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Oracle Corporation's Oracle Ultra Search (also known as Ultrasearch) allows the generation of indexes to textual material stored (for example) on web-servers, file-servers, databases and mail-systems. It uses crawlers and Oracle Text utilities to build its indexes, which it then makes available within an Oracle database.
Oracle Corporation introduced Oracle ConText first as a software option, then as an Oracle data cartridge (a server-based software module) for text retrieval when it released version 8 of the Oracle database in 1997. It used the default schema CTXSYS and the default tablespace DRSYS.
No index The optimizer must use a full table scan since no index exists. Small number of rows The cost of full table scan is less than index range scan due to small table. When query processed SELECT COUNT(*), nulls existed in the column The query is counting the number of null columns in a typical index. However, SELECT COUNT(*) can't count ...
A simple and inefficient way to see where one string occurs inside another is to check at each index, one by one. First, we see if there is a copy of the needle starting at the first character of the haystack; if not, we look to see if there's a copy of the needle starting at the second character of the haystack, and so forth.
The DUAL table is a special one-row, one-column table present by default in Oracle and other database installations. In Oracle, the table has a single VARCHAR2(1) column called DUMMY that has a value of 'X'. It is suitable for use in selecting a pseudo column such as SYSDATE or USER.
Note (6): Can be implemented using Function-based Indexes in Oracle 8i and higher, but the function needs to be used in the sql for the index to be used. Note (7): A PostgreSQL functional index can be used to reverse the order of a field. Note (10): B+ tree and full-text only for now.
In text retrieval, full-text search refers to techniques for searching a single computer-stored document or a collection in a full-text database.Full-text search is distinguished from searches based on metadata or on parts of the original texts represented in databases (such as titles, abstracts, selected sections, or bibliographical references).
Instead, they take advantage of the fact that the actual data is always in main memory together with the index so that they just contain pointers to the actual data fields. The 'T' in T-tree refers to the shape of the node data structures in the original paper which first described this type of index. [1]