2. [Mandatory] Names of tables and columns must consist of lower case letters, digits or underscores. Names starting with digits and names which contain only digits (no other characters) in between two underscores are not allowed. Columns should be named cautiously, as it is costly to change column names and cannot be released in pre-release environment.

Positive example: getter_admin, task_config, level3_name

Counter example: GetterAdmin, taskConfig, level_3_name

3. [Mandatory] Plural nouns are not allowed as table names.

4. [Mandatory] Keyword, such as desc, range, match, delayed, etc., should not be used. It can be referenced from MySQL official document.

5. [Mandatory] The name of primary key index should be prefixed with pk_, followed by column name; Unique index should be named by prefixing its column name with uk_; And normal index should be formatted as idx_[column_name].

6. [Mandatory] Decimals should be typed as decimal. float and double are not allowed.

7. [Mandatory] Use char if lengths of information to be stored in that column are almost the same.

8. [Mandatory] The length of varchar should not exceed 5000, otherwise it should be defined as . It is better to store them in a separate table in order to avoid its effect on indexing efficiency of other columns.

9. [Mandatory] A table must include three columns as following: id, gmt_create and gmt_modified.

Note: id is the primary key, which is unsigned bigint and self-incrementing with step length of 1. The type of gmt_create and gmt_modified should be DATE_TIME.

10. [Recommended] It is recommended to define table name as [tablebusiness_name][table_purpose].

11. [Recommended] Try to define database name same with the application name.

12. [Recommended] Update column comments once column meaning is changed or new possible status values are added.

13. [Recommended] Some appropriate columns may be stored in multiple tables redundantly to improve search performance, but consistency must be concerned. Redundant columns should not be:
  1) Columns with frequent modification.
  2) Columns typed with very long varchar or text.

14. [Recommended] Database sharding may only be recommended when there are more than 5 million rows in a single table or table capacity exceeds 2GB.

Note: Please do not shard during table creation if anticipated data quantity is not to reach this grade.

15. [For Reference] Appropriate char column length not only saves database and index storing space, but also improves query efficiency.