SQL Optimizations, Activiti, basic data types, wrapper data types supplements

SQL optimization

1. Avoid using in and not in,or,having in the WHERE statement

exist, not exist instead of in, no in

2. Cannot declare a number in character format, to declare character values in numeric format, otherwise invalidates the index, resulting in full table scan

3. SQL statements are capitalized, because Oracle always converts lowercase to uppercase before executing

4, not using not in the index, using not will produce and use the same effect as the function, resulting in a full table scan

5, there are sub-query when using join instead of sub-query, no sub-query when less with join

6, less use select*

7. Use UNION ALL instead of union and OR

8. Avoid using in where! = and >, < operator, causes full table scan

Activiti

1, is a framework of workflow, in line with the BPMN standard.

2, Activiti features: Data persistence, Engine service interface, process designer, native support spring, separate runtime and historical data.

3. Activiti Engine: Generate the core parts of the report

Activiti Modeler: Model Designer

Activiti Design: Designer

Activiti exploer: Process Management

4, the use of the language is Javadocs, the environment configuration needs to use the JDK, ant, maven, can be done after the most simple leave process test

5, a process in the BPMN2.0 specification is divided into start events, end events. The startup events are divided into: null start, timed start, abnormal start. The end event is divided into: null end, end of exception, end of cancellation.

6, the task is an important part of the process, divided into: User tasks, Script tasks, webservice tasks, etc.

7, the gateway is used to control the flow trend, divided into: exclusive gateway, parallel Gateway, inclusive gateway, event gateway to see 113 sides

Basic data types: Byte, short, int, long

float, double, char, Boolean

Data type size Range                                     Default value
Byte (bytes) 8-128-127 0
Shot (short-integer) 16-32768-32768 0
int (integral type) 32-2147483648-2147483648 0
Long (length) 64-9233372036854477808-9233372036854477808 0
Float (float type) 32-3.40292347e+38-3.40292347e+38 0.0f
Double (dual precision) 64-1.79769313486231570e+308-1.79769313486231570e+308 0.0d
char (character type) + ' \U0000-U\FFFF ' ' \u0000 '
Boolean (Boolean) 1 True/false False

Basic data types	Packing class
Byte	Byte
Boolean	Boolean
Short	Short
Char	Character
Int	Integer
Long	Long
Float	Float
Double	Double

The difference is that the Char wrapper type is: Character int packing type: Integer

SQL Optimizations, Activiti, basic data types, wrapper data types supplements