Experimental feature to support nested joins.

h2/src/main/org/h2/command/Parser.java

@@ -1229,7 +1229,7 @@ public class Parser {
                 if (readIf("ON")) {
                     on = readExpression();
                 }
-                newTop.addJoin(top, true, on);
+                newTop.addJoin(top, true, fromOuter, on);
                 top = newTop;
                 last = newTop;
             } else if (readIf("LEFT")) {
@@ -1241,10 +1241,10 @@ public class Parser {
                 if (readIf("ON")) {
                     on = readExpression();
                 }
-                top.addJoin(join, true, on);
+                top.addJoin(join, true, fromOuter, on);
                 last = join;
             } else if (readIf("FULL")) {
-                throw this.getSyntaxError();
+                throw getSyntaxError();
             } else if (readIf("INNER")) {
                 read("JOIN");
                 TableFilter join = readTableFilter(fromOuter);
@@ -1253,7 +1253,11 @@ public class Parser {
                 if (readIf("ON")) {
                     on = readExpression();
                 }
-                top.addJoin(join, fromOuter, on);
+                if (SysProperties.NESTED_JOINS) {
+                    top.addJoin(join, false, fromOuter, on);
+                } else {
+                    top.addJoin(join, fromOuter, fromOuter, on);
+                }
                 last = join;
             } else if (readIf("JOIN")) {
                 TableFilter join = readTableFilter(fromOuter);
@@ -1262,12 +1266,20 @@ public class Parser {
                 if (readIf("ON")) {
                     on = readExpression();
                 }
-                top.addJoin(join, fromOuter, on);
+                if (SysProperties.NESTED_JOINS) {
+                    top.addJoin(join, false, fromOuter, on);
+                } else {
+                    top.addJoin(join, fromOuter, fromOuter, on);
+                }
                 last = join;
             } else if (readIf("CROSS")) {
                 read("JOIN");
                 TableFilter join = readTableFilter(fromOuter);
-                top.addJoin(join, fromOuter, null);
+                if (SysProperties.NESTED_JOINS) {
+                    top.addJoin(join, false, fromOuter, null);
+                } else {
+                    top.addJoin(join, fromOuter, fromOuter, null);
+                }
                 last = join;
             } else if (readIf("NATURAL")) {
                 read("JOIN");
@@ -1296,7 +1308,11 @@ public class Parser {
                         }
                     }
                 }
-                top.addJoin(join, fromOuter, on);
+                if (SysProperties.NESTED_JOINS) {
+                    top.addJoin(join, false, fromOuter, on);
+                } else {
+                    top.addJoin(join, fromOuter, fromOuter, on);
+                }
                 last = join;
             } else {
                 break;
@@ -1543,6 +1559,12 @@ public class Parser {
         command.addTableFilter(top, true);
         boolean isOuter = false;
         while (true) {
+            for (TableFilter n = top.getNestedJoin(); n != null; n = n.getNestedJoin()) {
+                command.addTableFilter(n, false);
+                for (TableFilter j = n.getJoin(); j != null; j = j.getJoin()) {
+                    command.addTableFilter(j, false);
+                }
+            }
             TableFilter join = top.getJoin();
             if (join == null) {
                 break;
@@ -1810,7 +1832,7 @@ public class Parser {
                                 int idx = filters.indexOf(rightFilter);
                                 if (idx >= 0) {
                                     filters.remove(idx);
-                                    leftFilter.addJoin(rightFilter, true, r);
+                                    leftFilter.addJoin(rightFilter, true, false, r);
                                 } else {
                                     rightFilter.mapAndAddFilter(r);
                                 }

h2/src/main/org/h2/command/dml/Optimizer.java

@@ -232,7 +232,7 @@ public class Optimizer {
         TableFilter[] f2 = bestPlan.getFilters();
         topFilter = f2[0];
         for (int i = 0; i < f2.length - 1; i++) {
-            f2[i].addJoin(f2[i + 1], false, null);
+            f2[i].addJoin(f2[i + 1], false, false, null);
         }
         for (TableFilter f : f2) {
             PlanItem item = bestPlan.getItem(f);

h2/src/main/org/h2/command/dml/Select.java

@@ -846,8 +846,14 @@ public class Select extends Query {
         topTableFilter = optimizer.getTopFilter();
         double planCost = optimizer.getCost();
         
