替换为Regexp无法正常工作

Question

I want to replace a query string like this:

SELECT abc,def,ghi,jhk FROM table....

with

SELECT X FROM table....

this should be quite easy and i get the regexp replace to work as expected, but i cant get my expression right. This is what i have:

rgx = new Regex("SELECT*.FROM");
data = rgx.Replace(data, "SELECT X FROM");

It also does not work in the online evaluator i tried, but i have no clue how it has to be then. And how do i get a modifier in there? I think it should be ungreedy.

I know that this whole thing might seem useless but this is exactly what i want and need to do.

Answer 1

You mixed up the * and .

Also you might want to add some spaces in there, otherwise the regex would also match SELECTFOOBARFROM .

Further more (assuming that C#'s Regexes support non-greediness) I'd make the wildcard non-greedy via a trailing ? .
Right now your regex is greedy. As a result your current regex would change this:

SELECT Foo FROM Bar WHERE Baz IN (SELECT FooID FROM Bar WHERE Foo = 'Foo')

into this:

SELECT X FROM Bar WHERE Foo = 'Foo')

while the correct result would have been this:

SELECT X FROM Bar WHERE Baz IN (SELECT X FROM Bar WHERE Foo = 'Foo')

Ergo, go with this instead:

rgx = new Regex("SELECT .*? FROM");

Answer 2

You want:

rgx = new Regex("SELECT.*FROM");

Note the order of the . and the *.

the * is basically a modifier for whatever character or group it follows so in yours you were matching 0 or more of the letter T instead of 0 or more of any character.