4 Special Characters in Oracle Text Queries

4.1 Grouping Characters

The grouping characters control operator precedence by grouping query terms and operators in a query expression. The grouping characters are described in Table 4-1.

The beginning of a group of terms and operators is indicated by an open character from one of the sets of grouping characters. The ending of a group is indicated by the occurrence of the appropriate close character for the open character that started the group. Between the two characters, other groups may occur.

For example, the open parenthesis indicates the beginning of a group. The first close parenthesis encountered is the end of the group. Any open parentheses encountered before the close parenthesis indicate nested groups.

4.2 Escape Characters

To query on words or symbols that have special meaning in query expressions such as and & or| accum, you must escape them. There are two ways to escape characters in a query expression, as described in Table 4-2.

In the following examples, an escape sequence is necessary because each expression contains a Text operator or reserved symbol:

'high\-voltage'
'{high-voltage}'

'XY\&Z'
'{XY&Z}'

In the first example, the query matches high-voltage or high voltage.

Note that in the second example, a query on XY&Z will return 'XY Z', 'XY-Z', 'XY*Z', and so forth, as well as 'XY&Z'. This is because non-alphabetic characters are treated as whitespace (so XY&Z is treated as 'XY Z'). To match only XY&Z, you must declare & as a printjoin. (If you do, however, XY&Z will not match 'XY & Z'.) For more on printjoins, see BASIC_LEXER.

4.3 Reserved Words and Characters

Table 4-3 lists the Oracle Text reserved words and characters that must be escaped when you want to search them in CONTAINS queries. Refer to Table 4-2 for the rule for when to use braces {} or the backslash \ for the escape sequence.