In a relationship or a join, fields that are set to the AutoNumber data type are compatible with fields that are set to the Number data type if the Field Size property of the latter is Long Integer. You cannot change the data type or the Field Size property of a field that is involved in a table relationship. You can temporarily delete the relationship to change the Field Size property.
However, if you change the data type, you won't be able to re-create the relationship without first also changing the data type of the related field. For more information on tables see the article, Introduction to tables. When you apply a data type to a field, it contains a set of properties that you can select. Click on data types below for more information. Large Number. OLE Object.
Purpose Used in a field that allows attaching files or images to a record. For example, if you have a job contacts database, you can use an attachment field to attach a photo of the contact, or attach documents such as a resume. For some file types, Access compresses each attachment as you add it. Attachment data types are available only in. You can attach many kinds of files to a record.
However, some file types that may pose security risks are blocked. As a rule, you can attach any file that was created in one of the Microsoft Office programs.
You can also attach log files. For a list of supported image file formats, see the table later in this section. The label text that is displayed for this field by default in forms, reports, and queries. If this property is empty, the name of the field is used. Any text string is allowed. Access supports the following graphic file formats without the need for additional software being installed on your computer. In addition, file names must follow the following guidelines:.
Names cannot contain the following characters: question marks? Purpose Use an AutoNumber field to provide a unique value that serves no other purpose than to make each record unique. The most common use for an AutoNumber field is as a primary key, especially when no suitable natural key a key that is based on a data field is available.
An AutoNumber field value requires 4 or 16 bytes, depending on the value of its Field Size property. Suppose that you have a table that stores contacts' information. You can use contact names as the primary key for that table, but how do you handle two contacts with exactly the same name? Names are unsuitable natural keys, because they are often not unique. If you use an AutoNumber field, each record is guaranteed to have a unique identifier.
Note: You should not use an AutoNumber field to keep a count of the records in a table. AutoNumber values are not reused, so deleted records can result in gaps in your count. Moreover, an accurate count of records can be easily obtained by using a Totals row in a datasheet.
Determines the amount of space that is allocated for each value. For AutoNumber fields, only two values are allowed:. This is the default value.
You should not change this value unless you are creating a replication ID field. Note: Replication is not supported in databases that use a new file format, such as.
This setting makes AutoNumber fields compatible with other Long Integer Number fields when they are used in relationships or joins. Each field value requires 4 bytes of storage. Do not use this value unless you are working in or implementing the design of a replicated database.
Determines whether AutoNumber field increments with each new value or uses random numbers. Select one of the following:. Increment Starts with the value 1 and incrementally increases by 1 for each new record.
Random Starts with a random value and assigns a random value to each new record. Values are of the Long Integer field size, and range from -2,,, to 2,,, If you are using an AutoNumber field as a primary key or as a Replication ID, you should not set this property. Otherwise, choose a number format that meets your specific needs. Yes No duplicates Creates a unique index on the field. Yes Duplicates OK Creates a non-unique index on the field.
No Removes any index on the field. Note: Do not change this property for a field that is used in a primary key. Without a unique index, it is possible to enter duplicate values, which can break any relationships in which the key is a part. Although you can create an index on a single field by setting the Indexed field property, some kinds of indexes cannot be created in this manner.
For example, you cannot create a multi-field index by setting this property. Purpose Use to store the results of a calculation. Note, Calculated data types were first introduced in Access Calculated data types are available only in.
The result of this calculation will be stored in the calculated column. If this column has been saved, then only saved columns can be used in this expression. Determines the way that the field appears when it is displayed or printed in datasheets or in forms or reports that are bound to the field.
You can use any valid number format. In most cases, you should set the Format value to match the result type. Data in a Currency field is not rounded off during calculations. A Currency field is accurate to 15 digits to the left of the decimal point and 4 digits to the right.
Each Currency field value requires 8 bytes of storage. In most cases, you should set the Format value to Currency. Displays editing characters to guide data entry. For a single Logical field, the left-most high-order bit is used. When Logical fields occur consecutively, they are stored internally 8 per byte, left to right.
For applications with a large number of two-valued fields, this can result in a large reduction of storage requirement [compared to X 1 data type or I data type].
Before creating a database, you need to think about its purpose. What is the database going to be used for? What searches might be performed on it? In this film table example, the structure of the table would be:.
If you were creating a database about people, what data type would you use to capture someone's age? An alternative would be to capture their age as a number, like 15 or However, you need to think about the integrity of the database. If you input someone's age, you will need to update each record every time someone is a year older.
This would be inefficient and time consuming. The floating-point data types conform to IEEE in the following areas:.
See SQRT. Arithmetic operators conform. See "Arithmetic Operators". Comparison operators conform, except for comparisons with NaN. See "Floating-Point Conditions". Numeric precedence determines, for operations that support numeric data types, the data type Oracle uses if the arguments to the operation have different data types. Therefore, in any operation on multiple numeric values:. If any implicit conversion is needed and fails, then the operation fails. Do not create tables with LONG columns.
LONG columns are supported only for backward compatibility. LONG columns store variable-length character strings containing up to 2 gigabytes -1, or 2 31 -1 bytes. You can use LONG columns to store long text strings. The length of LONG values may be limited by the memory available on your computer.
The use of LONG values is subject to these restrictions:. However, you cannot then call the program unit from SQL.
MOVE statements. Triggers can use the LONG data type in the following manner:. Datetime and Interval Data Types. Values of datetime data types are sometimes called datetimes. Values of interval data types are sometimes called intervals. For information on expressing datetime and interval values as literals, refer to "Datetime Literals" and "Interval Literals". Both datetimes and intervals are made up of fields. The values of these fields determine the value of the data type.
