private void checkNullable() {
for (Index index : table.getIndexes()) {
if (index.getColumnIndex(oldColumn) < 0) {
continue;
}
IndexType indexType = index.getIndexType();
if (indexType.isPrimaryKey() || indexType.isHash()) {
throw DbException.get(ErrorCode.COLUMN_IS_PART_OF_INDEX_1, index.getSQL());
}
}
}
public MergedResult(List<Result> results, Select newSelect, Select oldSelect) {
// 1. 结果集串行化，为合并做准备
SerializedResult serializedResult = new SerializedResult(results, oldSelect.getLimitRows());
Table table = newSelect.getTopTableFilter().getTable();
newSelect
.getTopTableFilter()
.setIndex(
new MergedIndex(
serializedResult,
table,
-1,
IndexColumn.wrap(table.getColumns()),
IndexType.createScan(false)));
// 2. 把多个结果集合并
Result mergedResult = newSelect.queryGroupMerge();
// 3. 计算合并后的结果集,
// 例如oldSelect="select avg"时，在分布式环境要转成newSelect="select count, sum"，
// 此时就由count, sum来算出avg
Result calculatedResult = oldSelect.calculate(mergedResult, newSelect);
// 4. 如果不存在avg、stddev这类需要拆分为count、sum的计算，
// 此时mergedResult和calculatedResult是同一个实例，否则就是不同实例
if (mergedResult != calculatedResult) {
mergedResult.close();
result = calculatedResult;
} else {
result = mergedResult;
}
}