1. Structured Query Language (Data definition Language)
SQL - DDL
Structured Query Language (Data definition Language)

2. Data Definition Language (SQL)
A data definition language or data description language (DDL) is a syntax similar to a computer programming language for defining data structures, especially database schemasD
SQL (Structured Query Language) – has a confusing name because of the word Query.
SQL – DML (Data Manipulation Language) allows the user/administrator to add, delete, modify and query data that is already in database tables.
SQL – DDL (Data Definition Language) allows the user/administrator to create, delete and change the structure of the tables and there inter-connection.
DDL doesn’t evolve querying and DML does a lot more that just querying. However SQL is the combination of DML and DDL.

3. ER – diagram

4. Creating A Table CREATE TABLE members ( Comments
userID varchar(40) NOT NULL,
password varchar(20) NOT NULL,
first varchar(20) NOT NULL,
last varchar(30) NOT NULL,
roles int,
UNIQUE (userID),
PRIMARY KEY (userID)
)ENGINE=InnoDB;
Comments
Making a field a primary key makes it UNIQUE and NOT NULL automatically so the NOT NULL and UNIQUE is overkill.

5. Foreign Key (total participation)
CREATE TABLE membersChallangeQuestions (
memberID varchar(40) ,
question varchar(100) NOT NULL,
answer varchar(50) NOT NULL,
FOREIGN KEY (memberID) REFERENCES members(userID),
PRIMARY KEY (memberID)
)ENGINE=InnoDB;
Comments
FOREIGN KEY requires that the memberID can only contain values that are in the userID column of the MEMBERS table.
To delete a member with a challenge question would now require the question get deleted first.
This table must be created after the members table.

6. Alter an existing Table’s definition
ALTER TABLE members ADD middle varchar(20); // add a middle name with 20 characters
ALTER TABLE members ADD middle varchar(20) AFTER first;
ALTER TABLE members ADD middle varchar(20) BEFORE last;
ALTER TABLE members ALTER middle varchar(30); // change middle name to 30 characters
ALTER TABLE members DROP middle; // get rid of middle name

7. Rename and create Like Table
CREATE TABLE newMembers LIKE members // create an empty table with same attributes
CREATE TABLE allMembers LIKE members // create a table with same attributes AS
( SELECT * FROM members ORDER BY last) // and populate with ordered data records
RENAME TABLE members TO oldMembers // archive members into old members

8. Change the name of a column with FK’s
ALTER TABLE members RENAME COLUMN userID to memberID
// This will fail because membersChallangeQuestion required the userID field
// We (the data base administrator DBA) need to do this in a few steps
ALTER TABLE `memberschallangequestions` DROP FOREIGN KEY IF EXISTS `object_ibfk_1`
ALTER TABLE membersChallangeQuestions ADD FOREIGN KEY (memberid) REFERENCES members(memberID)

9. M-N (many to many relation)
CREATE TABLE membersPhones (
memberID varchar(40) NOT NULL,
phoneID varchar(20) NOT NULL,
FOREIGN KEY (memberID) REFERENCES members(userID),
FOREIGN KEY (phoneID) REFERENCES phones(phoneID),
PRIMARY KEY (memberID, phoneID),
)ENGINE=InnoDB;
Comments
A new table to allow for the diamond with M-N relationship connecting members  phones
Since the combination of memberID and phoneID is a Primary Key, duplicates pairs and NULLs will not be allowed.

10. Truncate a table
TRUNCATE TABLE oldMembers // SQL-DDL will delete all rows in the oldMembers table
DELETE FROM oldMembers // SQL-DML will delete all rows in the oldMembers table
TRUNCATE is much faster than DELETE which will delete each row one at a time, checking for constraints, recalculating indexes each time etc.