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when subquery return empty set result, transformer should not remove select.

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my0
2021-09-17 10:45:38 +08:00
committed by wangzelin.wzl
parent a87cb43159
commit 198966a9ef
1 changed files with 13 additions and 18 deletions
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31
src/sql/rewrite/ob_transform_simplify.cpp
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@ -3006,36 +3006,31 @@ int ObTransformSimplify::try_remove_redundent_select(ObSelectStmt& stmt, ObSelec
} }
return ret; return ret;
} }
/** /**
* @brief check_subquery_valid * @brief check_subquery_valid
* check subquery return equal or less than one row * check subquery return equal one row, if empty do nothing
* has limit 可能使结果为空不做改写;
* select ... where rownum >2; rownum不包含1必空，包含判断较难，暂不处理
* subquery should in format of: * subquery should in format of:
* 1. select ... from dual; * 1. select ... from dual; no where condition
* 2. select aggr() ...; <- no group by * 2. select aggr() ...; <- no group by, no having
* 3. select ... limit 0/1;
* 4. select ... where rownum < 2;
* case 3 and 4 is not ignored at the present
*/ */
int ObTransformSimplify::check_subquery_valid(ObSelectStmt& stmt, bool& is_valid) int ObTransformSimplify::check_subquery_valid(ObSelectStmt& stmt, bool& is_valid)
{ {
int ret = OB_SUCCESS; int ret = OB_SUCCESS;
is_valid = false; is_valid = false;
int64_t limit = -1; ObRawExpr *sel_expr = NULL;
if (stmt.has_set_op() || stmt.is_hierarchical_query()) { if (stmt.is_set_stmt() || stmt.is_hierarchical_query()) {
// do nothing // do nothing
} else if (0 == stmt.get_from_item_size()) { } else {
is_valid = true;
} else if (OB_FAIL(ObTransformUtils::get_stmt_limit_value(stmt, limit))) {
LOG_WARN("failed to get stmt limit value", K(ret));
} else if (0 == limit || 1 == limit) {
is_valid = true;
} else if (0 == stmt.get_group_expr_size()) {
ObRawExpr* sel_expr = NULL;
if (OB_UNLIKELY(1 != stmt.get_select_item_size()) || OB_ISNULL(sel_expr = stmt.get_select_item(0).expr_)) { if (OB_UNLIKELY(1 != stmt.get_select_item_size()) || OB_ISNULL(sel_expr = stmt.get_select_item(0).expr_)) {
ret = OB_ERR_UNEXPECTED; ret = OB_ERR_UNEXPECTED;
LOG_WARN("get unexpected subquery", K(ret), K(stmt.get_select_item_size()), K(sel_expr)); LOG_WARN("get unexpected subquery", K(ret), K(stmt.get_select_item_size()), K(sel_expr));
} else if (sel_expr->has_flag(CNT_AGG)) { } else if (OB_NOT_NULL(stmt.get_limit_expr())) {
// do nothing
} else if (0 == stmt.get_from_item_size() && 0 == stmt.get_condition_size()) {
is_valid = true;
} else if (0 == stmt.get_group_expr_size() && 0 == stmt.get_having_expr_size() && sel_expr->has_flag(CNT_AGG)) {
is_valid = true; is_valid = true;
} }
} }