SQL built-in functions

SQL Server has many built-in functions. Below I will summarize my frequently used functions:

1. getdate () obtains the current system time.

2. datediff (unit of difference, previous time, and later time) Comparison Time Difference

Example: Select datediff (day, '2017-03-14 ', getdate ())

Result 1

Note: The result is a negative value (after time-before time!

3. Convert () data type conversion

Let's talk about common date conversion for specific string formats

Convert (varchar, time, style number)

For example, the time is 23:29:37. 703 (obtained using the preceding getdate)

Style number: 8 in the format of 23:30:37

23 format:

20 format: 23:31:09

Note: you do not need to specify the length of varchar.

4. sum (), max (), min (), AVG (), count ()

Note: These functions ignore null values.