====== LU06b - SQL-DDL: Table Management ======

**Source**: 
  * [[https://www.w3schools.com/sql/sql_create_table.asp| W3Schools |CREATE TABLE]]
  * [[https://www.w3schools.com/sql/sql_alter.asp| W3Schools | ALTER TABLE]]
  * [[https://www.w3schools.com/sql/sql_drop_table.asp| W3Schools | DROP TABLE]]
 
===== Learning Objectives =====
In this learning unit, we will learn how to manage database tables, i.e. 
  -how to create
  -how to modify and 
  -how to delete database tables

===== CREATE TABLE =====
Let's start by creating a table based on the ERD of the student management tool, as shown below:

Our goal is to create the table "stundent" in our database. For that we need to know how the basic syntax for creating of table is.

  CREATE TABLE table_name (
      column1 datatype,
      column2 datatype,
      column3 datatype,
     ....
  );

In our example the our concrete CREATE statement would look like:
''
  CREATE TABLE student (
    stundent_id INT,
    name VARCHAR(50),
    surname VARCHAR(50),
    birthdate DATE,
    matrno CHAR(6)
  );
  
After executing the DDL create command, the result would look like the following illustration. 

{{:modul:m290:learningunits:lu05:theorie:m290_lu06b.abb2.png?600|}}

**Hints:** 
  * On the right upper side you can see, that the table "student" has actually been created. 
  * After a select on this table, we can see that the table does not yet contain any data.
  * It's not a big deal so far, is it? 8-).

===== ALTER TABLE =====
It may happen that we need to change something, e.g. the change the attribute name or add a new attribute. In this case, the ALTER TABLE commands will do the work.

The basic syntax of the DDL "ALTER TABLE" syntax is:

  ALTER TABLE table_name
  ADD column_name datatype;
  
==== ADD COLUMN ====
In practical use, if we want to add an email to the student's data our SQL command would look like:

  ALTER TABLE student
  ADD Email varchar(255);
  
==== DROP COLUMN ====
If we can add a column, it should come as no surprise that we also can delete a column. The syntax for deleting an entire column from a table is:

  ALTER TABLE table_name
  DROP COLUMN column_name;
  
The following DDL statement removes the currently added column email from the table student.
  
  ALTER TABLE Customers
  DROP COLUMN Email;

==== RENAME COLUMN ====
Naturally, we also can just rename a wrongly spelled column name. The syntax in that case is:
  
  ALTER TABLE table_name
  RENAME COLUMN old_name to new_name;
 
Or more practical, if we want to change the name of the column  matrno in studentno, we need the following DDL command:

  ALTER TABLE student
  RENAME COLUMN matrno to studentno;
  
==== MODIFY DATATYPE ====
We also can change the datatype of colums. The basic syntax would be: 

  ALTER TABLE table_name
  ALTER COLUMN column_name datatype;
  
And of course, as a concrete practical example, in which we change the length of the column "name" from 50 characters to 100:
 
  ALTER TABLE student
  MODIFY COLUMN name VARCHAR(100);
  
===== DROP TABLE =====
If, for whatever reason, we have created a table incorrectly or want to get rid of an obsolete table, we need the command DROP TABLE:

  DROP TABLE table_name;

**Hint: <color #ed1c24>Be careful with this command, as it also deletes the entire contents of this table.</color>**

==== Vocabulary ====
^English ^ Deutsch ^
| column | Spalte |

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[[https://creativecommons.org/licenses/by-nc-sa/4.0/|{{https://i.creativecommons.org/l/by-nc-sa/4.0/88x31.png}}]] Volkan Demir