Optimise LIKE queries for the common cases of '%Foo' and '%Foo%'

h2/src/docsrc/html/changelog.html

@@ -21,6 +21,8 @@ Change Log
 
 <h2>Next Version (unreleased)</h2>
 <ul>
+<li>Optimise LIKE queries for the common cases of '%Foo' and '%Foo%'
+</li>
 <li>Issue #387: H2 MSSQL Compatibility Mode - Support uniqueidentifier
 </li>
 <li>Issue #401: NPE in "SELECT DISTINCT * ORDER BY"

h2/src/main/org/h2/expression/CompareLike.java

@@ -49,6 +49,10 @@ public class CompareLike extends Condition {
     private boolean invalidPattern;
     /** indicates that we can shortcut the comparison and use startsWith */
     private boolean shortcutToStartsWith;
+    /** indicates that we can shortcut the comparison and use endsWith */
+    private boolean shortcutToEndsWith;
+    /** indicates that we can shortcut the comparison and use contains */
+    private boolean shortcutToContains;
 
     public CompareLike(Database db, Expression left, Expression right,
             Expression escape, boolean regexp) {
@@ -179,12 +183,14 @@ public class CompareLike extends Condition {
             return;
         }
         String p = right.getValue(session).getString();
+        if (!isInit) {
             Value e = escape == null ? null : escape.getValue(session);
             if (e == ValueNull.INSTANCE) {
                 // should already be optimized
                 DbException.throwInternalError();
             }
             initPattern(p, getEscapeChar(e));
+        }
         if (invalidPattern) {
             return;
         }
@@ -260,12 +266,42 @@ public class CompareLike extends Condition {
             result = patternRegexp.matcher(value).find();
         } else if (shortcutToStartsWith) {
             result = value.regionMatches(ignoreCase, 0, patternString, 0, patternLength - 1);
+        } else if (shortcutToEndsWith) {
+            result = value.regionMatches(ignoreCase, value.length() - patternLength + 1, patternString, 1, patternLength - 1);
+        } else if (shortcutToContains) {
+            String p = patternString.substring(1, patternString.length() - 1);
+            if (ignoreCase) {
+                result = containsIgnoreCase(value, p);
+            } else {
+                result = value.contains(p);
+            }
         } else {
             result = compareAt(value, 0, 0, value.length(), patternChars, patternTypes);
         }
         return ValueBoolean.get(result);
     }
 
+    private static boolean containsIgnoreCase(String src, String what) {
+        final int length = what.length();
+        if (length == 0)
+            return true; // Empty string is contained
+
+        final char firstLo = Character.toLowerCase(what.charAt(0));
+        final char firstUp = Character.toUpperCase(what.charAt(0));
+
+        for (int i = src.length() - length; i >= 0; i--) {
+            // Quick check before calling the more expensive regionMatches() method:
+            final char ch = src.charAt(i);
+            if (ch != firstLo && ch != firstUp)
+                continue;
+
+            if (src.regionMatches(true, i, what, 0, length))
+                return true;
+        }
+
+        return false;
+    }
+
     private boolean compareAt(String s, int pi, int si, int sLen,
             char[] pattern, int[] types) {
         for (; pi < patternLength; pi++) {
@@ -390,6 +426,32 @@ public class CompareLike extends Condition {
             }
             if (maxMatch == patternLength - 1 && patternTypes[patternLength - 1] == ANY) {
                 shortcutToStartsWith = true;
+                return;
+            }
+        }
+        // optimizes the common case of LIKE '%foo'
+        if (compareMode.getName().equals(CompareMode.OFF) && patternLength > 1) {
+            if (patternTypes[0] == ANY) {
+                int maxMatch = 1;
+                while (maxMatch < patternLength && patternTypes[maxMatch] == MATCH) {
+                    maxMatch++;
+                }
+                if (maxMatch == patternLength) {
+                    shortcutToEndsWith = true;
+                    return;
+                }
+            }
+        }
+        // optimizes the common case of LIKE '%foo%'
+        if (compareMode.getName().equals(CompareMode.OFF) && patternLength > 2) {
+            if (patternTypes[0] == ANY) {
+                int maxMatch = 1;
+                while (maxMatch < patternLength && patternTypes[maxMatch] == MATCH) {
+                    maxMatch++;
+                }
+                if (maxMatch == patternLength - 1 && patternTypes[patternLength - 1] == ANY) {
+                    shortcutToContains = true;
+                }
             }
         }
     }