Removed images and added text tables (#35900)
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Uma Sankar
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Randell Dawson
Randell Dawson
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1f6b3c082d
@@ -12,57 +12,114 @@ We will cover:
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* Date Math
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* Dates in a where or having clause
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### Getting the current date
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### Let's Get Started :
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* ### Getting the current date :
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Getting the date from the system can be very handy for processing data using SQL.
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Getting the date from the system can be very handy for processing data using SQL.
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```sql
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-- current date
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select now(), sysdate(), current_date(), current_time(), -- date and time from the system on execution
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dayofyear(now()) as NumDaysSoFarThisYr,
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EXTRACT(YEAR FROM now()) as theYearPart,
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EXTRACT(YEAR_MONTH FROM now()) as theYrMonPart,
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date_format(now(), '%W %M %Y') as oneOfManyFormats;
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;
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```
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```sql
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-- current date
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select now(), sysdate(), current_date(), current_time(), -- date and time from the system on execution
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dayofyear(now()) as NumDaysSoFarThisYr,
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EXTRACT(YEAR FROM now()) as theYearPart,
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EXTRACT(YEAR_MONTH FROM now()) as theYrMonPart,
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date_format(now(), '%W %M %Y') as oneOfManyFormats;
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;
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```
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Result :
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```text
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+--------------------+----------------------+
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| now() | 2019-04-27 18:06:48 |
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| sysdate() | 2019-04-27 18:06:48 |
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| current_date() | 2019-04-27 |
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| current_time() | 18:06:48 |
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| NumDaysSoFarThisYr | 117 |
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| theYearPart | 2019 |
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| theYrMonPart | 201904 |
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| oneOfManyFormats | Saturday April 2019 |
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+--------------------+----------------------+
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```
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In SQL query, we see the following:
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* The first two columns in the result are two ways to get the same information: the date on the system at the time the SQL is executed.
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* The next two columns slice out just the Date and Time parts of the system date.
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* The next one presents the "day number" of the system date in this year. You'll notice that this is one day more than the math shown in the next example.
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* The next two extract just the year and then both the year and month
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* Last, but not least, there is a single example of one of the many ways to format this dates.
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In SQL query, we see the following:
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* The first two columns in the result are two ways to get the same information: the date on the system at the time the SQL is executed.
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* The next two columns slice out just the Date and Time parts of the system date.
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* The next one presents the "day number" of the system date in this year. You'll notice that this is one day more than the math shown in the next example.
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* The next two extract just the year and then both the year and month
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* Last, but not least, there is a single example of one of the many ways to format this dates.
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* ### Date Math :
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### Date Math
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```sql
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select now(), current_date(),
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datediff(now(),'2017-01-01') as daysThisYear,
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subdate(current_date(), interval 150 day) as '150DaysAgo',
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adddate(now(), interval 7 day) as dateInA_Week -- date in a week
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;
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```
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```text
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+------------------+----------------------+
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| now() | 2019-04-27 18:19:59 |
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| current_date() | 2019-04-27 |
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| daysThisYear | 846 |
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| 150DaysAgo | 2018-11-28 |
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| dateInA_Week | 2019-05-04 18:19:59 |
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+------------------+----------------------+
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```
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```sql
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select now(), current_date(),
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datediff(now(),'2017-01-01') as daysThisYear,
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subdate(current_date(), interval 150 day) as '150DaysAgo',
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adddate(now(), interval 7 day) as dateInA_Week -- date in a week
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;
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```
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Here we see:
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* The first two columns are just the system date and time for reference.
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* The second column is the date difference (datediff) between the first of January 2017 and the system date.
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* The last two columns are examples of subtracting and adding dates.
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* ### In a where or having clause :
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Here we see:
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* The first two columns are just the system date and time for reference.
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* The second column is the date difference (datediff) between the first of January 2017 and the system date.
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* The last two columns are examples of subtracting and adding dates.
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Here are two examples of using date math in a where clause:
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### In a where or having clause
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```sql
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select * from student; - to show the current data being used for the example
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select * from student where recordCreated < '2017-08-14';
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select * from student where recordCreated < subdate(current_date(), interval 628 day);
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```
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Result :
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Here are two examples of using date math in a where clause:
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```sql
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select * from student; - to show the current data being used for the example
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select * from student where recordCreated < '2017-01-01';
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select * from student where recordCreated < subdate(current_date(), interval 225 day);
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```
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```text
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+------------+---------------------+-----------+---------------+
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| studentID | FullName | sat_score | recordCreated |
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+------------+---------------------+-----------+---------------+
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| 1 | Jon snow | 200 | 2017-08-03 |
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| 2 | Stan Lee | 900 | 2017-08-05 |
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| 3 | Vincent Uvalle | 400 | 2017-08-07 |
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| 4 | Merle Veres | 800 | 2017-08-07 |
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| 5 | Donte Emmons | 1000 | 2017-08-07 |
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| 6 | Demetrius Mccaster | 1200 | 2017-08-07 |
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| 7 | Tim Goudy | 1400 | 2017-08-07 |
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| 8 | Stephan Monfort | 1600 | 2017-08-07 |
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| 9 | Maximo Backstrom | 1800 | 2017-08-14 |
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| 10 | Dean Pickel | 800 | 2017-08-14 |
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+------------+---------------------+-----------+---------------+
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```
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```text
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+------------+---------------------+-----------+---------------+
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| studentID | FullName | sat_score | recordCreated |
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+------------+---------------------+-----------+---------------+
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| 1 | Jon snow | 200 | 2017-08-03 |
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| 2 | Stan Lee | 900 | 2017-08-05 |
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| 3 | Vincent Uvalle | 400 | 2017-08-07 |
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| 4 | Merle Veres | 800 | 2017-08-07 |
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| 5 | Donte Emmons | 1000 | 2017-08-07 |
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| 6 | Demetrius Mccaster | 1200 | 2017-08-07 |
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| 7 | Tim Goudy | 1400 | 2017-08-07 |
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| 8 | Stephan Monfort | 1600 | 2017-08-07 |
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+------------+---------------------+-----------+---------------+
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```
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```text
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+------------+---------------------+-----------+---------------+
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| studentID | FullName | sat_score | recordCreated |
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+------------+---------------------+-----------+---------------+
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| 1 | Jon snow | 200 | 2017-08-03 |
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| 2 | Stan Lee | 900 | 2017-08-05 |
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+------------+---------------------+-----------+---------------+
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```
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Regarding the HAVING part: Keep in mind, most of the WHERE clause logic will also work in the HAVING clause of a GROUP BY. The difference between the two is that the WHERE clause runs against the full data, and the HAVING runs against the data aggregated by the GROUP BY clause.
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