On Thu, Feb 09, 2012 at 09:34:45AM +0000, Michael Meeks wrote: > Out of interest, do databasen use 'not zero' for their true state (as > C/C++ etc.) ? or always exactly 1 ?
In the SQL standard, the only (explicit, with a cast)s data conversion specified for booleans are to/from the strings 'TRUE' and 'FALSE' and 'UNKNOWN' (a synonym for NULL in boolean context), which correspond to the literals. Anything else is database-specific and can be an error. MySQL does not really have a boolean datatype; it is a synonym for "tinyint" (8 bit integer). In tests (when a "truth value" is required), anything not-zero is true (except NULL), but TRUE is the constant one. So SELECT * FROM table WHERE boolColumn=TRUE and SELECT * FROM table WHERE boolColumn do not give the same results. They are, respectively: SELECT * FROM table WHERE boolColumn=1 and SELECT * FROM table WHERE boolColumn<>0 "boolColumn" can be any integer column. PostgreSQL has a boolean datatype, and there is no automatic conversion between integers and booleans: => SELECT 0=FALSE; ERROR: operator does not exist: integer = boolean => SELECT * FROM table WHERE integerColumn; ERROR: argument of WHERE must be type boolean, not type integer But they can be explicitly casted and then TRUE=>1, and non-zero=>TRUE. Interestingly, you can cast a boolean to a 32-bit integer, but not to a 16-bit or 64-bit integer... And vice-versa: you can cast a 32-bit integer to a boolean, but not a 16 or 64-bit integer to a boolean. A truth value (result of test) is basically a boolean. -- Lionel _______________________________________________ LibreOffice mailing list LibreOffice@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/libreoffice