-        TableFilter f = topTableFilter;
-        while (f != null) {
+        setEvaluatableRecursive(topTableFilter);
+
+        topTableFilter.prepare();
+        return planCost;
+    }
+    
+    private void setEvaluatableRecursive(TableFilter f) {
+        for (; f != null; f = f.getJoin()) {
             f.setEvaluatable(f, true);
             if (condition != null) {
                 condition.setEvaluatable(f, true);
@@ -879,10 +885,11 @@ public class Select extends Query {
             for (Expression e : expressions) {
                 e.setEvaluatable(f, true);
             }
-            f = f.getJoin();
+            TableFilter n = f.getNestedJoin();
+            if (n != null) {
+                setEvaluatableRecursive(n);
+            }
         }
-        topTableFilter.prepare();
-        return planCost;
     }
 
     public String getPlanSQL() {

h2/src/main/org/h2/constant/SysProperties.java

@@ -386,6 +386,12 @@ public class SysProperties {
      */
     public static final int MIN_WRITE_DELAY = getIntSetting("h2.minWriteDelay", 5);
     
+    /**
+     * System property <code>h2.nestedJoins</code> (default: false).<br />
+     * Whether nested joins should be supported.
+     */
+    public static final boolean NESTED_JOINS = getBooleanSetting("h2.nestedJoins", false);
+
     /**
      * System property <code>h2.nioLoadMapped</code> (default: false).<br />
      * If the mapped buffer should be loaded when the file is opened.

h2/src/main/org/h2/table/PlanItem.java

@@ -21,6 +21,7 @@ public class PlanItem {
 
     private Index index;
     private PlanItem joinPlan;
+    private PlanItem nestedJoinPlan;
 
     void setIndex(Index index) {
         this.index = index;
@@ -34,8 +35,16 @@ public class PlanItem {
         return joinPlan;
     }
     
+    PlanItem getNestedJoinPlan() {
+        return nestedJoinPlan;
+    }
+
     void setJoinPlan(PlanItem joinPlan) {
         this.joinPlan = joinPlan;
     }
 
+    void setNestedJoinPlan(PlanItem nestedJoinPlan) {
+        this.nestedJoinPlan = nestedJoinPlan;
+    }
+
 }

