Abstract
This chapter covers details of expressions in Oracle and the regular expressions catering for text pattern matching and searching. The chapter briefly describes the Oracle Expression Filter. A compound expression is multiple expressions put together with operators. Any built-in or user-defined function comprises a functional expression. Oracle regular expressions conform to and enhance POSIX standards, much like regular expression support in a programming language such as Perl. There are two parts to using regular expressions in Oracle SQL. The first part is the functions that execute regular expression matching, and the second part is the matching patterns. Where the INSTR (REGEXP_INSTR) function retrieves the position of a string, the SUBSTR (REGEXP_SUBSTR) function retrieves a portion of a string. Regular expression functions can be used anywhere a function is used, both built-in and user-defined. Oracle Expression Filter in its simplest form allows application of generically formed WHERE clauses stored in a table. The PL/SQL procedure that uses an Oracle-provided package called DBMS_EXPFIL is described.
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