MySQL Crash Course #13# Chapter 21. Creating and Manipulating Tables

Before manipulating the data in the table, now it is manipulating the table itself.

INDEX

• Create a multi-column primary key
• Provisions for automatic growth
• View the last inserted auto-increment id 
• Try to replace NULL with the default value
• Foreign keys cannot cross engines

• Add and delete fields & define foreign keys

• Modification of complex table structure

• Delete table and modify table name

Very neat. . Exemplary script:

CREATE TABLE customers
(
  cust_id      int       NOT NULL AUTO_INCREMENT,
  cust_name    char(50)  NOT NULL ,
  cust_address char(50)  NULL ,
  cust_city    char(50)  NULL ,
  cust_state   char(5)   NULL ,
  cust_zip     char(10)  NULL ,
  cust_country char(50)  NULL ,
  cust_contact char(50)  NULL ,
  cust_email   char(255) NULL ,
  PRIMARY KEY (cust_id)
) ENGINE=InnoDB;

To create a primary key made up of multiple columns

Simply specify the column names as a comma delimited list, as seen in this example:

CREATE TABLE orderitems
(
  order_num  int          NOT NULL ,
  order_item int          NOT NULL ,
  prod_id    char(10)     NOT NULL ,
  quantity   int          NOT NULL ,
  item_price decimal(8,2) NOT NULL ,
  PRIMARY KEY (order_num, order_item)
) ENGINE=InnoDB;

Provisions for automatic growth

CREATE TABLE `manga` (
  `manga_id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '漫画id',
  `manga_name` varchar ( 40 ) NOT  NULL COMMENT ' manga name ' ,
  `manga_discription` varchar ( 120 ) DEFAULT  NULL COMMENT ' manga description ' ,
  `manga_status` tinyint ( 4 ) NOT  NULL  DEFAULT  ' 0 ' COMMENT ' Comment description ' ,
   PRIMARY  KEY (`manga_id`)
) ENGINE = InnoDB AUTO_INCREMENT = 1012  DEFAULT CHARSET = utf8 COMMENT = ' comic table '  

Only one auto-incrementing column is allowed per table, and it must be indexed (for example, set it as the primary key)

View the auto-increment id of the last insertion,

Must be self-incrementing! Custom inserts do not count!

mysql> INSERT INTO manga
    -> (manga_name) VALUES ('what');
Query OK, 1 row affected (0.00 sec)

mysql> SELECT last_insert_id();
+------------------+
| last_insert_id() |
+------------------+
|             1012 |
+------------------+
1 row in set (0.00 sec)

Using DEFAULT Instead of NULL Values

Many database developers use DEFAULT values instead of NULL columns, especially in columns that will be used in calculations or data groupings.

Foreign Keys Can't Span Engines 

There is one big downside to mixing engine types. Foreign keys (used to enforce referential integrity, as explained in Chapter 1, "Understanding SQL") cannot span engines. That is, a table using one engine cannot have a foreign key referring to a table that uses another engine.

 Add and delete fields & define foreign keys

ALTER TABLE vendors
ADD vend_phone CHAR(20);

ALTER TABLE Vendors
DROP COLUMN vend_phone;

Modifying a table is often used to define foreign keys:

ALTER TABLE orderitems
ADD CONSTRAINT fk_orderitems_orders
FOREIGN KEY (order_num) REFERENCES orders (order_num);
ALTER TABLE orderitems
ADD CONSTRAINT fk_orderitems_products FOREIGN KEY (prod_id)
REFERENCES products (prod_id);

ALTER TABLE orders
ADD CONSTRAINT fk_orders_customers FOREIGN KEY (cust_id)
REFERENCES customers (cust_id);

ALTER TABLE products
ADD CONSTRAINT fk_products_vendors
FOREIGN KEY (vend_id) REFERENCES vendors (vend_id);

Syntax: ALTER TABLE table_name ADD CONSTRAINT fk_id FOREIGN KEY (foreign key field name) REFERENCES table indicates (the corresponding primary key field name in the foreign table);

FK_ID is the name of the foreign key. For more information about foreign keys, please refer to  Foreign Key Constraints

 Modification of complex table structure

Complex table structure changes usually require a manual move process involving these steps:

1. Create a new table with the new column layout.
2. Use the INSERT SELECT statement (see Chapter 19, "Inserting Data," for details of this statement) to copy the data from the old table to the new table. Use conversion functions and calculated fields, if needed.
3. Verify that the new table contains the desired data.
4. Rename the old table (or delete it, if you are really brave).
5. Rename the new table with the name previously used by the old table.
6. Re-create any triggers, stored procedures, indexes, and foreign keys as needed.

 Delete table and modify table name

DROP TABLE customers2;

RENAME TABLE backup_customers TO customers,
             backup_vendors TO vendors,
             backup_products TO products;