fix(sql): fix backslash escape mechanism in LIKE and ILIKE operator

[SiyaoIsHiding]

Regarding this issue: #2623 (comment) by @bziobrowski
Feature: Enable the backslash escape before wildcards _ and % to make them literal. Even number of backslashes will not make them literal.

Test cases explained as follows:

	Value
Value Stored	The path is \_ignore
Test 1
Pattern Searched	The path is \_ignore
Outcome	Empty
Explanation	A backslash makes the underscore following it become literal
Test 2
Pattern Searched	The path is \\_ignore
Outcome	The path is \_ignore
Explanation	A backslash makes another backslash following it become literal
Test 3
Pattern Searched	The path is \\\_ignore
Outcome	The path is \_ignore
Explanation	Both backslash and underscore become literal

	Value
Test 4
Value stored	\\?\D:\path
Pattern Searched	\\\\_\\%
Outcome	\\?\D:\path
Explanation	Even number of backslashes will not make the wild cards become literal

[bziobrowski]

Please merge from master and fix conflict .

[SiyaoIsHiding]

Thank you very much for your suggestions!

Additionally, I am afraid I do not fully understand your requirement so I wrote and tested three versions that all pass the tests just in case you want me to change to another one.

1. The version in the pull request is what you said "move the whole condition just before the last else".
2. Here is "handle second character not in "_%" in nested if/else ."

        for (int i = 0; i < len; i++) {
            char c = pattern.charAt(i);
            if (c == '\\') {
                if (i + 1 < len){
                    i += 1;
                    c = pattern.charAt(i);
                    if (c == '_' || c == '%') {
                        sink.put(c);
                    } else if(c == '\\'){
                        sink.put("\\\\");
                    } else if ("[](){}.*+?$^|#".indexOf(c) != -1) {
                        sink.put("\\\\\\");
                        sink.put(c);
                    } else  {
                        sink.put("\\\\");
                        sink.put(c);
                    }
                } else {
                    sink.put("\\\\"); // the backslash is the last character
                }
            } else if (c == '_')
                sink.put('.');
            else if (c == '%')
                sink.put(".*?");
            else if ("[](){}.*+?$^|#".indexOf(c) != -1) {
                sink.put("\\");
                sink.put(c);
            } else
                sink.put(c);
        }

3. Here is another version that works:

        for (int i = 0; i < len; i++) {
            char c = pattern.charAt(i);
            if (c == '_')
                sink.put('.');
            else if (c == '%')
                sink.put(".*?");
            else if( c == '\\' && i+1 < len && "_%".indexOf(pattern.charAt(i+1)) != -1){
                i += 1;
                sink.put(pattern.charAt(i));
            }
            else if (c == '\\' && i+1 < len && pattern.charAt(i+1) == '\\'){
                i += 1;
                sink.put("\\\\");
            }
            else if ("[](){}.*+?$^|#\\".indexOf(c) != -1) {
                sink.put("\\");
                sink.put(c);
            } else
                sink.put(c);
        }

[bziobrowski]

What I meant is that logic could be optimized .
Once you find \ there are following options depending on next character :

• if end of string - throw error like PostgreSQL
• if next char is \ - add \
• else print next char (includes '_' and '%' )

[SiyaoIsHiding]

Thx for your detailed explanation. I will modify it today.