dml

Why doesn't a TRUNCATE on mygroup work? Even though I have ON DELETE CASCADE SET I get: ERROR 1701 (42000): Cannot truncate a table referenced in a foreign key constraint ( mytest . instance , CONSTRAINT instance_ibfk_1 FOREIGN KEY ( GroupID ) REFERENCES mytest . mygroup ( ID )) drop database mytest; create database mytest; use mytest; CREATE TABLE mygroup ( ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY ) ENGINE=InnoDB; CREATE TABLE instance ( ID INT NOT NULL AUTO_INCREMENT PRIMARY KEY, GroupID INT NOT NULL, DateTime DATETIME DEFAULT NULL, FOREIGN KEY (GroupID) REFERENCES mygroup(ID) ON DELETE

I have heard the terms DDL and DML in reference to databases, but I don't understand what they are. What are they and how do they relate to SQL? DDL is Data Definition Language : it is used to define data structures . For example, with SQL, it would be instructions such as create table , alter table , ... DML is Data Manipulation Language : it is used to manipulate data itself . For example, with SQL, it would be instructions such as insert , update , delete , ... More information see here: MySQL What is DDL, DML and DCL? , the original is as follows: DDL DDL is short name of Data Definition