Time and Date

Storing Times and Dates

You can use a string literal to store a time value or a date value. When you do this, the literal is implicitly converted to the time or date. For example, if the table t contains a column dt of type DATETIME, you can use the following statement to store the literal.

INSERT INTO t(dt) VALUES ('2020-11-21');

Alternatively, you can use the TO_Date and Time Functions, such as TO_DATE and TO_TIMESTAMPto explicitly convert a string literal to a time value or a date value.

Inserting or Updating a Column With the Current Timestamp

To allow inserts or updates of a TIMESTAMP, TIMESTAMP(6), DATETIME , or a DATETIME(6) column with the current timestamp, define the column with the clause:

• DEFAULT <timefunction>, to insert a column with the current timestamp.

• ON UPDATE <timefunction>, to update a column with the current timestamp.

• DEFAULT <timefunction> ON UPDATE <timefunction>, to insert and update a column with the current timestamp.

where <timefunction> is one of the following values: NOW(), NOW(6), CURRENT_TIMESTAMP(), CURRENT_TIMESTAMP(6).

CREATE TABLE s(id INT, ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP());
INSERT INTO s(id) VALUES(1);

SELECT * FROM s;

+------+---------------------+
| id   | ts                  |
+------+---------------------+
|    1 | 2020-05-21 09:12:25 | 
+------+---------------------+

CREATE TABLE s1(id INT, ts DATETIME(6) ON UPDATE CURRENT_TIMESTAMP(6));
INSERT INTO s1(id,ts) VALUES(1,"2017-07-01");

SELECT * FROM s1;

+------+----------------------------+
| id   | ts                         |
+------+----------------------------+
|    1 | 2017-07-01 00:00:00.000000 |
+------+----------------------------+

UPDATE s1 SET id = 2 WHERE id = 1;

SELECT * FROM s1;

+------+----------------------------+
| id   | ts                         |
+------+----------------------------+
|    2 | 2020-05-21 09:36:47.124979 |
+------+----------------------------+

CREATE TABLE s2(id INT, ts DATETIME(6) DEFAULT NOW(6) ON UPDATE NOW(6));
INSERT INTO s2(id) VALUES(1);
INSERT INTO s2(id) VALUES(2);

SELECT * FROM s2;

+------+----------------------------+
| id   | ts                         |
+------+----------------------------+
|    2 | 2020-05-21 11:21:30.998275 |
|    1 | 2020-05-21 11:21:30.992868 |
+------+----------------------------+

UPDATE s2 SET id = 2 WHERE id = 1;

SELECT * FROM s2;

+------+----------------------------+
| id   | ts                         |
+------+----------------------------+
|    2 | 2020-05-21 11:21:30.998275 |
|    2 | 2020-05-21 11:23:39.134793 |
+------+----------------------------+

CREATE TABLE r(d DATETIME(6), ts TIMESTAMP(6), id INT);
INSERT r(d, id) VALUES("2017-07-01", 1);

SELECT * FROM r;

+----------------------------+----------------------------+------+
| d                          | ts                         | id   |
+----------------------------+----------------------------+------+
| 2017-07-01 00:00:00.000000 | NULL                       |    1 |
+----------------------------+----------------------------+------+

UPDATE r SET id = 2 WHERE id = 1;

SELECT * FROM r;

+----------------------------+----------------------------+------+
| d                          | ts                         | id   |
+----------------------------+----------------------------+------+
| 2017-07-01 00:00:00.000000 | NULL                       |    2 |
+----------------------------+----------------------------+------+

The explicit_defaults_for_timestamp Variable

The variable explicit_defaults_for_timestamp determines if certain nonstandard behaviors for default values and NULL-value are disabled for the TIMESTAMP column. By default, the variable is enabled, which disables the nonstandard behaviors.

If the explicit_defaults_for_timestamp variable is enabled, SingleStore Helios handles the TIMESTAMP column behavior as follows:

• Assigning a TIMESTAMP column value of NULL does not set it to the current timestamp. To set to the current timestamp, set the TIMESTAMP column to CURRENT_TIMESTAMP() or NOW().

• If the TIMESTAMP column is not declared as NOT NULL, then it is automatically declared with the NULL attribute and permits NULL values. Assigning a value of NULL to the column sets it to NULL, not the current timestamp.

• TIMESTAMP column declared with the NOT NULL attribute do not permit NULL values.

