Month: March 2015

Oracle character set conversion downgrade checkup with utl_i18n


Doing an export/import or a ctas or an oci/jdbc client action into a database that has smaller sized character set, multi- to single-byte for example, will raise the problem of information loss in terms of character data. The information loss, however, is not limited to loosing one or the other character. Some characters may also become replaced by a default or a best guess replacement character in the target character set automatically.
Profound analysis of the outcome of the character set conversion might also cause difficulties when only the source database is already available and just an estimation of the information loss is what you need. You may come up with good old convert() to execute an input/output compare but aside from using convert() is discouraged with the latest releases of Oracle, convert() will also fracture the strings on input as soon as the first multibyte character appears. convert() will alert you of some problem but it will not tell you why or even better: what character is (first) the stumbling block.

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Bottom-up hierarchical root path query recipe in oracle


Oracle supports hierarchical querying since long and has continuously extended the set of available features, i.e. pseudo-columns, path generation, leaf sorting by name, etc. With 11gR2, Oracle even complements with the ANSI SQL standard approach: the CONNECT BY syntax for hierarchical querying that can now be replaced by the ANSI SQL standard Recursive Subquery Factoring clause, see Oracle RDBMS 11gR2 – goodbye Connect By or: the end of hierarchical querying as we know it for more information.
However, talking about hierarchical querying with Oracle always implies a top-down traversion (see another post on that subject from a couple of years ago that did not provided a PL/SQL ready solution as Implementing bottom-up path traversal for hierarchical tables). You start (START WITH) at some root node(s) of your choice and dive into the branches and leaves (CONNECT BY) by connecting child-nodes to parent-nodes until the final leaf has been consumed (check CONNECT_BY_ISLEAF) or a certain LEVEL has been reached by filter. There is tons of examples out there showing this in action. Here is just some simple code example to start off with, employing SYS_CONNECT_BY_PATH, introducing root- to leaf-node path generation over the child-to-parent relationship between columns T.P_ID and T.ID.

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