1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
|
#include <Interpreters/PredicateExpressionsOptimizer.h>
#include <Interpreters/Context.h>
#include <Interpreters/ExtractExpressionInfoVisitor.h>
#include <Interpreters/PredicateRewriteVisitor.h>
#include <Interpreters/getTableExpressions.h>
#include <Interpreters/IdentifierSemantic.h>
#include <Parsers/ASTFunction.h>
#include <Parsers/ASTSelectQuery.h>
#include <Parsers/ASTSelectWithUnionQuery.h>
#include <Parsers/ASTTablesInSelectQuery.h>
#include <Parsers/IAST.h>
namespace DB
{
namespace ErrorCodes
{
extern const int LOGICAL_ERROR;
}
PredicateExpressionsOptimizer::PredicateExpressionsOptimizer(
ContextPtr context_, const TablesWithColumns & tables_with_columns_, const Settings & settings)
: WithContext(context_)
, enable_optimize_predicate_expression(settings.enable_optimize_predicate_expression)
, enable_optimize_predicate_expression_to_final_subquery(settings.enable_optimize_predicate_expression_to_final_subquery)
, allow_push_predicate_when_subquery_contains_with(settings.allow_push_predicate_when_subquery_contains_with)
, tables_with_columns(tables_with_columns_)
{
}
bool PredicateExpressionsOptimizer::optimize(ASTSelectQuery & select_query)
{
if (!enable_optimize_predicate_expression)
return false;
const bool has_incompatible_constructs = select_query.group_by_with_cube || select_query.group_by_with_rollup || select_query.group_by_with_totals || select_query.group_by_with_grouping_sets;
if (select_query.having() && !has_incompatible_constructs)
tryMovePredicatesFromHavingToWhere(select_query);
if (!select_query.tables() || select_query.tables()->children.empty())
return false;
if ((!select_query.where() && !select_query.prewhere()) || select_query.arrayJoinExpressionList().first)
return false;
const auto & tables_predicates = extractTablesPredicates(select_query.where(), select_query.prewhere());
if (!tables_predicates.empty())
return tryRewritePredicatesToTables(select_query.refTables()->children, tables_predicates);
return false;
}
std::vector<ASTs> PredicateExpressionsOptimizer::extractTablesPredicates(const ASTPtr & where, const ASTPtr & prewhere)
{
std::vector<ASTs> tables_predicates(tables_with_columns.size());
ASTs predicate_expressions;
splitConjunctionsAst(where, predicate_expressions);
splitConjunctionsAst(prewhere, predicate_expressions);
for (const auto & predicate_expression : predicate_expressions)
{
ExpressionInfoVisitor::Data expression_info{WithContext{getContext()}, tables_with_columns};
ExpressionInfoVisitor(expression_info).visit(predicate_expression);
if (expression_info.is_stateful_function
|| !expression_info.is_deterministic_function
|| expression_info.is_window_function)
{
return {}; /// Not optimized when predicate contains stateful function or indeterministic function or window functions
}
if (!expression_info.is_array_join)
{
if (expression_info.unique_reference_tables_pos.size() == 1)
tables_predicates[*expression_info.unique_reference_tables_pos.begin()].emplace_back(predicate_expression);
else if (expression_info.unique_reference_tables_pos.empty())
{
for (auto & predicate : tables_predicates)
predicate.emplace_back(predicate_expression);
}
}
}
return tables_predicates; /// everything is OK, it can be optimized
}
bool PredicateExpressionsOptimizer::tryRewritePredicatesToTables(ASTs & tables_element, const std::vector<ASTs> & tables_predicates)
{
bool is_rewrite_tables = false;
if (tables_element.size() != tables_predicates.size())
throw Exception(ErrorCodes::LOGICAL_ERROR,
"Unexpected elements count in predicate push down: "
"`set enable_optimize_predicate_expression = 0` to disable");
for (size_t index = tables_element.size(); index > 0; --index)
{
size_t table_pos = index - 1;
/// NOTE: the syntactic way of pushdown has limitations and should be partially disabled in case of JOINs.
