How to know relations between tables

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.

7 Answers

Answers 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

Answers 2

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; 

Answers 3

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.)

Answers 4

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; 

Answers 5

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

Answers 6

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.

Answers 7

One more valuable option may be if you just install mysql workbench.( refers to) And try "Create EER models from database" .You will surely able to see relations among tables.

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