Alternative for nesting REPLACE()?
(1) By anonymous on 2020-10-04 13:35:55 [link]
Is there an alternative for nesting REPLACE() functions when replacing multiple strings? Even a simple removal of CR and LF results in REPLACE(REPLACE(data,CHAR(13),'~'),CHAR(10),'~'). Now imagine a dozen replacements .....
(2) By Simon Slavin (slavin) on 2020-10-04 15:11:10 in reply to 1
Write your own function. <http://www.sqlite.org/c3ref/create_function.html>
(3) By Donald Griggs (dfgriggs) on 2020-10-04 16:07:55 in reply to 1 [link]
Bedsides Simon's good suggestion of writing a custom function, you might consider whether the expected rows would fit in cache, and, if so, a series of separate UPDATE's enclosed in a transaction might be sufficiently speedy. -- or, a CTE can be used with a table of search/replace strings. -- or would just formatting a big UPDATE not meet your need? I imagine a dozen replacements as something like: <code> UPDATE myTable SET data = REPLACE(REPLACE(REPLACE(REPLACE(REPLACE(REPLACE( REPLACE(REPLACE(REPLACE(REPLACE(REPLACE(REPLACE( data, CHAR(13), '~' ) ,CHAR(10), '~' ) ,'division', 'unity' ) ,'fear', 'serenity' ) ,'greed', 'charity' ) ,'travesties', 'justice' ) ,'suspicion', 'empathy' ) ,'depression', 'joy' ) ,'hate', 'love' ) ,'poverty', 'sharing' ) ,'xenophobia', 'friendship') ,'copyright', 'blessing' ) ; </code> Donald
(4) By anonymous on 2020-10-04 20:25:32 in reply to 1 [link]
Have a small table with the replacements and use a simple `SELECT` to get the corresponding value. I think this is safer because it will only replace a value once. The nested `REPLACE` runs the risk of accidentally replacing what's already replaced, unless that's a requirement in some cases. For example, changing 'dogs' to 'cats' and 'cats' to 'mice' with nested `REPLACE` could end up with just 'mice' instead of 'cats' and 'mice'.
(5) By anonymous on 2020-10-31 22:51:57 in reply to 2 [link]
(6) By Simon Slavin (slavin) on 2020-11-01 08:53:34 in reply to 4 [link]
Starting with that idea of a small table with the replacements, might it be possible to do this using a CTE ?
(7) By anonymous on 2020-11-01 22:05:50 in reply to 3 [link]
Unfortunately you are barking up the wrong tree...... This was never about UPDATEs - the usage of REPLACE is intended for cleaning up output and/or fixing issues with UTF8 and ORDER. And nesting REPLACE does not work - by the time I had reached the required level of nesting I was rewarded with a stack overflow.
(8) By jake on 2020-11-02 10:03:58 in reply to 2 [link]
Here's an [aggregate replace function](https://github.com/jakethaw/replace_agg) I wrote several years ago. Disclaimer: I was relatively new to C when this was written, so no guarantees except for the fact that I've used it over the years and have not encountered any issues.