/// Let's take a look at the query:
///
/// SELECT a, b FROM (SELECT 1 AS a) ANY LEFT JOIN (SELECT 1 AS a, 1 AS b) USING (a) WHERE b = 0
///
/// The result is empty - without pushdown. But the pushdown tends to modify it in this way:
///
/// SELECT a, b FROM (SELECT 1 AS a) ANY LEFT JOIN (SELECT 1 AS a, 1 AS b WHERE b = 0) USING (a) WHERE b = 0
///
/// That leads to the empty result in the right subquery and changes the whole outcome to (1, 0) or (1, NULL).
/// It happens because the not-matching columns are replaced with a global default values on JOIN.
/// Same is true for RIGHT JOIN and FULL JOIN.
if (const auto & table_element = tables_element[table_pos]->as<ASTTablesInSelectQueryElement>())
{
if (table_element->table_join && isLeft(table_element->table_join->as<ASTTableJoin>()->kind))
continue; /// Skip right table optimization
if (table_element->table_join && (
isFull(table_element->table_join->as<ASTTableJoin>()->kind)
|| table_element->table_join->as<ASTTableJoin>()->strictness == JoinStrictness::Asof
|| table_element->table_join->as<ASTTableJoin>()->strictness == JoinStrictness::Anti))
break; /// Skip left and right table optimization
is_rewrite_tables |= tryRewritePredicatesToTable(tables_element[table_pos], tables_predicates[table_pos],
tables_with_columns[table_pos]);
if (table_element->table_join && isRight(table_element->table_join->as<ASTTableJoin>()->kind))
break; /// Skip left table optimization
}
}
return is_rewrite_tables;
}
bool PredicateExpressionsOptimizer::tryRewritePredicatesToTable(ASTPtr & table_element, const ASTs & table_predicates, const TableWithColumnNamesAndTypes & table_columns) const
{
if (!table_predicates.empty())
{
auto optimize_final = enable_optimize_predicate_expression_to_final_subquery;
auto optimize_with = allow_push_predicate_when_subquery_contains_with;
PredicateRewriteVisitor::Data data(getContext(), table_predicates, table_columns, optimize_final, optimize_with);
PredicateRewriteVisitor(data).visit(table_element);
return data.is_rewrite;
}
return false;
}
bool PredicateExpressionsOptimizer::tryMovePredicatesFromHavingToWhere(ASTSelectQuery & select_query)
{
ASTs where_predicates;
ASTs having_predicates;
const auto & reduce_predicates = [&](const ASTs & predicates)
{
ASTPtr res = predicates[0];
for (size_t index = 1; index < predicates.size(); ++index)
res = makeASTFunction("and", res, predicates[index]);
return res;
};
for (const auto & moving_predicate : splitConjunctionsAst(select_query.having()))
{
TablesWithColumns tables;
ExpressionInfoVisitor::Data expression_info{WithContext{getContext()}, tables};
ExpressionInfoVisitor(expression_info).visit(moving_predicate);
/// TODO: If there is no group by, where, and prewhere expression, we can push down the stateful function
if (expression_info.is_stateful_function)
return false;
if (expression_info.is_window_function)
{
// Window functions are not allowed in either HAVING or WHERE.
return false;
}
if (expression_info.is_aggregate_function)
having_predicates.emplace_back(moving_predicate);
else
where_predicates.emplace_back(moving_predicate);
}
if (having_predicates.empty())
select_query.setExpression(ASTSelectQuery::Expression::HAVING, {});
else
{
auto having_predicate = reduce_predicates(having_predicates);
select_query.setExpression(ASTSelectQuery::Expression::HAVING, std::move(having_predicate));
}
if (!where_predicates.empty())
{
auto moved_predicate = reduce_predicates(where_predicates);
moved_predicate = select_query.where() ? makeASTFunction("and", select_query.where(), moved_predicate) : moved_predicate;
select_query.setExpression(ASTSelectQuery::Expression::WHERE, std::move(moved_predicate));
}
return true;
}
}
|
