Overview of Oracle Database Object Types and column data types

Major Data Types of database Classification

All object hava a name and atype, and each object is owned by a schema.

-- Query the main object types of a Database

Selectobject_type, count (object_type) from dba_objects

Group by object_typeorder by object_type;

Naming rules for database objects

1. The object name can contain a maximum of 30 characters, except databaselink. It can contain a maximum of 128 characters;

2. reserved keywords cannot be used for object names;

3. The object name must start with a letter

4. The object name can only contain three types of symbols: _ $ #

5. lowercase letters are automatically converted to uppercase letters.

6. If double quotation marks are used, the above rules can be broken.

Object namespace

The following objects use the same namespace:

TABLE	VIEWS	SEQUENCES
PRIVATE SYNONYMS	STAND-ALONE PROCEDURES	STAND-ALONE FUNCTIONS
PACKAGES	MATERIALIZED VIEWS	USER-DEFINED TYPES

The following objects have their own namespace

INDEX	CONSTRAINTS	CLUSTERS
DATABASE TRIGGERS	PRIVATE DATABASE LINKS	DIMENSIONS

Lists the data types available for data columns.

Character Type

VARCHAR2	Variable-length character type, 1byte-4KB, and VARCHAR type, which is automatically converted to VARCHAR2
NVARCHAR2	Similar to VARCHAR2, but can store international codes;
CHAR	The fixed length is 1 byte-2kb. If the character length is insufficient, use spaces to fill it up;

Value Type

NUMBER	Precision (1 to 38) sacle (-84,127) NUMBER (precision, scale) Precision indicates the valid digit in the number. If precision is not specified, Oracle uses 38 as the precision. Scale indicates the number of digits to the right of the decimal point. scale is set to 0 by default. If scale is set to a negative number, Oracle will select this number to the specified number to the left of the decimal point.
FLOAT	Precision (138) BINARY_FLOAT BINARY_DOUBLE
INTEGER	Equivalent to NUMBER, with scale zero

Time Type

DATE	Century, year, month, day, hour, minute, second range from January 1, 4712 BC, to December 31, 9999 after the ad, can be blank or 7 bytes
TIMESTAMP	Similar to date, but the second accuracy is more accurate. It can be null or 11 bytes.
TIMESTAMP WITH TIMEZON
TIMESTAMP WITH LOCAL TIMEZONE
INTERVAL YEAR TO MONTH
INTERVAL DAY TO SECOND

Big Data Type

CLOB
NCLOB
BLOB
BFILE
LONG
LONG RAW

Other Types

RAW
ROWID