Improving search by compound indexes. (#3915)

* Improving search by compound indexes.

* Fixing review findings.

* Fixing the index condition handling.

* Adjusting test cases.

* Fixing TableFilter.prepare().

* Adjusting test cases.

* Refactoring the constructors of the IndexCondition class.

* Removing unnecessary TODOs.

* Fixing review findings.

* Introducing the TestCompoundIndexSearch class.

* Preparing IndexCondition to deal with queries where the columns not used in the right order.

* Fixing test errors.

h2/src/main/org/h2/expression/condition/ConditionIn.java

@@ -6,6 +6,8 @@
 package org.h2.expression.condition;
 
 import java.util.ArrayList;
+import java.util.List;
+
 import org.h2.engine.SessionLocal;
 import org.h2.expression.Expression;
 import org.h2.expression.ExpressionColumn;
@@ -165,12 +167,37 @@ public void createIndexConditions(SessionLocal session, TableFilter filter) {
         } else if (left instanceof ExpressionList) {
             ExpressionList list = (ExpressionList) left;
             if (!list.isArray()) {
-                createIndexConditions(filter, list);
+                // First we create a compound index condition.
+                createCompoundIndexCondition(filter);
+                // If there is no compound index, then the TableFilter#prepare() method will drop this condition.
+                // Then we create a unique index condition for each column.
+                createUniqueIndexConditions(filter, list);
+                // If there are two or more index conditions, IndexCursor will only use the first one.
+                // See: IndexCursor#canUseIndexForIn(Column)
             }
         }
     }
 
-    private void createIndexConditions(TableFilter filter, ExpressionList list) {
+    /**
+     * Creates a compound index condition containing every item in the expression list.
+     * @see IndexCondition#getCompoundInList(ExpressionList, List)
+     */
+    private void createCompoundIndexCondition(TableFilter filter) {
+        // We do not check filter here, because the IN condition can contain columns from multiple tables.
+        ExpressionVisitor visitor = ExpressionVisitor.getNotFromResolverVisitor(filter);
+        for (Expression e : valueList) {
+            if (!e.isEverything(visitor)) {
+                return;
+            }
+        }
+        filter.addIndexCondition(IndexCondition.getCompoundInList((ExpressionList) left, valueList));
+    }
+
+    /**
+     * Creates a unique index condition for every item in the expression list.
+     * @see IndexCondition#getInList(ExpressionColumn, List)
+     */
+    private void createUniqueIndexConditions(TableFilter filter, ExpressionList list) {
         int c = list.getSubexpressionCount();
         for (int i = 0; i < c; i++) {
             Expression e = list.getSubexpression(i);

h2/src/main/org/h2/expression/condition/ConditionInConstantSet.java

@@ -6,6 +6,7 @@
 package org.h2.expression.condition;
 
 import java.util.ArrayList;
+import java.util.List;
 import java.util.TreeSet;
 
 import org.h2.engine.SessionLocal;
@@ -139,12 +140,37 @@ public void createIndexConditions(SessionLocal session, TableFilter filter) {
         } else if (left instanceof ExpressionList) {
             ExpressionList list = (ExpressionList) left;
             if (!list.isArray()) {
-                createIndexConditions(filter, list);
+                // First we create a compound index condition.
+                createCompoundIndexCondition(filter);
+                // If there is no compound index, then the TableFilter#prepare() method will drop this condition.
+                // Then we create a unique index condition for each column.
+                createUniqueIndexConditions(filter, list);
+                // If there are two or more index conditions, IndexCursor will only use the first one.
+                // See: IndexCursor#canUseIndexForIn(Column)
             }
         }
     }
 
-    private void createIndexConditions(TableFilter filter, ExpressionList list) {
+    /**
+     * Creates a compound index condition containing every item in the expression list.
+     * @see IndexCondition#getCompoundInList(ExpressionList, List)
+     */
+    private void createCompoundIndexCondition(TableFilter filter) {
+        // We do not check filter here, because the IN condition can contain columns from multiple tables.
+        ExpressionVisitor visitor = ExpressionVisitor.getNotFromResolverVisitor(filter);
+        for (Expression e : valueList) {
+            if (!e.isEverything(visitor)) {
+                return;
+            }
+        }
+        filter.addIndexCondition(IndexCondition.getCompoundInList((ExpressionList) left, valueList));
+    }
+
+    /**
+     * Creates a unique index condition for every item in the expression list.
+     * @see IndexCondition#getInList(ExpressionColumn, List)
+     */
+    private void createUniqueIndexConditions(TableFilter filter, ExpressionList list) {
         int c = list.getSubexpressionCount();
         for (int i = 0; i < c; i++) {
             Expression e = list.getSubexpression(i);