241 lines
9.5 KiB
C++
241 lines
9.5 KiB
C++
/**
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* Copyright (c) 2021 OceanBase
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* OceanBase CE is licensed under Mulan PubL v2.
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* You can use this software according to the terms and conditions of the Mulan PubL v2.
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* You may obtain a copy of Mulan PubL v2 at:
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* http://license.coscl.org.cn/MulanPubL-2.0
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* THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
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* EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
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* MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
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* See the Mulan PubL v2 for more details.
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*/
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#define USING_LOG_PREFIX SQL_REWRITE
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#include "sql/rewrite/ob_transform_simplify_distinct.h"
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#include "sql/optimizer/ob_optimizer_util.h"
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#include "sql/rewrite/ob_transform_utils.h"
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#include "common/ob_smart_call.h"
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using namespace oceanbase::sql;
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int ObTransformSimplifyDistinct::transform_one_stmt(common::ObIArray<ObParentDMLStmt> &parent_stmts,
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ObDMLStmt *&stmt,
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bool &trans_happened)
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{
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int ret = OB_SUCCESS;
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bool is_const_distinct = false;
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bool is_unique_distinct = false;
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ObSelectStmt *sel_stmt = static_cast<ObSelectStmt *>(stmt);
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UNUSED(parent_stmts);
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if (OB_ISNULL(stmt)) {
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ret = OB_ERR_UNEXPECTED;
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LOG_WARN("stmt is null", K(ret));
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} else if (!stmt->is_select_stmt()) {
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// do nothing
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OPT_TRACE("not select stmt");
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} else if (OB_FAIL(remove_distinct_on_const_exprs(sel_stmt, is_const_distinct))) {
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LOG_WARN("failed to remove distinct for const exprs", K(ret));
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} else if (OB_FAIL(remove_distinct_on_unique_exprs(sel_stmt, is_unique_distinct))) {
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LOG_WARN("failed to remove distinct for unique exprs", K(ret));
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} else {
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trans_happened = is_const_distinct || is_unique_distinct;
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}
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if (OB_SUCC(ret) && trans_happened) {
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if (OB_FAIL(add_transform_hint(*stmt))) {
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LOG_WARN("failed to add transform hint", K(ret));
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}
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}
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return ret;
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}
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int ObTransformSimplifyDistinct::remove_distinct_on_const_exprs(ObSelectStmt *stmt, bool &trans_happened)
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{
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int ret = OB_SUCCESS;
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bool is_valid = false;
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trans_happened = false;
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ObConstRawExpr *limit_count_expr = NULL;
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OPT_TRACE("try to remove distinct on const exprs");
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if (OB_ISNULL(stmt) || OB_ISNULL(ctx_) || OB_ISNULL(ctx_->expr_factory_)) {
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ret = OB_ERR_UNEXPECTED;
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LOG_WARN("stmt is unexpected null", K(ret), K(stmt), K(ctx_));
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} else if (OB_FAIL(distinct_can_be_eliminated(stmt, is_valid))) {
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LOG_WARN("distinct_can_be_eliminated() fails unexpectedly", K(ret));
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} else if (!is_valid) {
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// do nothing
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OPT_TRACE("can not eliminate");
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} else if (OB_FAIL(ObRawExprUtils::build_const_int_expr(*ctx_->expr_factory_,
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ObIntType,
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1L,
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limit_count_expr))) {
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LOG_WARN("Failed to create expr", K(ret));
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} else if (OB_ISNULL(limit_count_expr)) {
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ret = OB_ERR_UNEXPECTED;
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LOG_WARN("limit_count_expr is null", K(ret));
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} else if (OB_FAIL(limit_count_expr->formalize(ctx_->session_info_))) {
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LOG_WARN("failed to formalize a new expr", K(ret));
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} else {
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// Eliminate DISTINCT and create a `LIMIT 1`
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stmt->set_limit_offset(limit_count_expr, NULL);
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stmt->assign_all();
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trans_happened = true;
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}
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return ret;
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}
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int ObTransformSimplifyDistinct::distinct_can_be_eliminated(ObSelectStmt *stmt, bool &can_be)
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{
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int ret = OB_SUCCESS;
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can_be = false;
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if (OB_ISNULL(stmt) || OB_ISNULL(ctx_)) {
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ret = OB_ERR_UNEXPECTED;
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LOG_WARN("get unexpected null", K(ret), K(stmt), K(ctx_));
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} else if (stmt->is_contains_assignment() ||
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stmt->is_calc_found_rows()) {
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// Do nothing for non-select query.
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// When there are `@var := ` assignment, don't eliminate distinct.
