/**
* This function prepares the from-clause for use by the planner to generate an actual execution
* plan from the clause. This includes several important tasks:
*
* <ul>
* <li>The schema of the from-clause's output is determined.
* <li>If the from-clause is a join, and the join specifies <tt>NATURAL</tt>, <tt>USING (col,
* ...)</tt>, or an <tt>ON</tt> clause, the join condition is determined
* </ul>
*
* <p>Since a from-clause can be a SQL subquery or a join expression, it should be evident that
* the method will recursively prepare its children as well.
*
* <p><b>This method really shouldn't be called directly.</b> Instead, the enclosing {@link
* SelectClause} will calls this method when the clause's {@link SelectClause#computeSchema}
* method is invoked.
*
* @return the schema of the from-clause's output
* @throws IOException if a table's schema cannot be loaded, or some other IO issue occurs.
*/
public Schema prepare() throws IOException {
Schema result = null;
switch (clauseType) {
case BASE_TABLE:
logger.debug("Preparing BASE_TABLE from-clause.");
TableFileInfo tblFileInfo = StorageManager.getInstance().openTable(tableName);
result = tblFileInfo.getSchema();
if (aliasName != null) {
// Make a copy of the result schema and change the table names.
result = new Schema(result);
result.setTableName(aliasName);
}
break;
case SELECT_SUBQUERY:
logger.debug("Preparing SELECT_SUBQUERY from-clause.");
result = derivedTable.computeSchema();
assert aliasName != null;
// Make a copy of the result schema and change the table names.
result = new Schema(result);
result.setTableName(aliasName);
break;
case JOIN_EXPR:
logger.debug("Preparing JOIN_EXPR from-clause. Condition type = " + condType);
result = new Schema();
Schema leftSchema = leftChild.prepare();
Schema rightSchema = rightChild.prepare();
// Depending on the join type, we might eliminate duplicate column
// names.
if (condType == JoinConditionType.NATURAL_JOIN) {
// Make sure that each side of the join doesn't have any
// duplicate column names. (A schema can have columns with the
// same name, but from different table names. This is not
// allowed for natural joins.)
if (leftSchema.hasMultipleColumnsWithSameName()) {
throw new SchemaNameException(
"Natural join error: "
+ "left child table has multiple columns with same "
+ "column name");
}
if (rightSchema.hasMultipleColumnsWithSameName()) {
throw new SchemaNameException(
"Natural join error: "
+ "right child table has multiple columns with same "
+ "column name");
}
Set<String> commonCols = leftSchema.getCommonColumnNames(rightSchema);
if (commonCols.isEmpty()) {
// TODO: According to the SQL99 standard, this shouldn't
// generate an error.
throw new SchemaNameException(
"Natural join error: " + "child tables share no common column names!");
}
buildJoinSchema("Natural join", leftSchema, rightSchema, commonCols, result);
} else if (condType == JoinConditionType.JOIN_USING) {
LinkedHashSet<String> commonCols = new LinkedHashSet<String>();
for (String name : joinUsingNames) {
if (!commonCols.add(name)) {
throw new SchemaNameException(
"Column name " + name + " was specified multiple times in USING clause");
}
}
buildJoinSchema("Join USING", leftSchema, rightSchema, commonCols, result);
} else {
// This join condition-type doesn't alter the result schema.
// Just lump together the result schemas.
result.append(leftSchema);
result.append(rightSchema);
preparedJoinExpr = joinOnExpr;
}
}
// Don't need to do any schema validation in this function, since all the
// validation takes place in the SELECT clause schema-computation code.
preparedSchema = result;
return result;
}
/**
* Initialize the tuple-remover object with the details it needs to delete tuples from the
* specified table.
*
* @param tblFileInfo details of the table that will be modified
*/
public TupleRemover(TableFileInfo tblFileInfo) {
this.tblFileInfo = tblFileInfo;
this.tableMgr = tblFileInfo.getTableManager();
this.eventDispatch = EventDispatcher.getInstance();
}
