creating and managing tables

Creating and Managing Tables

Objectives

At the end of this lesson, you will be able to:

Describe the main database objectsCreate tablesDescribe the datatypes that can be used when specifying column definitionAlter table definitionsDrop, rename and truncate tables

Naming Conventions

Can be 1–64 characters longMust contain only A–Z, a–z, 0–9, _ , and $Must not duplicate the name of another object owned by the same userMust not be a MySQL reserved wordMust begin with a letter or digit

Required

Naming Conventions

Field names should be descriptive.Use the underscore (_) to separate words.Use entirely lowercase words (this is a personal preference rather than a rule).Use plural table names (to indicate multiple values stored) and singular column names.End primary and foreign key columns with id (or ID)List the primary key first in a table, followed by foreign keys.

Suggested

The CREATE TABLE Statement

You must have :CREATE TABLE privilegeA storage area

You specify:Table nameColumn name, column datatype, and column size

CREATE TABLE [schema.]table (column datatype [DEFAULT expr]);

The DEFAULT Option

Specify a default value for a column during an insert.

Legal values are literal value, expression, or MySQL function.Illegal values are another column’s name or pseudocolumn.The default datatype must match the column datatype.

… hire_date DATE DEFAULT CURDATE(), …

Creating TablesCreating the table

Confirm table creation

MySQL> CREATE TABLE dept -> (dept_nbr INTEGER(2), -> dept_name VARCHAR(14), -> location VARCHAR(13));Table created.

MySQL> DESCRIBE dept

Name Null? Type --------------------------- -------- --------- dept_nbr INTEGER(2) dept_name VARCHAR(14) locaton VARCHAR(13)

Querying the Data Dictionary

Show tables owned by the user.

MySQL> SHOW TABLES;

DatatypesNumeric Types

Type Size Description

TINYINT [Length] 1 byte Range of -128 to 127 or 0 to 255 unsigned.

SMALLINT [Length] 2 bytes Range of -32, 768 to 32,767 or 0 to 65535 unsigned.

MEDIUMINT [Length] 3 bytes Range of -8, 388, 608 to 8, 388, 607 or 0 to 16, 777, 215 unsigned

INT [Length] 4 bytes Range of -2, 147, 483, 648 to 2, 147, 483, 647 or 0 to 4, 294, 967, 295 unsigned

BIGINT [Length] 8 bytes Range of -9, 223, 372, 036, 854, 775, 808 to 9, 223, 372, 036, 854, 774, 807 or 0 to 18, 446, 744, 073, 709, 551, 615 unsigned

FLOAT [Length, Decimals] 4 bytes A small number with a floating decimal point.

DOUBLE [Length, Decimals] 8 bytes A large number with a floating decimal point.

DECIMAL [Length, Decimals] Length + 1 or Length + 2 bytes

A DOUBLE with a fixed decimal point.

Bold item most frequently used in Business Environments

DatatypesText TypesType Size Description

CHAR [Length] Length bytes A fixed-length field from 0 to 255 characters long.

VARCHAR [Length] String length + 1 or 2 bytes

A fixed-length field from 0 to 255 characters long. (65,535 characters long as of MyMySQL 5.0.3)

TINYTEXT String length + 1 bytes A string with a maximum length of 255 characters.

TEXT String length _ 2 bytes A string with a maximum length of 65,535 characters.

MEDIUMTEXT String length + 3 bytes A string with a maximum length of 16,777,215 characters.

LONGTEXT String length + 4 bytes A string with a maximum length of 4,294,967,295 characters.

BINARY [Length] Length bytes Similar to CHAR but stores binary data.

VARBINARY [Length] Data length + 1 bytes Similar to VARCHAR but stores binary data.

TINYBLOB Data length + 1 bytes Stores binary data with a maximum length of 255 bytes.

BLOB Data length + 2 bytes Stores binary data with a maximum length of 65,535 bytes.

MEDIUM BLOB Data length + 3 bytes Stores binary data with a maximum length 16,777,215 bytes.

LONGBLOB Data length + 4 bytes Stores binary data with a maximum length of 4,294,967,295 bytes.

ENUM 1 or 2 bytes Short for enumeration, which means that each column can have one of several possible values.

SER 1, 2, 3, 4, or 8 bytes Like ENUM except that each column can have more than one of several possible values.

Bold item most frequently used in Business Environments

DatatypesDate and Time Types

Type Size Description

DATE 3 bytes In the format of YYYY-MM-DD.

DATETIME 8 bytes In the format of YYYY-MM-DD HH:MM:SS

TIMESTAMP 4 bytes In the format of YYYYMMDDHHMMSS; acceptable range ends in the year 2037.

TIME 3 bytes In the format of HH:MM:SS.

YEAR 1 byte In the format of YYYY, with a range from 1901 to 2155.

Bold item most frequently used in Business Environments

The ALTER TABLE Statement

Use the ALTER TABLE statement to:Add a new columnModify an existing columnDefine a default value for the new column

ALTER TABLE tableADD (column datatype [DEFAULT expr]

[, column datatype]...);

ALTER TABLE tableMODIFY (column datatype [DEFAULT expr]

[, column datatype]...);

Adding a Column

Department30employee_nbr name annual_salary hire_date

7698 Blake 34200 2001-05-01 7654 Martin 15000 2001-09-28 7499 Allen 19200 2001-02-20 7844 Turner 18000 2001-09-08...

“…add a newcolumn intoDepartment30 table…”

Department30

job

New column

employee_nbr name annual_salary hire_date

7698 Blake 34200 2001-05-01 7654 Martin 15000 2001-09-28 7499 Allen 19200 2001-02-20 7844 Turner 18000 2001-09-08...

job

Adding a ColumnYou use the ADD clause to add columns.

The new column becomes the last column.

MySQL>ALTER TABLE dept30 ->ADD (job VARCHAR(9));Table altered.

employee_nbr name annual_salary hire_date job------------ ----- ------------- --------- --- 7698 Blake 34200 2001-05-01 7654 Martin 15000 2001-09-28 7499 Allen 19200 2001-02-20 7844 Turner 18000 2001-09-08...6 rows selected.

Modifying a ColumnYou can change a column’s datatype, size, and default value.

A change to the default value affects only subsequent insertions to the table.

ALTER TABLE dept30MODIFY (name VARCHAR(15));Table altered.

Dropping a Table

All data in the table is deleted.Any pending transactions are committed.All indexes are dropped.You cannot roll back this statement.

MySQL> DROP TABLE dept30;Table dropped.

Dropping a Column

All data in the column is deleted.Any pending transactions are committed.You cannot roll back this statement.

MySQL> ALTER TABLE tablename DROP COLUMN (columname) [CASCADE CONSTRAINTS]

Changing the Name of an Object

To change the name of a table, view, sequence, or synonym, you execute the RENAME statement.

You must be the owner of the object.

MySQL> RENAME dept TO department;Table renamed.