h2/src/main/org/h2/table/TableFilter.java

@@ -70,8 +70,22 @@ public class TableFilter implements ColumnResolver {
     private SearchRow currentSearchRow;
     private Row current;
     private int state;
+    
+    /**
+     * The joined table (if there is one).
+     */
     private TableFilter join;
-    private boolean outerJoin;
+    
+    /**
+     * Whether this table is an outer join.
+     */
+    private boolean joinOuter;
+    
+    /**
+     * The nested joined table (if there is one).
+     */
+    private TableFilter nestedJoin;
+    
     private ArrayList<Column> naturalJoinColumns;
     private boolean foundOne;
     private Expression fullCondition;
@@ -153,6 +167,14 @@ public class TableFilter implements ColumnResolver {
             // x (x.a=10); y (x.b=y.b) - see issue 113
             item.cost -= item.cost * indexConditions.size() / 100 / level;
         }
+        if (nestedJoin != null) {
+            setEvaluatable(nestedJoin);
+            item.setNestedJoinPlan(nestedJoin.getBestPlanItem(s, level));
+            int todoNestJoinCostWrong;
+            // TODO optimizer: calculate cost of a join: should use separate
+            // expected row number and lookup cost
+            item.cost += item.cost * item.getNestedJoinPlan().cost;
+        }
         if (join != null) {
             setEvaluatable(join);
             item.setJoinPlan(join.getBestPlanItem(s, level));
@@ -170,6 +192,10 @@ public class TableFilter implements ColumnResolver {
             if (e != null) {
                 e.setEvaluatable(this, true);
             }
+            TableFilter n = join.getNestedJoin();
+            if (n != null) {
+                setEvaluatable(n);
+            }
             join = join.getJoin();
         } while (join != null);
     }
@@ -181,6 +207,11 @@ public class TableFilter implements ColumnResolver {
      */
     public void setPlanItem(PlanItem item) {
         setIndex(item.getIndex());
+        if (nestedJoin != null) {
+            if (item.getNestedJoinPlan() != null) {
+                nestedJoin.setPlanItem(item.getNestedJoinPlan());
+            }
+        }
         if (join != null) {
             if (item.getJoinPlan() != null) {
                 join.setPlanItem(item.getJoinPlan());
@@ -204,6 +235,12 @@ public class TableFilter implements ColumnResolver {
                 }
             }
         }
+        if (nestedJoin != null) {
+            if (SysProperties.CHECK && nestedJoin == this) {
+                DbException.throwInternalError("self join");
+            }
+            nestedJoin.prepare();
+        }
         if (join != null) {
             if (SysProperties.CHECK && join == this) {
                 DbException.throwInternalError("self join");
@@ -226,6 +263,9 @@ public class TableFilter implements ColumnResolver {
     public void startQuery(Session s) {
         this.session = s;
         scanCount = 0;
+        if (nestedJoin != null) {
+            nestedJoin.startQuery(s);
+        }
         if (join != null) {
             join.startQuery(s);
         }
@@ -235,6 +275,9 @@ public class TableFilter implements ColumnResolver {
      * Reset to the current position.
      */
     public void reset() {
+        if (nestedJoin != null) {
+            nestedJoin.reset();
+        }
         if (join != null) {
             join.reset();
         }
@@ -253,17 +296,37 @@ public class TableFilter implements ColumnResolver {
         } else if (state == BEFORE_FIRST) {
             cursor.find(session, indexConditions);
             if (!cursor.isAlwaysFalse()) {
+                if (nestedJoin != null) {
+                    nestedJoin.reset();
+                }
                 if (join != null) {
                     join.reset();
                 }
             }
         } else {
-            // state == FOUND || LAST_ROW
+            // state == FOUND || NULL_ROW
             // the last row was ok - try next row of the join
+            if (nestedJoin != null) {
+                if (join == null) {
+                    if (nestedJoin.next()) {
+                        return true;
+                    }
+                } else {
+                    while (true) {
+                        if (nestedJoin.next()) {
+                            if (join.next()) {
+                                return true;
+                            }
+                            join.reset();
+                        }
+                    }
+                }
+            } else {
                 if (join != null && join.next()) {
                     return true;
                 }
             }
+        }
         while (true) {
             // go to the next row
             if (state == NULL_ROW) {
@@ -285,14 +348,18 @@ public class TableFilter implements ColumnResolver {
             }
             // if no more rows found, try the null row (for outer joins only)
             if (state == AFTER_LAST) {
-                if (outerJoin && !foundOne) {
-                    state = NULL_ROW;
-                    current = table.getNullRow();
-                    currentSearchRow = current;
+                if (joinOuter && !foundOne) {
+                    setNullRow();
                 } else {
                     break;
                 }
             }
+            if (state == FOUND && nestedJoin != null) {
+                nestedJoin.reset();
+                if (!nestedJoin.next()) {
+                    continue;
+                }
+            }
             if (!isOk(filterCondition)) {
                 continue;
             }
@@ -319,6 +386,16 @@ public class TableFilter implements ColumnResolver {
         return false;
     }
     
+    private void setNullRow() {
+        state = NULL_ROW;
+        current = table.getNullRow();
+        currentSearchRow = current;
+        if (nestedJoin != null) {
+            int todoRecurse;
+            nestedJoin.setNullRow();
+        }
+    }
+
     private void checkTimeout() {
         session.checkCanceled();
         // System.out.println(this.alias+ " " + table.getName() + ": " +
@@ -407,26 +484,39 @@ public class TableFilter implements ColumnResolver {
      * @param outer if this is an outer join
      * @param on the join condition
      */
-    public void addJoin(TableFilter filter, boolean outer, Expression on) {
+    public void addJoin(TableFilter filter, boolean outer, boolean nested, Expression on) {
         if (on != null) {
             on.mapColumns(this, 0);
         }
+        if (nested && SysProperties.NESTED_JOINS) {
+            if (nestedJoin != null) {
+                throw DbException.throwInternalError();
+            }
+            nestedJoin = filter;
+            filter.joinOuter = outer;
+            if (on != null) {
+                filter.mapAndAddFilter(on);
+            }
+        } else {
             if (join == null) {
-            this.join = filter;
-            filter.outerJoin = outer;
+                join = filter;
+                filter.joinOuter = outer;
+                if (!SysProperties.NESTED_JOINS) {
                     if (outer) {
                         // convert all inner joins on the right hand side to outer joins
                         TableFilter f = filter.join;
                         while (f != null) {
-                    f.outerJoin = true;
+                            f.joinOuter = true;
                             f = f.join;
                         }
                     }
+                }
                 if (on != null) {
                     filter.mapAndAddFilter(on);
                 }
             } else {
-            join.addJoin(filter, outer, on);
+                join.addJoin(filter, outer, nested, on);
+            }
         }
     }
 
