Referential Integrity Referential integrity means that relationships between tables are consistent. MySQL enforces referential integrity by using foreign key constraints. When one table (the child table) has a foreign key to another table (the parent table), MySQL prevents you from adding a record to the child table if there is no corresponding record in the parent table. It also facilitates cascading updates and deletes to ensure that changes made to the child table are reflected in the parent … [Read more...] about How to use foreign keys to attain referential integrity in MySQL
Beginners Guide to Storage Engines in MySQL
Storage Engines and MySQL When you create a table, MySQL uses the InnoDB storage engine to create the storage for that table on the hard disk. You can choose an alternative storage engine to use for each table. Typically, you make this choice according to which storage engine offers features that best fit the needs of your application. Each storage engine has a particular set of operational characteristics. These characteristics include the types of locks that are used to manage query … [Read more...] about Beginners Guide to Storage Engines in MySQL
How to obtain MySQL metadata (metadata access methods)
A database is a structured collection of data. Metadata is "data about data". Using the following methods, MySQL provides access to metadata for databases, tables, and other objects managed by the database server: 1. INFORMATION_SCHEMA: The MySQL server contains a data dictionary implemented as a database (schema) named INFORMATION_SCHEMAthat includes a number of objects that appear to be tables. 2. SHOW statements: Proprietary syntax to obtain data on server statistics, schemas, and … [Read more...] about How to obtain MySQL metadata (metadata access methods)
“Access denied for user ‘username’@’hostname’ (using password: YES)” – Error while connecting MySQL with PHP
The Problem If the MySQL password contains a dollar sign character '$', PHP is unable to connect and issues an error like: Access denied for user 'username'@'hostname' (using password: YES) Connections via other clients work correctly. The Solution PHP interprets dollar signs inside of double quotes as starting a variable name, which will be expanded. This expansion will change the password sent to MySQL. There are 3 ways to avoid this problem: Escape the character with a … [Read more...] about “Access denied for user ‘username’@’hostname’ (using password: YES)” – Error while connecting MySQL with PHP
How to Restrict MySQL User Creation with Blank Password
Question: How can we not allow user creation with a blank password in MySQL? Using a blank password for a user is always a no go. In order to restrict user creation with blank password follow the steps given below: Before MySQL 5.6 In case of MySQL version below 5.6, this can not be achieved completely. But there are settings that can be used to come closer to our objective. Set the below SQL mode on the MySQL instance: SET SQL_MODE = NO_AUTO_CREATE_USER Using NO_AUTO_CREATE_USER … [Read more...] about How to Restrict MySQL User Creation with Blank Password
Beginners Guide to MySQL Data Types
Data Types: Overview In MySQL, the available data types can be grouped into four major categories: Numeric: Numeric values Binary: Binary data strings Character: Text strings Temporal: Time and date values Within each category, there are numerous specific data types that use varying amounts of memory and disk space, and thus have varying effects on performance. Choosing the best data type for the column has a rather small effect on performance in an individual record, but as the … [Read more...] about Beginners Guide to MySQL Data Types