Details
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Bug
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Status: In Review (View Workflow)
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Major
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Resolution: Unresolved
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12.2
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None
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Can result in unexpected behaviour
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Q4/2025 Server Development
Description
The following query doesn't mark its union's cacheable flag as UNCACHEABLE_RAND:
create table t1 (a int); |
create table t2 select * from t1 where 1 in (select 1 union select 2 union select RAND()); |
However there's no problem with the following query:
select * from t1 where 1 in (select 1 union select RAND()); |
As described by psergei in this PR comment thread, the problem begins from:
(gdb) wher 10
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#0 st_select_lex_unit::register_select_chain (this=0x7fff1c017e28, first_sel=0x7fff1c0178c0) at /home/psergey/dev-git2/10.11-look/sql/sql_lex.cc:10117
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#1 0x0000555555f652d2 in LEX::create_unit (this=0x7fff1c005168, first_sel=0x7fff1c0178c0) at /home/psergey/dev-git2/10.11-look/sql/sql_lex.cc:6275
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#2 0x0000555555f74c17 in LEX::parsed_select_expr_start (this=0x7fff1c005168, s1=0x7fff1c0178c0, s2=0x7fff1c018658, unit_type=UNION_TYPE, distinct=true) at /home/psergey/dev-git2/10.11-look/sql/sql_lex.cc:10388
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#3 0x0000555555f74f81 in LEX::add_primary_to_query_expression_body (this=0x7fff1c005168, unit=0x7fff1c017e28, sel=0x7fff1c018658, unit_type=UNION_TYPE, distinct=true, oracle=false) at /home/psergey/dev-git2/10.11-look/sql/sql_lex.cc:10458
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#4 0x0000555555f75017 in LEX::add_primary_to_query_expression_body (this=0x7fff1c005168, unit=0x7fff1c017e28, sel=0x7fff1c018658, unit_type=UNION_TYPE, distinct=true) at /home/ psergey/dev-git2/10.11-look/sql/sql_lex.cc:10473
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#5 0x00005555562c2136 in MYSQLparse (thd=0x7fff1c000d78) at /home/psergey/dev-git2/10.11-look/sql/sql_yacc.yy:8774 |
in LEX::add_primary_to_query_expression_body() there are two codepaths:
if (!sel1->next_select()) |
unit= parsed_select_expr_start(sel1, sel2, unit_type, distinct);
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else |
unit= parsed_select_expr_cont(unit, sel2, unit_type, distinct, oracle);
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if-branch is taken for the first two UNION members. else-branch is for the rest.
Then, parsed_select_expr_cont() calls create_unit() (which doesn't really create it for the second member), which calls
unit->register_select_chain(first_sel);
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which propagates the uncacheable flag from UNION members to the SELECT_LEX_UNIT object. LEX::parsed_select_expr_cont() just doesn't do this.
Attachments
Issue Links
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- Closed
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