 sec)

mysql> select * from year_test;
+-----+
| val |
+-----+
| 70  |
| 00  |
+-----+
2 rows in set (0.00 sec)

mysql> select * from year_test where val = '1970';
+-----+
| val |
+-----+
| 70  |
+-----+
1 row in set (0.03 sec)

mysql> select * from year_test where val = '2000';
+-----+
| val |
+-----+
| 00  |
+-----+
1 row in set (0.00 sec)

mysql> select * from year_test where val = '1900';
Empty set (0.06 sec)

It is uncertain that with which year we connote, ‘1900’ or ‘2000’, by storing 00 to ‘val’. MySQL is interpreting it as the year 2000.


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