• TIMESTAMP columns explicitly declared with the NOT NULL attribute and without an explicit DEFAULT attribute are treated as having no default value.

• To declare TIMESTAMP column with the DEFAULT CURRENT_TIMESTAMP() or ON UPDATE CURRENT_TIMESTAMP() attributes, these must be explicitly specified.

• The first TIMESTAMP column in a table is handled in the same way as the TIMESTAMP columns following the first one.

If the explicit_defaults_for_timestamp variable is disabled, SingleStore Helios handles the TIMESTAMP column behavior as follows:

• If the TIMESTAMP column is not declared as NULL, then it is automatically declared with the NOT NULL attribute. Assigning a value of NULL to the column is permitted and sets the column to the current timestamp.

• The first TIMESTAMP column in a table, if not declared as NULL, DEFAULT CURRENT_TIMESTAMP() or ON UPDATE CURRENT_TIMESTAMP(), is automatically declared with the DEFAULT CURRENT_TIMESTAMP() and ON UPDATE CURRENT_TIMESTAMP() attributes.

• TIMESTAMP columns following the first one, if not declared with the NULL attribute or a DEFAULT attribute, are automatically declared as DEFAULT0000-00-00 00:00:00 (the zero timestamp).

Handling of Time Zones

SingleStore Helios currently ignores any time zone offsets on query writes and reads for DATETIME and TIMESTAMP data types. The time zone defaults to UTC.

See the following examples for DATETIME and TIMESTAMP respectively:

CREATE TABLE dt (id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,  
                 col DATETIME NOT NULL
                 );

INSERT INTO dt (col) VALUES ('2022-01-01 10:10:10'), 
                            ('2022-01-01 10:10:10+05:30'), 
                            ('2022-01-01 10:10:10-08:00');

SELECT * FROM dt;

+----+---------------------+
| id | col                 |
+----+---------------------+
|  1 | 2022-01-01 10:10:10 |
|  2 | 2022-01-01 10:10:10 |
|  3 | 2022-01-01 10:10:10 |
+----+---------------------+

CREATE TABLE ts (id INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY,        
                 col TIMESTAMP NOT NULL
                 );

INSERT INTO ts (col) VALUES ('2022-01-01 10:10:10'),        
                            ('2022-01-01 10:10:10+05:30'), 
                            ('2022-01-01 10:10:10-08:00');

SELECT * FROM ts;

+----+---------------------+
| id | col                 |
+----+---------------------+
|  1 | 2022-01-01 10:10:10 |
|  2 | 2022-01-01 10:10:10 |
|  3 | 2022-01-01 10:10:10 |
+----+---------------------+

If the data_conversion_compatibility_level is 7.0 or higher and if any extra characters are included in the query (including a timezone), an error will be generated.

SELECT @@data_conversion_compatibility_level;

+---------------------------------------+
| @@data_conversion_compatibility_level |
+---------------------------------------+
| 7.5                                   |
+---------------------------------------+

CREATE TABLE dt1 (id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, col DATETIME NOT NULL);
INSERT INTO dt1 (col) VALUES ('2022-01-01 10:10:10'),     
                            ('2022-01-01 10:10:10+05:30'),    
                            ('2022-01-01 10:10:10-08:00');

ERROR 2363 (HY000): Leaf Error (127.0.0.1:3307): Invalid DATE/TIME in type conversion

Zero Value Time and Date

The ability to enter a zero value into a time or date column (for example, 0000 for a YEAR column) is controlled by the data_conversion_compatibility_level.

CREATE TABLE ztest(id int, zy year);

INSERT INTO ztest VALUES(2, 0000);

ERROR 1264 (22003): Leaf Error (127.0.0.1:3306): Out of range value for column 'zy'

SELECT @@data_conversion_compatibility_level;

+---------------------------------------+
| @@data_conversion_compatibility_level |
+---------------------------------------+
| 8.0                                   |
+---------------------------------------+

Entering a zero value for year is restricted via data_conversion_compatibility_level. Set the value to a lower version in order to insert zero values:

SET GLOBAL data_conversion_compatibility_level = '6.0';

INSERT INTO ztest VALUES(2, 0000);

SELECT * FROM ztest;

+------+------+
| id   | zy   |
+------+------+
|    2 | 0000 |
+------+------+
1 row in set (0.321 sec)