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MDEV-22042 Server crash in Item_field::print on ANALYZE FORMAT=JSON
When processing a query with a recursive CTE a temporary table is used for each recursive reference of the CTE. As any temporary table it uses its own mem-root for table definition structures. Due to specifics of the current implementation of ANALYZE stmt command this mem-root can be freed only at the very of query processing. Such deallocation of mem-root memory happens in close_thread_tables(). The function looks through the list of the tmp tables rec_tables attached to the THD of the query and frees corresponding mem-roots. If the query uses a stored function then such list is created for each query of the function. When a new rec_list has to be created the old one has to be saved and then restored at the proper moment. The bug occurred because only one rec_list for the query containing CTE was created. As a result close_thread_tables() freed tmp mem-roots used for rec_tables prematurely destroying some data needed for the output produced by the ANALYZE command.
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‎mysql-test/r/cte_recursive.result‎

Lines changed: 162 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3648,3 +3648,165 @@ select * from t1 as t;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t ALL NULL NULL NULL NULL 4
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drop table t1,t2;
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#
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# MDEV-22042: ANALYZE of query using stored function and recursive CTE
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#
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create table t1 (a1 varchar(20),a2 varchar(20)) engine=myisam;
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insert into t1 values (1,1),(2,2),(3,3);
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create table t2 (
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a2 varchar(20) primary key, b1 varchar(20), key (b1)
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) engine=myisam;
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insert into t2 values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7);
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insert into t2 values (11,11),(12,12),(13,13),(14,14),(15,15),(16,16),(17,17);
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create function f1(id varchar(20)) returns varchar(50)
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begin
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declare res varchar (50);
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select a2 into res from t2 where a2=id and b1=1 limit 1;
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return res;
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end$$
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select fv
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from (select t1.a1, f1(t1.a2) fv from t1) dt
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where (dt.a1) in (with recursive cte as (select a2 from t2 where a2='2'
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union select tt2.a2 from t2 tt2 join cte on tt2.b1=cte.a2)
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select a2 from cte);
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fv
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NULL
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explain select fv
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from (select t1.a1, f1(t1.a2) fv from t1) dt
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where (dt.a1) in (with recursive cte as (select a2 from t2 where a2='2'
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union select tt2.a2 from t2 tt2 join cte on tt2.b1=cte.a2)
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select a2 from cte);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY <subquery3> ALL distinct_key NULL NULL NULL 2
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1 PRIMARY t1 ALL NULL NULL NULL NULL 3 Using where; Using join buffer (flat, BNL join)
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3 MATERIALIZED <derived4> ALL NULL NULL NULL NULL 2
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4 DERIVED t2 const PRIMARY PRIMARY 22 const 1 Using index
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5 RECURSIVE UNION <derived4> ALL NULL NULL NULL NULL 2
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5 RECURSIVE UNION tt2 ref b1 b1 23 cte.a2 2
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NULL UNION RESULT <union4,5> ALL NULL NULL NULL NULL NULL
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analyze format=json select fv
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from (select t1.a1, f1(t1.a2) fv from t1) dt
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where (dt.a1) in (with recursive cte as (select a2 from t2 where a2='2'
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union select tt2.a2 from t2 tt2 join cte on tt2.b1=cte.a2)
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select a2 from cte);
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ANALYZE
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{
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"query_block": {
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"select_id": 1,
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"r_loops": 1,
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"r_total_time_ms": "REPLACED",
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"table": {
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"table_name": "<subquery3>",
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"access_type": "ALL",
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"possible_keys": ["distinct_key"],
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"r_loops": 1,
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"rows": 2,
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"r_rows": 1,
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"r_total_time_ms": "REPLACED",
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"filtered": 100,
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"r_filtered": 100,
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"materialized": {
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"unique": 1,
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"query_block": {
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"select_id": 3,
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"table": {
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"table_name": "<derived4>",
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"access_type": "ALL",
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"r_loops": 1,
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"rows": 2,
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"r_rows": 1,
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"r_total_time_ms": "REPLACED",
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"filtered": 100,
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"r_filtered": 100,
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"materialized": {
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"query_block": {
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"recursive_union": {
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"table_name": "<union4,5>",
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"access_type": "ALL",
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"r_loops": 0,
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"r_rows": null,
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"query_specifications": [
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{
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"query_block": {
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"select_id": 4,
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"r_loops": 1,
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"r_total_time_ms": "REPLACED",
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"table": {
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"table_name": "t2",
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"access_type": "const",
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"possible_keys": ["PRIMARY"],
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"key": "PRIMARY",
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"key_length": "22",
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"used_key_parts": ["a2"],
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"ref": ["const"],
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"r_loops": 0,
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"rows": 1,
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"r_rows": null,
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"filtered": 100,
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"r_filtered": null,
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"using_index": true
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}
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}
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},
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{
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"query_block": {
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"select_id": 5,
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"r_loops": 1,
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"r_total_time_ms": "REPLACED",
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"table": {
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"table_name": "<derived4>",
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"access_type": "ALL",
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"r_loops": 1,
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"rows": 2,
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"r_rows": 1,
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"r_total_time_ms": "REPLACED",
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"filtered": 100,
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"r_filtered": 100
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},
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"table": {
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"table_name": "tt2",
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"access_type": "ref",
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"possible_keys": ["b1"],
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"key": "b1",
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"key_length": "23",
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"used_key_parts": ["b1"],
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"ref": ["cte.a2"],
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"r_loops": 1,
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"rows": 2,
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"r_rows": 1,
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"r_total_time_ms": "REPLACED",
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"filtered": 100,
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"r_filtered": 100
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}
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}
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}
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]
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}
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}
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}
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}
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}
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}
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},
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"block-nl-join": {
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"table": {
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"table_name": "t1",
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"access_type": "ALL",
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"r_loops": 1,
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"rows": 3,
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"r_rows": 3,
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"r_total_time_ms": "REPLACED",
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"filtered": 100,
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"r_filtered": 100
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},
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"buffer_type": "flat",
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"buffer_size": "256Kb",
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"join_type": "BNL",
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"attached_condition": "t1.a1 = cte.a2",
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"r_filtered": 33.333
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}
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}
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}
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drop function f1;
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drop table t1,t2;
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End of 10.2 tests