@@ -439,6 +529,9 @@ public class TableFilter implements ColumnResolver {
         on.mapColumns(this, 0);
         addFilterCondition(on, true);
         on.createIndexConditions(session, this);
+        if (nestedJoin != null) {
+            nestedJoin.mapAndAddFilter(on);
+        }
         if (join != null) {
             join.mapAndAddFilter(on);
         }
@@ -454,7 +547,7 @@ public class TableFilter implements ColumnResolver {
      * @return true if it is
      */
     public boolean isJoinOuter() {
-        return outerJoin;
+        return joinOuter;
     }
 
     /**
@@ -466,12 +559,15 @@ public class TableFilter implements ColumnResolver {
     public String getPlanSQL(boolean isJoin) {
         StringBuilder buff = new StringBuilder();
         if (isJoin) {
-            if (outerJoin) {
+            if (joinOuter) {
                 buff.append("LEFT OUTER JOIN ");
             } else {
                 buff.append("INNER JOIN ");
             }
         }
+        if (nestedJoin != null) {
+            buff.append("(");
+        }
         buff.append(table.getSQL());
         if (alias != null) {
             buff.append(' ').append(Parser.quoteIdentifier(alias));
@@ -490,6 +586,11 @@ public class TableFilter implements ColumnResolver {
             String plan = StringUtils.quoteRemarkSQL(planBuff.toString());
             buff.append(plan).append(" */");
         }
+        if (nestedJoin != null) {
+            buff.append('\n');
+            buff.append(nestedJoin.getPlanSQL(true));
+            buff.append(")");
+        }
         if (isJoin) {
             buff.append(" ON ");
             if (joinCondition == null) {
@@ -594,9 +695,12 @@ public class TableFilter implements ColumnResolver {
      */
     void optimizeFullCondition(boolean fromOuterJoin) {
         if (fullCondition != null) {
-            fullCondition.addFilterConditions(this, fromOuterJoin || outerJoin);
+            fullCondition.addFilterConditions(this, fromOuterJoin || joinOuter);
+            if (nestedJoin != null) {
+                nestedJoin.optimizeFullCondition(fromOuterJoin || joinOuter);
+            }
             if (join != null) {
-                join.optimizeFullCondition(fromOuterJoin || outerJoin);
+                join.optimizeFullCondition(fromOuterJoin || joinOuter);
             }
         }
     }
@@ -615,6 +719,9 @@ public class TableFilter implements ColumnResolver {
         if (joinCondition != null) {
             joinCondition.setEvaluatable(filter, b);
         }
+        if (nestedJoin != null) {
+            nestedJoin.setEvaluatable(filter, b);
+        }
         if (join != null) {
             join.setEvaluatable(filter, b);
         }
@@ -744,4 +851,8 @@ public class TableFilter implements ColumnResolver {
         }
     }
 
+    public TableFilter getNestedJoin() {
+        return nestedJoin;
+    }
+
 }

h2/src/test/org/h2/test/TestAll.java

@@ -38,6 +38,7 @@ import org.h2.test.db.TestMultiConn;
 import org.h2.test.db.TestMultiDimension;
 import org.h2.test.db.TestMultiThread;
 import org.h2.test.db.TestMultiThreadedKernel;
+import org.h2.test.db.TestNestedJoins;
 import org.h2.test.db.TestOpenClose;
 import org.h2.test.db.TestOptimizations;
 import org.h2.test.db.TestOutOfMemory;
@@ -302,6 +303,7 @@ java org.h2.test.TestAll timer
         // System.setProperty("h2.largeTransactions", "true");
         // System.setProperty("h2.lobInDatabase", "true");
         // System.setProperty("h2.analyzeAuto", "100");
+        // System.setProperty("h2.nestedJoins", "true");
 
