How to know relations between tables

Question

I have a database in MySQL created by someone. I don't have any documentation of the database.

How can I know the relationship between the tables?

Is there any query or a procedure to generate a report so that it's easy to find the relations?

I can look into Schema information and manually figure it out, but it would be great if I could generate a relationship report.

Answer 1

You can get an overview in MySql Workbench by doing the steps below:

1. Go to "Database" Menu option.
2. Select the "Reverse Engineer" option.
3. A wizard will be opened and will generate an EER Diagram which shows up

Answer 2

Try out SchemaSpy ( http://schemaspy.sourceforge.net/ ):

SchemaSpy is a Java-based tool (requires Java 5 or higher) that analyzes the metadata of a schema in a database and generates a visual representation of it in a browser-displayable format.

Here is a screenshot of the HTML page of the sample output from http://schemaspy.sourceforge.net/sample/ :

There is also a nice GUI if you do not want to use the command line: http://schemaspygui.sourceforge.net/

Both tools are open source and in my opinion very lightweight and easy to use. I used them several times when I was in situations that you described: To get an overview of the schema and even some details to dive deeper. (Take a look at the "Anomalies" report.)

---

Update

Be sure to check out the upcoming version of SchemaSpy at http://schemaspy.org

Answer 3

The better way as programmatically speaking is gathering data from INFORMATION_SCHEMA.KEY_COLUMN_USAGE table as follows:

SELECT 
  `TABLE_SCHEMA`,                          -- Foreign key schema
  `TABLE_NAME`,                            -- Foreign key table
  `COLUMN_NAME`,                           -- Foreign key column
  `REFERENCED_TABLE_SCHEMA`,               -- Origin key schema
  `REFERENCED_TABLE_NAME`,                 -- Origin key table
  `REFERENCED_COLUMN_NAME`                 -- Origin key column
FROM
  `INFORMATION_SCHEMA`.`KEY_COLUMN_USAGE`  -- Will fail if user don't have privilege
WHERE
  `TABLE_SCHEMA` = SCHEMA()                -- Detect current schema in USE 
  AND `REFERENCED_TABLE_NAME` IS NOT NULL; -- Only tables with foreign keys

and another one is

select * from INFORMATION_SCHEMA.TABLE_CONSTRAINTS;

Answer 4

Do you have the SELECTs that use the database? That may be the best source of the relationships.

Answer 5

一个更有价值的选择可能是你只需要安装mysql workbench。（ 参考 ）并尝试“从数据库创建EER模型”。你肯定能够看到表之间的关系。

Answer 6

You may take a look at information_scheme.KEY_COLUMN_USAGE table

As it is suggested there a quick way to list your FKs (Foreign Key references) using the KEY_COLUMN_USAGE view:

SELECT CONCAT( table_name, '.',
column_name, ' -> ',
referenced_table_name, '.',
referenced_column_name ) AS list_of_fks
FROM information_schema.KEY_COLUMN_USAGE
WHERE REFERENCED_TABLE_SCHEMA = (your schema name here)
AND REFERENCED_TABLE_NAME is not null
ORDER BY TABLE_NAME, COLUMN_NAME;

Answer 7

If you are using phpmyadmin then:

1. Goto the database.
2. Select the table and goto its structure.
3. You'll find relation view at the bottom of your table structure.

Answer 8

Better you use Mysql workbench. There is an option for generating ER diagram. If you are using phpmyadmin select any table. There is structure tab from where you can see the table structure. Hopefully, this will help.