Table lists the datetime fields and their possible values for datetimes and intervals. If the time zones have not been set manually, then Oracle Database uses the operating system time zone by default. If the operating system time zone is not a valid Oracle time zone, then Oracle uses UTC as the default value.
Table Datetime Fields and Values. The 9 n portion is not applicable for DATE. For a complete listing of all time zone region names, refer to Oracle Database Globalization Support Guide.
The DATE data type stores date and time information. Although date and time information can be represented in both character and number data types, the DATE data type has special associated properties.
For each DATE value, Oracle stores the following information: year, month, day, hour, minute, and second. A Julian day number is the number of days since January 1, BC. Julian days allow continuous dating from a common reference. These default values are used in a query that requests date values where the date itself is not specified, as in the following example, which is issued in the month of May:.
Example This statement returns the Julian equivalent of January 1, It stores the year, month, and day of the DATE data type, plus hour, minute, and second values. This data type is useful for storing precise time values and for collecting and evaluating date information across geographic regions. When you create a column of this data type, the value can be a number in the range 0 to 9. This data type is useful for preserving local time zone information.
Oracle time zone data may not reflect the most recent data available at this site. When a user retrieves the data, Oracle returns it in the user's local session time zone. This data type is useful for date information that is always to be displayed in the time zone of the client system in a two-tier application.
This data type is useful for representing the difference between two datetime values when only the year and month values are significant. You have a great deal of flexibility when specifying interval values as literals. Refer to "Interval Literals" for detailed information on specifying interval values as literals. Also see "Datetime and Interval Examples" for an example using intervals. This data type is useful for representing the precise difference between two datetime values.
Refer to "Interval Literals" for detailed information on specify interval values as literals. Oracle calculates the results based on the following rules:.
Oracle internally converts timestamp values to date values and interprets NUMBER constants in arithmetic datetime and interval expressions as numbers of days. You cannot multiply or divide date or timestamp values. Each DATE value contains a time component, and the result of many date operations include a fraction. This fraction means a portion of one day. For example, 1. The fractional portion of the result represents that portion of a day month.
If one operand is a DATE value or a numeric value, neither of which contains time zone or fractional seconds components, then:. Oracle implicitly converts the other operand to DATE data.
The exception is multiplication of a numeric value times an interval, which returns an interval. If the other operand has a time zone value, then Oracle uses the session time zone in the returned value. When interval calculations return a datetime value, the result must be an actual datetime value or the database returns an error.
For example, the next two statements return errors:. The first fails because adding one month to a day month would result in September 31, which is not a valid date. The second fails because adding one year to a date that exists only every four years is not valid. However, the next statement succeeds, because adding four years to a February 29 date is valid:.
Oracle performs all timestamp arithmetic in UTC time. Table is a matrix of datetime arithmetic operations. Dashes represent operations that are not supported. Table Matrix of Datetime Arithmetic. Examples You can add an interval value expression to a start time. Consider the sample table oe. Oracle Database automatically determines, for any given time zone region, whether daylight saving is in effect and returns local time values accordingly.
The datetime value is sufficient for Oracle to determine whether daylight saving time is in effect for a given region in all cases except boundary cases. A boundary case occurs during the period when daylight saving goes into or comes out of effect. For example, in the US-Pacific region, when daylight saving goes into effect, the time changes from a.
The one hour interval between 2 and 3 a. When daylight saving goes out of effect, the time changes from a. TZR represents the time zone region name in datetime input strings. TZD represents an abbreviated form of the time zone region name with daylight saving information. For a complete listing of the time zone region names in both files, refer to Oracle Database Globalization Support Guide.
Oracle Database Reference for information on the dynamic performance views. The maximum number of digits in field DAY is 6 and the maximum number of digits in the fractional second is 5. The maximum number of digits in all other datetime fields is 2. Interval data types do not have format models. For example, the following examples query the hr.
These data types are intended for binary data or byte strings. For example, you can use LONG RAW to store graphics, sound, documents, or arrays of binary data, for which the interpretation is dependent on the use. In contrast, Oracle Net and the Oracle import and export utilities automatically convert CHAR , VARCHAR2 , and LONG data between different database character sets, if data is transported between databases, or between the database character set and the client character set, if data is transported between a database and a client.
If any of the input characters is not a hexadecimal digit 0 - 9 , A - F , a - f , then an error is reported. If the number of characters is odd, then the result is undefined. BFILE data can be up to 2 64 -1 bytes, although your operating system may impose restrictions on this maximum. When creating a table, you can optionally specify different tablespace and storage characteristics for LOB columns or LOB object attributes from those specified for the table.
LOBs greater than bytes are always stored externally. BFILE data is stored in an external file on the server. You can insert a new row or update an existing row that contains one or more LOB columns or an object with one or more LOB attributes. The locator maintains the directory name and the filename. Binary file LOBs do not participate in transactions and are not recoverable.
Rather, the underlying operating system provides file integrity and durability. The database administrator must ensure that the external file exists and that Oracle processes have operating system read permissions on the file.
You cannot modify or replicate such a file. Oracle provides APIs to access file data. The BLOB data type stores unstructured binary large objects. BLOB objects can be thought of as bitstreams with no character set semantics. BLOB objects have full transactional support. BLOB value manipulations can be committed and rolled back. The CLOB data type stores single-byte and multibyte character data.
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