Character large object
Encyclopedia
A Character Large Object (or CLOB) is a collection of character
data
in a database management system
, usually stored in a separate location that is referenced in the table itself. Oracle
and IBM DB2
provide a construct explicitly named CLOB, and the majority of other database systems support some form of the concept, often labeled as text, memo or long character fields.
CLOBs usually have very high size limits, on the order of 2GB or more. The tradeoff for the capacity is usually limited access methods. In particular, some database systems limit certain SQL
clauses, such as LIKE or SUBSTRING from being used on CLOBs.
Alternative methods of accessing the data are often provided, including means of extracting or inserting ranges of data from the CLOB.
Database systems vary in their storage patterns for CLOBs. Some systems always store CLOBs as a reference to out-of-table data, while others store small CLOBs in-table, changing their storage patterns when the size of the data grows beyond a threshold. Other systems are configurable in their behavior.
CLOBs are distinguished from BLOB
s by having a specified character encoding
.
Character (computing)
In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language....
data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
in a database management system
Database management system
A database management system is a software package with computer programs that control the creation, maintenance, and use of a database. It allows organizations to conveniently develop databases for various applications by database administrators and other specialists. A database is an integrated...
, usually stored in a separate location that is referenced in the table itself. Oracle
Oracle database
The Oracle Database is an object-relational database management system produced and marketed by Oracle Corporation....
and IBM DB2
IBM DB2
The IBM DB2 Enterprise Server Edition is a relational model database server developed by IBM. It primarily runs on Unix , Linux, IBM i , z/OS and Windows servers. DB2 also powers the different IBM InfoSphere Warehouse editions...
provide a construct explicitly named CLOB, and the majority of other database systems support some form of the concept, often labeled as text, memo or long character fields.
CLOBs usually have very high size limits, on the order of 2GB or more. The tradeoff for the capacity is usually limited access methods. In particular, some database systems limit certain SQL
SQL
SQL is a programming language designed for managing data in relational database management systems ....
clauses, such as LIKE or SUBSTRING from being used on CLOBs.
Alternative methods of accessing the data are often provided, including means of extracting or inserting ranges of data from the CLOB.
Database systems vary in their storage patterns for CLOBs. Some systems always store CLOBs as a reference to out-of-table data, while others store small CLOBs in-table, changing their storage patterns when the size of the data grows beyond a threshold. Other systems are configurable in their behavior.
CLOBs are distinguished from BLOB
Blob
- In biology :* Blob , sections of the visual cortex where groups of color-sensitive neurons assemble* Globster, an unidentified organic mass that washes up on the shoreline of an ocean or other body of water...
s by having a specified character encoding
Character encoding
A character encoding system consists of a code that pairs each character from a given repertoire with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the transmission of data through telecommunication networks or storage of text in...
.