Detailed graphic explanation of mysql query control statements

mysql query control statements

Field deduplication

**Keyword: distinct**
Syntax: select distinct field name from table name;

Case: Deduplication of departments

Select distinct dep from emp; 

ifnull syntax

Null plus any number equals null

Use ifnull to replace null values

Syntax: Select ifnull (field name that may be empty, if empty, replace it with something) from table name;

Example: View the sum of an employee's monthly salary and commission

Select sal+ifnull(comm,0) from emp;

Aliasing fields

Method: select field name as alias from table name

Select field name alias from table name

Sorting:

		Keywords: order by
		Syntax: Select field name from table name order by field name (used for sorting) asc (ascending)/desc (descending)

Aggregate functions:

MySQL provides aggregate functions for calculating fields.
Sum(): sums a whole column of data
Count(): count the number of nulls and do not count
Max(): Maximum value
Min(): minimum value
Avg(): average value
Round(): round the decimal places (..., how many places)

Example: Total salary

Summarize

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