Backport #46875 to 23.2: Fix wrong results of some LIKE searches when the LIKE pattern contains quoted non-quotable characters

src/Functions/MatchImpl.h

@@ -23,9 +23,10 @@ namespace ErrorCodes
 namespace impl
 {
 
-/// Is the [I]LIKE expression reduced to finding a substring in a string?
+/// Is the [I]LIKE expression equivalent to a substring search?
 inline bool likePatternIsSubstring(std::string_view pattern, String & res)
 {
+    /// TODO: ignore multiple leading or trailing %
     if (pattern.size() < 2 || !pattern.starts_with('%') || !pattern.ends_with('%'))
         return false;
 
@@ -45,9 +46,25 @@ inline bool likePatternIsSubstring(std::string_view pattern, String & res)
             case '\\':
                 ++pos;
                 if (pos == end)
+                    /// pattern ends with \% --> trailing % is to be taken literally and pattern doesn't qualify for substring search
                     return false;
                 else
-                    res += *pos;
+                {
+                    switch (*pos)
+                    {
+                        /// Known LIKE escape sequences:
+                        case '%':
+                        case '_':
+                        case '\\':
+                            res += *pos;
+                            break;
+                        /// For all other escape sequences, the backslash loses its special meaning
+                        default:
+                            res += '\\';
+                            res += *pos;
+                            break;
+                    }
+                }
                 break;
             default:
                 res += *pos;

tests/queries/0_stateless/25339_like_substring_search_bug.reference

@@ -0,0 +1 @@
+1

tests/queries/0_stateless/25339_like_substring_search_bug.sql

@@ -0,0 +1 @@
+SELECT 'Win\Sys' LIKE '%Win\Sys%';