Introduction to MySQL SYSDATE()
In MySQL, we can find a range of Date and Time functions from which we can choose one for accessing the up-to-date date/time value. Most of these date and time functions are found synonyms to each one. From those, MySQL SYSDATE() function is responsible to provide the current date/time value when executed.
However, MySQL SYSDATE() function and MySQL NOW() function results to give the present date/time seems to be similar but they are a bit different in their behaviors. MySQL SYSDATE() function returns the strict date and time when it is executed on the server but MySQL NOW() function allows to provide a persistent date and time that signifies the time value at which the query or procedure was initiated to be executed.
The basic simple syntax structure for SYSDATE() function in MySQL is as follows:
Though it is a function we need not define any parameters for the function. But still we can add an optional parameter as ‘fsp’ that is accepted by the function which examines whether the output should contain a fractional part of seconds accuracy that arrays from 0 to 6. As
But its format in result output will differ if used in varying contexts. Suppose,
- If the context is a string, the SYSDATE() function returns the existing date in the format – YYYY-MM-DD HH:MM:SS.
- If the context is numeric, the SYSDATE() function returns the existing date in the format – YYYYMMDDHHMMSS.
How MySQL SYSDATE() Function works?
SYSDATE() function is useful to generate the current date and time and but it has also some caveats to know before we use it as it provides the time value of the execution period.
In MySQL, the result of SYSDATE() and NOW() functions both depend upon the execution time at which the query statement started and executed. This slightly makes a big dissimilarity in both the DATE functions in MySQL.
The difference between these two functions can be demonstrated with the help of example shown below:
Suppose, we have SYSDATE() and NOW() query and the result as:
SELECT NOW(), SYSDATE();
From the output above, it seems that the result value is identical for both which represents the current date and time of its execution .i.e. no difference.
But, again, if we provide a gap in between the query execution then the result might be hampered. For this, let us use the SLEEP() function which will pause the query statement execution time in seconds as specified in the argument.
SELECT NOW(), SLEEP(6), NOW();
Here, in the above example the NOW() while running was paused for some time i.e. 6s, but as the NOW() shows the steady time at which the command was started so the time does not affect.
Now, let us follow the same for SYSDATE() function and watch the difference using the query as follows:
SELECT SYSDATE(), SLEEP(6), SYSDATE();
As it is clear from the output displayed above as the result of SYSDATE() function that after the system sleep or pause of 6s in the execution period, the SYSDATE() function takes the time of current execution. In the same statement, the SYSDATE() shows values that vary in time interval where the last one adds 6s to its result set timestamp as it needs to show only the current time at which the query is finished processing the statement on the server.
But do remember that the SYSDATE function is considered as a non-deterministic. Therefore indexes cannot be operated for calculating terms that refer to it. Because during execution in the table columns having DATETIME data type, the SYSDATE() function might affect several rows or all rows data to evaluate the result as it does not make use of indexes but suppose if NOW() is used then, when we lookup through EXPLAIN clause statement, we can view a small number of rows are affected to search or calculate the result and provide the current date and time outputs.
So, it should be noticed to use the SYSDATE() function twice before considering it to be used in the database as it can have some negative reasons for it.
Also, the SET TIMESTAMP query in MYSQL does not affect the output value of the SYSDATE() function but may affect the output of the NOW() function.
This difference may cause some problems while performing the queries but we have a better option to avoid this. We can make SYSDATE() as an alias for MySQL NOW() function so that it shows similar behavior as NOW().
So, for this to be done, MySQL allows the use of –sysdate-is-now MySQL server command option. Using this, the dissimilarity may be removed and get the accurate result with date and time whenever the query statement is executed.
This alternative way can help to work on both the slave and master. This MySQL SYSDATE() function also might be unsafe for replication when the statement-based MySQL binary logging is implemented so, in this situation we can apply row-based MySQL logging on the server.
Examples to implement SYSDATE() function in MySQL
Let us take the following examples for understanding better:
Example #1 – Simple Example using SYSDATE()
We use SYSDATE() function in combination to SELECT SQL statement to run the command in MySQL as follows:
Example #2 – Fractional Seconds Precision
We are considering the SYSDATE() with fsp parameter value to return the result.
Example #3 – Numeric Context
This query will execute the result in the format specified as – YYYYMMDDHHMMSS.
SELECT SYSDATE() + 0;
Here, in the function you can even apply a nonzero value to either add or minus from the returning datetime value. View the below query with output:
SELECT SYSDATE() + 2;
- SYSDATE() function provides the current datetime of query execution while NOW() function returns the datetime at which the MySQL function triggering statement started.
- Thus, we can say the SYSDATE() function shows a self-executed interval of the function itself but not the query completing time on the server.
- Due to this, the timestamp returns the different values of execution when SYSDATE() and NOW() are implemented together.
This is a guide to MySQL SYSDATE(). Here we discuss how MySQL SYSDATE() Function works with query example to understand in easiest way. You may also have a look at the following articles to learn more –