MATCHES and LIKE

Informix®

Informix supports MATCHES and LIKE operators in SQL statements.

MATCHES expects * and ? wild-card characters, while LIKE uses the % and _ wild-cards as equivalents.

( col MATCHES 'Smi*' AND col NOT MATCHES 'R?x' )
( col LIKE 'Smi%' AND col NOT LIKE 'R_x' )

MATCHES accepts also brackets notation, to specify a set of matching characters at a given position:

( col MATCHES '[Pp]aris' )
( col MATCHES '[0-9][a-z]*' )

PostgreSQL

PostgreSQL supportes the LIKE operator, and the ~ operator wich expects regular expressions as follows: ( col ~ 'a.*' )

PostgreSQL provides the SIMILAR TO opertator, allowing character range specification as the Informix MATCHES operator:

( col SIMILAR TO '[Pp]ar%' )

Important:

With PostgreSQL, columns defined as CHAR(N) are blank padded, and trailing blanks are significant in the LIKE expressions. As result, with a CHAR(5) value such as 'abc ' (with 2 trailing blanks), the expression (colname LIKE 'ab_') will not match. To workaround this behavior, you can do (RTRIM(colname) LIKE 'pattern'). However, consider adding the condition AND (colname LIKE 'patten%') to force the DB server to optimize the query of the column is indexed. The CONSTRUCT instruction uses this technique when the entered criteria does not end with a * star wildcard.

Solution

The database driver converts Informix MATCHES expressions to LIKE expressions, when no [ ] bracket character ranges are used in the MATCHES operand. When character ranges are used, the driver converts to a PostgreSQL SIMILAR TO expression, to find the same values as with the Informix MATCHES operator.

Important:

Only [NOT] MATCHES followed by a search pattern provided as a string literal can be converted by ODI drivers. A [NOT] MATCHES followed by a ? question mark parameter place holder is not translated!

For maximum portability, consider replacing the MATCHES expressions to LIKE expressions in all SQL statements of your programs.

With PostgreSQL, trailing blanks are significant when comparing CHAR() columns with LIKE or SIMILAR TO expressions. Consider adding an ending * when comparing with CHAR() columns. This is not needs for VARCHAR() columns.

Avoid using CHAR(N) types for variable length character data (such as name, address).