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Relational operators
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• The string_constant may be a string constant or a scalar function call.
• The escape_character must be a one character string constant.
• A percent sign ( % ) in the pattern matches zero or more characters of the column string.
• An underscore symbol ( _ ) in the pattern matches any single character of the column
string.
• The LIKE predicate is multi-byte enabled. The string_constant and the
escape_character may contain multi-byte characters, and the escape_character can be
a multi-byte character. A percent sign ( % ) or an underscore ( _ ) in the string_constant
can represent a multi-byte character. However, the percent sign or underscore itself must
be the single-byte ASCII encoding.
Example This example illustrates three ways to use the LIKE predicate:
cust_name LIKE ’%Computer%’
cust_name LIKE ’___’
item_name LIKE ’%\_%’ ESCAPE ’\’
In the first LIKE clause, for all strings with the substring ’Computer’ the predicate evaluates to
true. In the second LIKE clause, for all strings which are exactly three characters long the
predicate evaluates to true. In the third LIKE clause the backslash character ( \ ) is specified as
the escape character, which means that the special interpretation given to the underscore
character ( _ ) is disabled. The pattern evaluates to TRUE if the item_name column has embedded
underscore characters.
EXISTS Predicate
The EXISTS predicate can be used to check for the existence of specific rows. The
query_expression returns rows rather than values. The predicate evaluates to true if the number
of rows returned by the query_expression is nonzero. This is the syntax for an EXISTS predicate:
Syntax
EXISTS (query_expression)
Example In this example, the predicate evaluates to true if the specified customer has any orders:
EXISTS (SELECT * FROM order_tbl
WHERE order_tbl.custid = ’888’ ;)
IN Predicate
The IN predicate can be used to compare a value with a set of values. If an IN predicate specifies
a query expression, then the result table it returns can contain only a single column. This is the
syntax for an IN predicate: