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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2008-01-23 19:51:29 +0000 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2008-01-23 19:51:29 +0000 |
| commit | 216e63bbce59aba7ab8e0f96219c7ec0a120207d (patch) | |
| tree | 835df8600fc95ff716f649e4525fe8d626b8093b | |
| parent | 8984c8bbe237d16204019c2803343dc6d16a9d0e (diff) | |
| download | postgresql-216e63bbce59aba7ab8e0f96219c7ec0a120207d.tar.gz postgresql-216e63bbce59aba7ab8e0f96219c7ec0a120207d.zip | |
Avoid mathematical inconsistency in example about avoiding division by
zero with a CASE expression. Per gripe from Russell Smith.
| -rw-r--r-- | doc/src/sgml/syntax.sgml | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml index c49d81b7f90..8761b6e1da7 100644 --- a/doc/src/sgml/syntax.sgml +++ b/doc/src/sgml/syntax.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.120 2007/12/11 18:30:20 mha Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.121 2008/01/23 19:51:29 tgl Exp $ --> <chapter id="sql-syntax"> <title>SQL Syntax</title> @@ -1740,15 +1740,15 @@ SELECT somefunc() OR true; used. For example, this is an untrustworthy way of trying to avoid division by zero in a <literal>WHERE</> clause: <programlisting> -SELECT ... WHERE x <> 0 AND y/x > 1.5; +SELECT ... WHERE x > 0 AND y/x > 1.5; </programlisting> But this is safe: <programlisting> -SELECT ... WHERE CASE WHEN x <> 0 THEN y/x > 1.5 ELSE false END; +SELECT ... WHERE CASE WHEN x > 0 THEN y/x > 1.5 ELSE false END; </programlisting> A <literal>CASE</> construct used in this fashion will defeat optimization attempts, so it should only be done when necessary. (In this particular - example, it would be best to sidestep the problem by writing + example, it would be better to sidestep the problem by writing <literal>y > 1.5*x</> instead.) </para> </sect2> |