‎mysql-test/t/cte_recursive.test‎

Lines changed: 39 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2536,3 +2536,42 @@ with recursive cte as
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select * from t1 as t;
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drop table t1,t2;
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--echo #
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--echo # MDEV-22042: ANALYZE of query using stored function and recursive CTE
2542+
--echo #
2543+
2544+
create table t1 (a1 varchar(20),a2 varchar(20)) engine=myisam;
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insert into t1 values (1,1),(2,2),(3,3);
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create table t2 (
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a2 varchar(20) primary key, b1 varchar(20), key (b1)
2549+
) engine=myisam;
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insert into t2 values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7);
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insert into t2 values (11,11),(12,12),(13,13),(14,14),(15,15),(16,16),(17,17);
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delimiter $$;
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create function f1(id varchar(20)) returns varchar(50)
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begin
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declare res varchar (50);
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select a2 into res from t2 where a2=id and b1=1 limit 1;
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return res;
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end$$
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delimiter ;$$
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let q=
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select fv
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from (select t1.a1, f1(t1.a2) fv from t1) dt
2565+
where (dt.a1) in (with recursive cte as (select a2 from t2 where a2='2'
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union select tt2.a2 from t2 tt2 join cte on tt2.b1=cte.a2)
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select a2 from cte);
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eval $q;
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eval explain $q;
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--source include/analyze-format.inc
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eval analyze format=json $q;
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drop function f1;
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drop table t1,t2;
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--echo End of 10.2 tests

‎sql/sp_head.cc‎

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1126,6 +1126,7 @@ sp_head::execute(THD *thd, bool merge_da_on_success)
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backup_arena;
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query_id_t old_query_id;
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TABLE *old_derived_tables;
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TABLE *old_rec_tables;
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LEX *old_lex;
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Item_change_list old_change_list;
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String old_packet;
@@ -1201,6 +1202,8 @@ sp_head::execute(THD *thd, bool merge_da_on_success)
12011202
old_query_id= thd->query_id;
12021203
old_derived_tables= thd->derived_tables;
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thd->derived_tables= 0;
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old_rec_tables= thd->rec_tables;
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thd->rec_tables= 0;
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save_sql_mode= thd->variables.sql_mode;
12051208
thd->variables.sql_mode= m_sql_mode;
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save_abort_on_warning= thd->abort_on_warning;
@@ -1468,6 +1471,7 @@ sp_head::execute(THD *thd, bool merge_da_on_success)
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thd->set_query_id(old_query_id);
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DBUG_ASSERT(!thd->derived_tables);
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thd->derived_tables= old_derived_tables;
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thd->rec_tables= old_rec_tables;
14711475
thd->variables.sql_mode= save_sql_mode;
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thd->abort_on_warning= save_abort_on_warning;
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thd->m_reprepare_observer= save_reprepare_observer;

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