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Substrings in ZMSQL

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maurobio:
Dear ALL,

Many dialects of SQL (MySQL, SQLite, etc.) have a handy SUBSTR() function which extract a substring from a string (starting at any position), for example:


--- Code: Pascal  [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---SELECT SUBSTR(CustomerName, 2, 5) AS ExtractString FROM Customers;
However, the ZMSQL library (https://wiki.freepascal.org/ZMSQL) offers two rather unusual variations of this function, as follows:


--- Quote ---substr_after(source, substring) Returns the part of source that comes after substring. If substring is not found an empty string is returned.

substr_before(source, substring) Returns the part of source that comes before substring. If substring is not found an empty string is returned.

--- End quote ---
I do not understand how these functions work and have not been able to find any examples. Could some one provides me with a few hints?

Thanks in advance!

With best wishes,

paweld:
mid(expression, from, count) : https://github.com/git-bee/janSQL/blob/master/doc/6_functions.md#64-string-functions

--- Code: SQL  [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---SELECT string_col, mid(string_col, 2, 5) FROM TABLE

maurobio:
Dear @paweld,

Thanks a lot, it is now clear and it works fine!

With best wishes,

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