Implement derived column list syntax on table alias

h2/src/docsrc/help/help.csv

@@ -2256,7 +2256,8 @@ ID + 20
 "
 
 "Other Grammar","Table Expression","
-{ [ schemaName. ] tableName | ( select ) | valuesExpression } [ [ AS ] newTableAlias ]
+{ [ schemaName. ] tableName | ( select ) | valuesExpression }
+[ [ AS ] newTableAlias [ ( columnName [,...] ) ] ]
 [ USE INDEX ([ indexName [,...] ]) ]
 [ { { LEFT | RIGHT } [ OUTER ] | [ INNER ] | CROSS | NATURAL }
     JOIN tableExpression [ ON expression ] ]

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

@@ -1374,6 +1374,14 @@ public class Parser {
                 alias = readFromAlias(null);
                 if (alias != null) {
                     top.setAlias(alias);
+                    if (readIf("(")) {
+                        ArrayList<String> derivedColumnNames = New.arrayList();
+                        do {
+                            derivedColumnNames.add(readAliasIdentifier());
+                        } while (readIf(","));
+                        read(")");
+                        top.setDerivedColumns(derivedColumnNames);
+                    }
                 }
                 return top;
             }

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

@@ -737,8 +737,9 @@ public class Select extends Query {
             if (filter.isNaturalJoinColumn(c)) {
                 continue;
             }
+            String name = filter.getDerivedColumnName(c);
             ExpressionColumn ec = new ExpressionColumn(
-                    session.getDatabase(), null, alias, c.getName());
+                    session.getDatabase(), null, alias, name != null ? name : c.getName());
             expressions.add(index++, ec);
         }
         return index;

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

@@ -52,6 +52,11 @@ public class SelectListColumnResolver implements ColumnResolver {
         return columns;
     }
 
+    @Override
+    public String getDerivedColumnName(Column column) {
+        return null;
+    }
+
     @Override
     public String getSchemaName() {
         return null;

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

@@ -33,7 +33,7 @@ public class ExpressionColumn extends Expression {
     private final Database database;
     private final String schemaName;
     private final String tableAlias;
-    private final String columnName;
+    private String columnName;
     private ColumnResolver columnResolver;
     private int queryLevel;
     private Column column;
@@ -89,7 +89,10 @@ public class ExpressionColumn extends Expression {
             return;
         }
         for (Column col : resolver.getColumns()) {
-            String n = col.getName();
+            String n = resolver.getDerivedColumnName(col);
+            if (n == null) {
+                n = col.getName();
+            }
             if (database.equalsIdentifiers(columnName, n)) {
                 mapColumn(resolver, col, level);
                 return;
@@ -253,6 +256,12 @@ public class ExpressionColumn extends Expression {
     @Override
     public String getAlias() {
         if (column != null) {
+            if (columnResolver != null) {
+                String name = columnResolver.getDerivedColumnName(column);
+                if (name != null) {
+                    return name;
+                }
+            }
             return column.getName();
         }
         if (tableAlias != null) {

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

@@ -30,6 +30,14 @@ public interface ColumnResolver {
      */
     Column[] getColumns();
 
+    /**
+     * Get derived column name, or {@code null}.
+     *
+     * @param column column
+     * @return derived column name, or {@code null}
+     */
+    String getDerivedColumnName(Column column);
+
     /**
      * Get the list of system columns, if any.
      *

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

@@ -42,6 +42,11 @@ public class SingleColumnResolver implements ColumnResolver {
         return new Column[] { column };
     }
 
+    @Override
+    public String getDerivedColumnName(Column column) {
+        return null;
+    }
+
     @Override
     public String getSchemaName() {
         return null;

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

@@ -6,6 +6,7 @@
 package org.h2.table;
 
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.HashSet;
 import org.h2.api.ErrorCode;
 import org.h2.command.Parser;
@@ -117,6 +118,8 @@ public class TableFilter implements ColumnResolver {
     private final int hashCode;
     private final int orderInFrom;
 
