korlov42 commented on code in PR #6996:
URL: https://github.com/apache/ignite-3/pull/6996#discussion_r2541556649
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modules/sql-engine/src/main/java/org/apache/ignite/internal/sql/engine/exec/exp/IgniteSqlFunctions.java:
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@@ -761,4 +761,196 @@ private static long divide(long p, long q, RoundingMode
mode) {
return increment ? div + signum : div;
}
+
+ /**
+ * Computes the next lexicographically greater string by incrementing the
rightmost character that is not at its maximum value.
+ *
+ * <p>This method is primarily used in conjunction with {@link
#findPrefix(String, String)} to create upper bounds for efficient
+ * range scans. Given a prefix extracted from a LIKE pattern, this method
produces the smallest string that is lexicographically greater
+ * than the prefix, enabling queries like {@code WHERE key >= prefix AND
key < nextGreaterPrefix}.
+ *
+ * <p>If all characters are at maximum value ({@value
Character#MAX_VALUE}), the method returns {@code null} because no greater string
+ * exists within the Unicode character space.
+ *
+ * <p>Basic examples:
+ * <pre>
+ * nextGreaterPrefix("abc") → "abd"
+ * nextGreaterPrefix("test") → "tesu"
+ * nextGreaterPrefix("user") → "uses"
+ * nextGreaterPrefix("a") → "b"
+ * nextGreaterPrefix("z") → "{"
+ * nextGreaterPrefix("9") → ":"
+ * </pre>
+ *
+ * <p>Examples with maximum values:
+ * <pre>
+ * nextGreaterPrefix("abc\uFFFF") → "abd" (skip max char,
increment 'c')
+ * nextGreaterPrefix("a\uFFFF\uFFFF") → "b" (skip two max chars,
increment 'a')
+ * nextGreaterPrefix("test\uFFFF") → "tesu" (skip max char,
increment 't')
+ * nextGreaterPrefix("\uFFFF") → null (cannot increment)
+ * nextGreaterPrefix("\uFFFF\uFFFF") → null (all chars at max)
+ * </pre>
+ *
+ * <p>Edge cases:
+ * <pre>
+ * nextGreaterPrefix(null) → null (null input)
+ * nextGreaterPrefix("") → null (empty string, no
chars to increment)
+ * nextGreaterPrefix("abc\uFFFF\uFFFF") → "abd" (truncates all
trailing max values)
+ * </pre>
+ *
+ * <p>Properties:
+ * <ul>
+ * <li>The result is always the <em>smallest</em> string greater than
the input</li>
+ * <li>For any valid input {@code s}, {@code
nextGreaterPrefix(s).compareTo(s) > 0}</li>
+ * <li>The result may be shorter than the input (trailing max-value
chars are removed)</li>
+ * <li>Trailing {@code \uFFFF} characters are effectively truncated</li>
+ * </ul>
+ *
+ * @param prefix The string to increment. If {@code null}, returns {@code
null}.
+ * @return A next lexicographically greater string, or {@code null} if the
input is {@code null}, empty, or consists entirely of
+ * maximum-value characters ({@code \uFFFF}). The returned string
is guaranteed to be the smallest string greater than the
+ * input.
+ */
+ public static @Nullable String nextGreaterPrefix(@Nullable String prefix) {
+ if (prefix == null) {
+ return null;
+ }
+
+ // Try to increment characters from right to left
+ for (int i = prefix.length() - 1; i >= 0; i--) {
+ char c = prefix.charAt(i);
+
+ // Check if we can increment this character
+ if (c < Character.MAX_VALUE) {
+ // Increment and return
+ return prefix.substring(0, i) + ((char) (c + 1));
+ }
+
+ // This character is already max, continue to previous character
+ }
+
+ // All characters are at maximum value
+ return null; // Given prefix is the greatest.
+ }
+
+ /**
+ * Extracts the literal prefix from a SQL LIKE pattern by identifying all
characters before the first unescaped wildcard.
+ *
+ * <p>This method processes SQL LIKE patterns containing wildcards ({@code
%} for any sequence, {@code _} for single character) and
+ * returns the constant prefix that can be used for optimized range scans.
+ *
+ * <p>When an escape character is provided, it allows wildcards to be
treated as literal characters. The escape character itself can
+ * also be escaped to include it literally in the prefix.
+ *
+ * <p>Examples without escape character:
+ * <pre>
+ * findPrefix("user%", null) → "user"
+ * findPrefix("admin_123", null) → "admin"
+ * findPrefix("test", null) → "test"
+ * findPrefix("%anything", null) → ""
Review Comment:
this case is similar to this one: `* findPrefix("admin_123", null) →
"admin"`. Updated the javadoc
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