Make implementation, description, and examples for ALTER TABLE DROP COLUMN consistent

h2/src/docsrc/help/help.csv

@@ -373,13 +373,14 @@ ALTER TABLE TEST ALTER COLUMN NAME SET INVISIBLE;
 
 "Commands (DDL)","ALTER TABLE DROP COLUMN","
 ALTER TABLE [ IF EXISTS ] tableName DROP COLUMN [ IF EXISTS ]
-( columnName [,...] )
+columnName [,...] | ( columnName [,...] )
 ","
 Removes column(s) from a table.
 This command commits an open transaction in this connection.
 ","
 ALTER TABLE TEST DROP COLUMN NAME
 ALTER TABLE TEST DROP COLUMN NAME1, NAME2
+ALTER TABLE TEST DROP COLUMN (NAME1, NAME2)
 "
 
 "Commands (DDL)","ALTER TABLE DROP CONSTRAINT","

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

@@ -6103,28 +6103,28 @@ public class Parser {
             } else {
                 readIf("COLUMN");
                 boolean ifExists = readIfExists(false);
-                AlterTableAlterColumn command = new AlterTableAlterColumn(
-                        session, schema);
-                command.setType(CommandInterface.ALTER_TABLE_DROP_COLUMN);
                 ArrayList<Column> columnsToRemove = New.arrayList();
                 Table table = tableIfTableExists(schema, tableName, ifTableExists);
                 // For Oracle compatibility - open bracket required
                 boolean openingBracketDetected = readIf("(");
                 do {
                     String columnName = readColumnIdentifier();
-                    if (table == null) {
-                        return new NoOperation(session);
-                    }
-                    if (ifExists && !table.doesColumnExist(columnName)) {
-                        return new NoOperation(session);
+                    if (table != null) {
+                        if (!ifExists || table.doesColumnExist(columnName)) {
+                            Column column = table.getColumn(columnName);
+                            columnsToRemove.add(column);
+                        }
                     }
-                    Column column = table.getColumn(columnName);
-                    columnsToRemove.add(column);
                 } while (readIf(","));
                 if (openingBracketDetected) {
                     // For Oracle compatibility - close bracket
                     read(")");
                 }
+                if (table == null || columnsToRemove.isEmpty()) {
+                    return new NoOperation(session);
+                }
+                AlterTableAlterColumn command = new AlterTableAlterColumn(session, schema);
+                command.setType(CommandInterface.ALTER_TABLE_DROP_COLUMN);
                 command.setTableName(tableName);
                 command.setIfTableExists(ifTableExists);
                 command.setColumnsToRemove(columnsToRemove);

h2/src/test/org/h2/test/scripts/ddl/alterTableDropColumn.sql

@@ -11,3 +11,70 @@ ALTER TABLE TEST DROP COLUMN B;
 
 DROP TABLE TEST;
 > ok
+
+ALTER TABLE IF EXISTS TEST DROP COLUMN A;
+> ok
+
+ALTER TABLE TEST DROP COLUMN A;
+> exception
+
+CREATE TABLE TEST(A INT, B INT, C INT, D INT, E INT, F INT, G INT, H INT, I INT, J INT);
+> ok
+
+ALTER TABLE TEST DROP COLUMN IF EXISTS J;
+> ok
+
+ALTER TABLE TEST DROP COLUMN J;
+> exception
+
+ALTER TABLE TEST DROP COLUMN B;
+> ok
+
+ALTER TABLE TEST DROP COLUMN IF EXISTS C;
+> ok
+
+SELECT * FROM TEST;
+> A D E F G H I
+> - - - - - - -
+> rows: 0
+
+ALTER TABLE TEST DROP COLUMN B, D;
+> exception
+
+ALTER TABLE TEST DROP COLUMN IF EXISTS B, D;
+> ok
+
+SELECT * FROM TEST;
+> A E F G H I
+> - - - - - -
+> rows: 0
+
+ALTER TABLE TEST DROP COLUMN E, F;
+> ok
+
+SELECT * FROM TEST;
+> A G H I
+> - - - -
+> rows: 0
+
+ALTER TABLE TEST DROP COLUMN (B, H);
+> exception
+
+ALTER TABLE TEST DROP COLUMN IF EXISTS (B, H);
+> ok
+
+SELECT * FROM TEST;
+> A G I
+> - - -
+> rows: 0
+
+ALTER TABLE TEST DROP COLUMN (G, I);
+> ok
+
+SELECT * FROM TEST;
+> A
+> -
+> rows: 0
+
+DROP TABLE TEST;
+> ok