+    private HashMap<Column, String> derivedColumnMap;
+
     /**
      * Create a new table filter object.
      *
@@ -992,6 +995,12 @@ public class TableFilter implements ColumnResolver {
         return table.getColumns();
     }
 
+    @Override
+    public String getDerivedColumnName(Column column) {
+        HashMap<Column, String> map = derivedColumnMap;
+        return map != null ? map.get(column) : null;
+    }
+
     /**
      * Get the system columns that this table understands. This is used for
      * compatibility with other databases. The columns are only returned if the
@@ -1056,6 +1065,30 @@ public class TableFilter implements ColumnResolver {
         this.alias = alias;
     }
 
+    /**
+     * Set derived column list.
+     *
+     * @param derivedColumnNames names of derived columns
+     */
+    public void setDerivedColumns(ArrayList<String> derivedColumnNames) {
+        Column[] columns = getColumns();
+        int count = columns.length;
+        if (count != derivedColumnNames.size()) {
+            throw DbException.get(ErrorCode.COLUMN_COUNT_DOES_NOT_MATCH);
+        }
+        HashMap<Column, String> map = new HashMap<>(count);
+        for (int i = 0; i < count; i++) {
+            String alias = derivedColumnNames.get(i);
+            for (int j = 0; j < i; j++) {
+                if (alias.equals(derivedColumnNames.get(j))) {
+                    throw DbException.get(ErrorCode.DUPLICATE_COLUMN_NAME_1, alias);
+                }
+            }
+            map.put(columns[i], alias);
+        }
+        this.derivedColumnMap = map;
+    }
+
     @Override
     public Expression optimize(ExpressionColumn expressionColumn, Column column) {
         return expressionColumn;

h2/src/test/org/h2/test/scripts/TestScript.java

@@ -82,6 +82,7 @@ public class TestScript extends TestBase {
         reconnectOften = !config.memory && config.big;
 
         testScript("testScript.sql");
+        testScript("aliases.sql");
         testScript("joins.sql");
         testScript("altertable-index-reuse.sql");
         testScript("query-optimisations.sql");

h2/src/test/org/h2/test/scripts/aliases.sql

+-- Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
+-- and the EPL 1.0 (http://h2database.com/html/license.html).
+-- Initial Developer: H2 Group
+--
+
+SELECT * FROM (VALUES(1, 2));
+> C1 C2
+> -- --
+> 1  2
+> rows: 1
+
+SELECT * FROM (VALUES(1, 2)) AS T;
+> C1 C2
+> -- --
+> 1  2
+> rows: 1
+
+SELECT * FROM (VALUES(1, 2)) AS T(A, B);
+> A B
+> - -
+> 1 2
+> rows: 1
+
+SELECT A AS A1, B AS B1 FROM (VALUES(1, 2)) AS T(A, B);
+> A1 B1
+> -- --
+> 1  2
+> rows: 1
+
+SELECT A AS A1, B AS B1 FROM (VALUES(1, 2)) AS T(A, B) WHERE A <> B;
+> A1 B1
+> -- --
+> 1  2
+> rows: 1
+
+SELECT A AS A1, B AS B1 FROM (VALUES(1, 2)) AS T(A, B) WHERE A1 <> B1;
+> exception
+
+SELECT * FROM (VALUES(1, 2)) AS T(A);
+> exception
+
+SELECT * FROM (VALUES(1, 2)) AS T(A, a);
+> exception
+
+SELECT * FROM (VALUES(1, 2)) AS T(A, B, C);
+> exception
+
+SELECT V AS V1, A AS A1, B AS B1 FROM (VALUES (1)) T1(V) INNER JOIN (VALUES(1, 2)) T2(A, B) ON V = A;
+> V1 A1 B1
+> -- -- --
+> 1  1  2
+> rows: 1