information_schema.tables – Database Research & Development

MySQL: Script to find Missing Indexes for particular type of Columns

Anvesh Patel — Tue, 04 Jul 2017 16:16:51 +0000

In this post, I am sharing a script to find missing indexes in MySQL only for those columns which name ended with ‘_id’.

The full table scanning is always creating a performance issue for any database.

As a Database Professional, you might be adding database indexes on a table but periodically the volume of data is changing so we need to analyze the old indexes, or we should find missing indexes which may require for query optimizer.

On the other hand, Database Administrator may also require a report on missing indexes which they can share with developers and users so that they can modify it.
SELECT 
	t.TABLE_SCHEMA
	,t.TABLE_NAME
	,c.COLUMN_NAME
	,IFNULL(kcu.CONSTRAINT_NAME, 'Not indexed') AS Indexed
FROM information_schema.TABLES as t
INNER JOIN information_schema.COLUMNS as c
	ON c.TABLE_SCHEMA = t.TABLE_SCHEMA
		AND c.TABLE_NAME = t.TABLE_NAME
		AND c.COLUMN_NAME LIKE '%_id'
LEFT JOIN information_schema.KEY_COLUMN_USAGE as kcu
	ON kcu.TABLE_SCHEMA = t.TABLE_SCHEMA
		AND kcu.TABLE_NAME = t.TABLE_NAME
		AND kcu.COLUMN_NAME = c.COLUMN_NAME
		AND kcu.ORDINAL_POSITION = 1
WHERE kcu.TABLE_SCHEMA IS NULL
AND t.TABLE_SCHEMA NOT IN ('information_schema', 'performance_schema', 'mysql');

MySQL: Script to find Largest Databases size on Server

Anvesh Patel — Mon, 17 Oct 2016 17:16:57 +0000

In this post, I am sharing a useful DBA script to find largest databases on MySQL Server.

This kind of handy script always useful while DBA requires quick monitoring on the Database Server.
So, I am always finding this kind of script and sharing here for making DBA task easier.

I prepared few calculated columns with the help of information_schema.TABLES.

SELECT
	COUNT(*) AS TotalTableCount
	,table_schema
	,CONCAT(ROUND(SUM(table_rows)/1000000,2),'M') AS TotalRowCount
	,CONCAT(ROUND(SUM(data_length)/(1024*1024*1024),2),'G') AS TotalTableSize
	,CONCAT(ROUND(SUM(index_length)/(1024*1024*1024),2),'G') AS TotalTableIndex
	,CONCAT(ROUND(SUM(data_length+index_length)/(1024*1024*1024),2),'G') TotalSize	
FROM information_schema.TABLES
GROUP BY table_schema
ORDER BY SUM(data_length+index_length) 
DESC LIMIT 10;

MySQL: How to TRUNCATE all Tables of a Database?

Anvesh Patel — Thu, 29 Sep 2016 16:16:57 +0000

In this post, I am sharing one script to generate TRUNCATE TABLE script for all tables of MySQL Database Server.

Generally, Database Developer creates a testing tables in development or report database server and even sometimes it is required to TRUNCATE all tables of a database.

I have prepared one small script using INFORMATION_SCHEMA.TABLES which generates TRUNCATE TABLE script for all tables and you can also apply filters like: database_name, table_name.

SELECT CONCAT('TRUNCATE TABLE ',table_schema,'.',TABLE_NAME, ';') 
FROM INFORMATION_SCHEMA.TABLES
WHERE table_schema IN ('database_name')

You can copy the result of this script and can perform TRUNCATE operation for multiple tables.

During TRUNCATE operation if you get any error like foreign key constraint fail, then you can enable and disable FOREIGN_KEY_CHECKS.

Error like:

ERROR 1217 (23000): Cannot delete or update a parent row: a foreign key constraint fails

Disable Foreign Key:

SET FOREIGN_KEY_CHECKS=0;

Enable Foreign Key:

SET FOREIGN_KEY_CHECKS=1;

MySQL: Script to find last Updated time of the Table

Anvesh Patel — Fri, 26 Feb 2016 19:29:45 +0000

In this post, I am sharing a DBA query to find the last updated time of the MySQL Table.

We can also check the row level last updated time by adding one extra column into a table like last_updated_datetime.
For reporting purposes, we are using this approach to check the row level last updated DateTime.

As a Database Administrator, we are also responsible for monitoring some of the important tables of our MySQL database.

We can use information_schema.tables to find the information of the MySQL tables.

Using information_schema.tables:

SELECT UPDATE_TIME
FROM information_schema.tables
WHERE TABLE_SCHEMA = 'Database_Name'
   AND TABLE_NAME = 'Table_Name';

Using Status Command:

SHOW TABLE STATUS FROM Database_Name LIKE 'Table_Name';