         int speedup;
         // System.setProperty("h2.syncMethod", "");
@@ -516,6 +518,7 @@ kill -9 `jps -l | grep "org.h2.test." | cut -d " " -f 1`
         new TestMultiDimension().runTest(this);
         new TestMultiThread().runTest(this);
         new TestMultiThreadedKernel().runTest(this);
+        new TestNestedJoins().runTest(this);
         new TestOpenClose().runTest(this);
         new TestOptimizations().runTest(this);
         new TestOutOfMemory().runTest(this);

h2/src/test/org/h2/test/db/TestNestedJoins.java

+/*
+ * Copyright 2004-2010 H2 Group. Multiple-Licensed under the H2 License,
+ * Version 1.0, and under the Eclipse Public License, Version 1.0
+ * (http://h2database.com/html/license.html).
+ * Initial Developer: H2 Group
+ */
+package org.h2.test.db;
+
+import java.io.StringReader;
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import org.h2.constant.SysProperties;
+import org.h2.test.TestBase;
+import org.h2.util.ScriptReader;
+
+/**
+ * Tests nested joins and right outer joins.
+ */
+public class TestNestedJoins extends TestBase {
+    
+    /**
+     * Run just this test.
+     *
+     * @param a ignored
+     */
+    public static void main(String... a) throws Exception {
+        System.setProperty("h2.nestedJoins", "true");
+        TestBase.createCaller().init().test();
+    }
+
+    public void test() throws Exception {
+        if (!SysProperties.NESTED_JOINS) {
+            return;
+        }
+        
+        deleteDb("nestedJoins");
+        
+        Connection conn = getConnection("nestedJoins");
+        Statement stat = conn.createStatement();
+        ResultSet rs;
+        String sql;
+        
+        // not yet supported:
+        /*
+        stat.execute("drop table a, b, c");
+        stat.execute("create table a(x int)");
+        stat.execute("create table b(x int)");
+        stat.execute("create table c(x int, y int)");
+        stat.execute("insert into a values(1), (2)");
+        stat.execute("insert into b values(3)");
+        stat.execute("insert into c values(1, 3)");
+        stat.execute("insert into c values(4, 5)");
+        rs = stat.executeQuery("explain select * from a left outer join (b left outer join c on b.x = c.y) on a.x = c.x");
+        assertTrue(rs.next());
+        sql = cleanRemarks(conn, rs.getString(1));
+        assertEquals("", sql);
+
+        rs = stat.executeQuery("select * from a left outer join (b left outer join c on b.x = c.y) on a.x = c.x");
+        // expected result: 1   3       1       3;  2       null    null    null
+        assertTrue(rs.next());
+        assertEquals("1", rs.getString(1));
+        assertEquals("3", rs.getString(2));
+        assertEquals("1", rs.getString(3));
+        assertEquals("3", rs.getString(4));
+        assertTrue(rs.next());
+        assertEquals("2", rs.getString(1));
+        assertEquals(null, rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertEquals(null, rs.getString(4));
+        assertFalse(rs.next());
+        */
+
+        stat.execute("create table a(x int primary key)");
+        stat.execute("insert into a values(0), (1)");
+        stat.execute("create table b(x int primary key)");
+        stat.execute("insert into b values(0)");
+        stat.execute("create table c(x int primary key)");
+
+        rs = stat.executeQuery("select a.*, b.*, c.* from a left outer join (b inner join c on b.x = c.x) on a.x = b.x");
+        // expected result: 0, null, null; 1, null, null
+        assertTrue(rs.next());
+        assertEquals("0", rs.getString(1));
+        assertEquals(null, rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertTrue(rs.next());
+        assertEquals("1", rs.getString(1));
+        assertEquals(null, rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertFalse(rs.next());
+        
+        rs = stat.executeQuery("select * from a left outer join b on a.x = b.x inner join c on b.x = c.x");
+        // expected result: -
+        assertFalse(rs.next());
+
+        rs = stat.executeQuery("select * from a left outer join b on a.x = b.x left outer join c on b.x = c.x");
+        // expected result: 0   0       null; 1       null    null