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OPT_TRACE("stmt has assignment or calc found rows");
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} else if (stmt->has_distinct() && !stmt->is_set_stmt() && stmt->get_from_item_size() > 0 &&
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!stmt->has_rollup()) {
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// Only try to eliminate DISTINCT for plain SELECT
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int64_t limit_count = 0;
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const ObConstRawExpr *limit_expr = static_cast<ObConstRawExpr *>(stmt->get_limit_expr());
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const ObRawExpr *limit_offset_expr = stmt->get_offset_expr();
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if (limit_expr != NULL) {
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limit_count = limit_expr->get_value().get_int();
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}
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if (!stmt->has_limit() ||
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(limit_offset_expr == NULL && limit_count > 0)) {
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bool contain_only = true;
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EqualSets &equal_sets = ctx_->equal_sets_;
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ObArenaAllocator alloc;
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ObSEArray<ObRawExpr *, 4> const_exprs;
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const ObIArray<ObRawExpr *> &conditions = stmt->get_condition_exprs();
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if (OB_FAIL(stmt->get_stmt_equal_sets(equal_sets, alloc, true, true))) {
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LOG_WARN("failed to get stmt equal sets", K(ret));
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} else if (OB_FAIL(ObOptimizerUtil::compute_const_exprs(conditions, const_exprs))) {
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LOG_WARN("failed to compute const equivalent exprs", K(ret));
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}
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for (int64_t i = 0; OB_SUCC(ret) && contain_only && i < stmt->get_select_item_size(); ++i) {
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ObRawExpr *expr = stmt->get_select_item(i).expr_;
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bool is_const = false;
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if (OB_FAIL(ObOptimizerUtil::is_const_expr(expr, equal_sets, const_exprs, is_const))) {
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LOG_WARN("check expr whether const expr failed", K(ret));
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} else {
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contain_only = is_const;
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}
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}
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equal_sets.reuse();
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if (OB_SUCC(ret) && contain_only) {
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can_be = true;
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} else { /* Do nothing */ }
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} else { /* Do nothing */ }
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} else { /* Do nothing */ }
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return ret;
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}
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int ObTransformSimplifyDistinct::remove_distinct_on_unique_exprs(ObSelectStmt *stmt, bool &trans_happened)
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{
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int ret = OB_SUCCESS;
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bool is_unique = false;
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ObSEArray<ObRawExpr *, 16> select_exprs;
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OPT_TRACE("try to remove distinct on unique exprs");
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if (OB_ISNULL(stmt) || OB_ISNULL(ctx_)) {
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ret = OB_ERR_UNEXPECTED;
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LOG_WARN("get unexpected null", K(ret), K(stmt), K(ctx_));
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} else if (!stmt->has_distinct()) {
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// do nothing
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OPT_TRACE("stmt do not has distinct");
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} else if (OB_FAIL(stmt->get_select_exprs(select_exprs))) {
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LOG_WARN("failed to get select exprs", K(ret));
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} else if (OB_FAIL(ObTransformUtils::check_stmt_unique(stmt, ctx_->session_info_,
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ctx_->schema_checker_,
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select_exprs,
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true /* strict */,
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is_unique, true))) {
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LOG_WARN("failed to check stmt unique", K(ret));
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} else if (is_unique) {
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stmt->assign_all();
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trans_happened = true;
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} else {
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OPT_TRACE("select expr is not unique, can not eliminate");
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}
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if (OB_SUCC(ret) && stmt->is_set_stmt()) {
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OPT_TRACE("try to remove child stmt`s distinct for set stmt");
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if (OB_FAIL(remove_child_stmt_distinct(stmt, trans_happened))) {
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LOG_WARN("failed to remove child stmt distinct", K(ret));
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}
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}
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return ret;
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}
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//消除distinct set op left/right query中的distinct
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int ObTransformSimplifyDistinct::remove_child_stmt_distinct(ObSelectStmt *set_stmt,
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bool &trans_happened)
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{
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int ret = OB_SUCCESS;
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trans_happened = false;
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if (OB_ISNULL(set_stmt) || !set_stmt->is_set_stmt()) {
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ret = OB_ERR_UNEXPECTED;
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LOG_WARN("unexpected stmt", K(ret));
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} else if (!set_stmt->is_set_distinct() ||
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ObSelectStmt::RECURSIVE == set_stmt->get_set_op()) {
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/*do nothing*/
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OPT_TRACE("union all or recurisve union can not remove distinct");
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} else {
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bool child_happended = false;
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ObIArray<ObSelectStmt*> &child_stmts = set_stmt->get_set_query();
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for (int64_t i = 0; OB_SUCC(ret) && i < child_stmts.count(); ++i) {
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if (OB_FAIL(try_remove_child_stmt_distinct(child_stmts.at(i), child_happended))) {
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LOG_WARN("failed to try remove child stmt distinct", K(ret));
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} else {
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trans_happened |= child_happended;
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}
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}
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}
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return ret;
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}
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//递归消除disticnt条件：
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// 1.stmt 为非 recursive 的 set op, 无 limit, 尝试向下递归删除
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// 2.stmt 非 set, 无 sequence/limit/rownum, 可消除distinct
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int ObTransformSimplifyDistinct::try_remove_child_stmt_distinct(ObSelectStmt *stmt,
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bool &trans_happened)
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{
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int ret = OB_SUCCESS;
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trans_happened = false;
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if (OB_ISNULL(stmt)) {
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ret = OB_ERR_UNEXPECTED;
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LOG_WARN("unexpected null", K(ret), K(stmt));
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} else if (!stmt->is_set_stmt()) {
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bool has_rownum = false;
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if (!stmt->has_distinct()
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|| stmt->has_sequence()
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|| stmt->has_limit()) {
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/*do nothing*/
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OPT_TRACE("stmt do not has distinct or has sequence/limit");
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} else if (OB_FAIL(stmt->has_rownum(has_rownum))) {
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LOG_WARN("failed to check has rownum", K(ret));
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} else if (!has_rownum) {
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stmt->assign_all();
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trans_happened = true;
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} else {
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OPT_TRACE("stmt has rownum");
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}
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} else if (ObSelectStmt::RECURSIVE == stmt->get_set_op() || stmt->has_limit()) {
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/*do nothing*/
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OPT_TRACE("is recursive union or stmt has limit");
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} else {
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bool child_happended = false;
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ObIArray<ObSelectStmt*> &child_stmts = stmt->get_set_query();
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for (int64_t i = 0; OB_SUCC(ret) && i < child_stmts.count(); ++i) {
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if (OB_FAIL(SMART_CALL(try_remove_child_stmt_distinct(child_stmts.at(i), child_happended)))) {
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LOG_WARN("failed to try remove child stmt distinct", K(ret));
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} else {
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trans_happened |= child_happended;
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}
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}
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}
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return ret;
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}
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