Mysql note 4_function

Common functions:

Concat connection function Lower to lowercase upper to uppercase Length substr substring now current time Year current Year...

Process functions:

If the ifnull (column, result1, result2) field is null, result2 is returned. If the field is not empty, result1 is returned.

Case... when... then... else... end Branch statement.

Aggregate functions:

AVG average sum max min count [distinct] count, null value no count.

Comparison between where and having:

Are used as conditions, but having can only be used.

Where having

After Group

You cannot use composite functions.

Order by is used after both

Limits on Limit results:

Limit 5; search for the first five

Limit5, 10; Retrieve 6-15

Structure:

Select...

From...

Where...

Group...

Having...

Limit...

Order...