+        assertTrue(rs.next());
+        assertEquals("0", rs.getString(1));
+        assertEquals("0", rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertTrue(rs.next());
+        assertEquals("1", rs.getString(1));
+        assertEquals(null, rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertFalse(rs.next());
+        
+        rs = stat.executeQuery("select * from a left outer join (b inner join c on b.x = c.x) on a.x = b.x");
+        // expected result: 0   null    null; 1       null    null
+        assertTrue(rs.next());
+        assertEquals("0", rs.getString(1));
+        assertEquals(null, rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertTrue(rs.next());
+        assertEquals("1", rs.getString(1));
+        assertEquals(null, rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertFalse(rs.next());
+        
+        rs = stat.executeQuery("explain select * from a left outer join (b inner join c on c.x = 1) on a.x = b.x");
+        assertTrue(rs.next());
+        sql = cleanRemarks(conn, rs.getString(1));
+        assertEquals("SELECT A.X, B.X, C.X FROM PUBLIC.A LEFT OUTER JOIN (PUBLIC.B INNER JOIN PUBLIC.C ON (C.X = 1) AND (A.X = B.X)) ON A.X = B.X", sql);
+
+        stat.execute("create table test(id int primary key)");
+        stat.execute("insert into test values(0), (1), (2)");
+        rs = stat.executeQuery("select * from test a left outer join (test b inner join test c on b.id = c.id - 2) on a.id = b.id + 1");
+        // drop table test;
+        // create table test(id int primary key);
+        // insert into test values(0), (1), (2);
+        // select * from test a left outer join (test b inner join test c on b.id = c.id - 2) on a.id = b.id + 1;
+        // expected result: 0   null    null; 1       0       2; 2       null    null
+        assertTrue(rs.next());
+        assertEquals("0", rs.getString(1));
+        assertEquals(null, rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertTrue(rs.next());
+        assertEquals("1", rs.getString(1));
+        assertEquals("0", rs.getString(2));
+        assertEquals("2", rs.getString(3));
+        assertTrue(rs.next());
+        assertEquals("2", rs.getString(1));
+        assertEquals(null, rs.getString(2));
+        assertEquals(null, rs.getString(3));
+        assertFalse(rs.next());
+        
+        // while (rs.next()) {
+        //     for (int i = 0; i < rs.getMetaData().getColumnCount(); i++) {
+        //         System.out.print(rs.getString(i + 1) + " ");
+        //     }
+        //     System.out.println();
+        // }
+        
+        conn.close();
+        deleteDb("nestedJoins");
+    }
+
+    private String cleanRemarks(Connection conn, String sql) throws SQLException {
+        ScriptReader r = new ScriptReader(new StringReader(sql));
+        r.setSkipRemarks(true);
+        sql = r.readStatement();
+        sql = sql.replaceAll("\\n", " ");
+        // sql = sql.replaceAll("\\/\\*.*\\*\\/", "");
+        while (sql.indexOf("  ") >= 0) {
+            sql = sql.replaceAll("  ", " ");
+        }
+        return sql;
+    }
+}

h2/src/test/org/h2/test/todo/todo.txt

@@ -2,23 +2,6 @@ Nested Outer Joins
 -----------------
 Example:
 
-drop table a, b, c;
-create table a(x int primary key);
-insert into a values(0), (1);
-create table b(x int primary key);
-insert into b values(0);
-create table c(x int primary key);
-select * from a left outer join b on a.x = b.x inner join c on b.x = c.x;
-select * from a left outer join b on a.x = b.x left outer join c on b.x = c.x;
-select * from a left outer join (b inner join c on b.x = c.x) on a.x = b.x;
-select a.x, b_x, c_x from a left outer join (select b.x b_x, c.x c_x from b inner join c on b.x = c.x) on a.x = b_x;
-
-drop table test;
-create table test(id int primary key);
-insert into test values(0), (1), (2);
-select * from test a left outer join (test b inner join test c on b.id = c.id - 2) on a.id = b.id + 1;
-select a.id, b_id, c_id from test a left outer join (select b.id b_id, c.id c_id from test b inner join test c on b.id = c.id - 2) on a.id = b_id + 1;
-
 create table a(x int);
 create table b(x int);
 create table c(x int, y int);