On 11/11/2017 8:55 PM, Balaji Ramanathan wrote:
3. When there is a mathematical expression after the string, I get a 0. My string is nowhere to be seen in the output SQLite> select '- '||cast(-1.5 as integer)*-1 0
|| has the highest precedence. Your expression is interpreted as ( '- '||cast(-1.5 as integer) ) * -1 . The string produced by the stuff in parentheses doesn't look like a valid number, and so becomes 0 when coerced to the same. Basically, you are doing select 'foobar' * -1
4. But when I add 1 instead of multiplying, it produces output that seems to evaluate everything before the addition to zero SQLite> select '- '||cast(-1.5 as integer)+1 1
0 * -1 == 0 0 + 1 == 1
5. Enclosing the mathematical expression in a printf produces the correct output SQLite> select '- '|| printf(cast(-1.5 as integer)*-1) - 1
So would enclosing in parentheses. The point is not printf() call, but changing the order of evaluation.
6. If the output starts with a number, then it doesn't seem to matter what follows. Notice that the last part of the expression below is the same as the expression in query number 3 above, but it works fine now whereas previously it produced a zero as the output SQLite> select cast(1.5 as integer)||'-'||(cast(-1.5 as integer)*-1) 1-1
The last part is parenthesized here, whereas it wasn't in prior examples. That makes all the difference.
I am sure it has something to do with order of operations and the affinity of the operands, but can someone give me a summary that I can understand readily? The only mentions of the "||" operator on the SQLite website ( https://sqlite.org/lang_expr.html) don't really explain what is going on in the above examples.
The part of the article you quote that you seem to overlook is "in order from highest to lowest precedence" -- Igor Tandetnik _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
