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Add support for deparsing semi-joins to contrib/postgres_fdw
SEMI-JOIN is deparsed as the EXISTS subquery. It references outer and inner relations, so it should be evaluated as the condition in the upper-level WHERE clause. The signatures of deparseFromExprForRel() and deparseRangeTblRef() are revised so that they can add conditions to the upper level. PgFdwRelationInfo now has a hidden_subquery_rels field, referencing the relids used in the inner parts of semi-join. They can't be referred to from upper relations and should be used internally for equivalence member searches. The planner can create semi-join, which refers to inner rel vars in its target list. However, we deparse semi-join as an exists() subquery. So we skip the case when the target list references to inner rel of semi-join. Author: Alexander Pyhalov Reviewed-by: Ashutosh Bapat, Ian Lawrence Barwick, Yuuki Fujii, Tomas Vondra Discussion: https://postgr.es/m/c9e2a757cf3ac2333714eaf83a9cc184@postgrespro.ru
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‎contrib/postgres_fdw/deparse.c

Lines changed: 188 additions & 46 deletions
Original file line numberDiff line numberDiff line change
@@ -180,11 +180,15 @@ static void appendConditions(List *exprs, deparse_expr_cxt *context);
180180
static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
181181
RelOptInfo *foreignrel, bool use_alias,
182182
Index ignore_rel, List **ignore_conds,
183+
List **additional_conds,
183184
List **params_list);
185+
static void appendWhereClause(List *exprs, List *additional_conds,
186+
deparse_expr_cxt *context);
184187
static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
185188
static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
186189
RelOptInfo *foreignrel, bool make_subquery,
187-
Index ignore_rel, List **ignore_conds, List **params_list);
190+
Index ignore_rel, List **ignore_conds,
191+
List **additional_conds, List **params_list);
188192
static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
189193
static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
190194
static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
@@ -1370,6 +1374,7 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
13701374
{
13711375
StringInfo buf = context->buf;
13721376
RelOptInfo *scanrel = context->scanrel;
1377+
List *additional_conds = NIL;
13731378

13741379
/* For upper relations, scanrel must be either a joinrel or a baserel */
13751380
Assert(!IS_UPPER_REL(context->foreignrel) ||
@@ -1379,14 +1384,11 @@ deparseFromExpr(List *quals, deparse_expr_cxt *context)
13791384
appendStringInfoString(buf, " FROM ");
13801385
deparseFromExprForRel(buf, context->root, scanrel,
13811386
(bms_membership(scanrel->relids) == BMS_MULTIPLE),
1382-
(Index) 0, NULL, context->params_list);
1383-
1384-
/* Construct WHERE clause */
1385-
if (quals != NIL)
1386-
{
1387-
appendStringInfoString(buf, " WHERE ");
1388-
appendConditions(quals, context);
1389-
}
1387+
(Index) 0, NULL, &additional_conds,
1388+
context->params_list);
1389+
appendWhereClause(quals, additional_conds, context);
1390+
if (additional_conds != NIL)
1391+
list_free_deep(additional_conds);
13901392
}
13911393

13921394
/*
@@ -1598,6 +1600,42 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
15981600
reset_transmission_modes(nestlevel);
15991601
}
16001602

1603+
/*
1604+
* Append WHERE clause, containing conditions from exprs and additional_conds,
1605+
* to context->buf.
1606+
*/
1607+
static void
1608+
appendWhereClause(List *exprs, List *additional_conds, deparse_expr_cxt *context)
1609+
{
1610+
StringInfo buf = context->buf;
1611+
bool need_and = false;
1612+
ListCell *lc;
1613+
1614+
if (exprs != NIL || additional_conds != NIL)
1615+
appendStringInfoString(buf, " WHERE ");
1616+
1617+
/*
1618+
* If there are some filters, append them.
1619+
*/
1620+
if (exprs != NIL)
1621+
{
1622+
appendConditions(exprs, context);
1623+
need_and = true;
1624+
}
1625+
1626+
/*
1627+
* If there are some EXISTS conditions, coming from SEMI-JOINS, append
1628+
* them.
1629+
*/
1630+
foreach(lc, additional_conds)
1631+
{
1632+
if (need_and)
1633+
appendStringInfoString(buf, " AND ");
1634+
appendStringInfoString(buf, (char *) lfirst(lc));
1635+
need_and = true;
1636+
}
1637+
}
1638+
16011639
/* Output join name for given join type */
16021640
const char *
16031641
get_jointype_name(JoinType jointype)
@@ -1616,6 +1654,9 @@ get_jointype_name(JoinType jointype)
16161654
case JOIN_FULL:
16171655
return "FULL";
16181656

1657+
case JOIN_SEMI:
1658+
return "SEMI";
1659+
16191660
default:
16201661
/* Shouldn't come here, but protect from buggy code. */
16211662
elog(ERROR, "unsupported join type %d", jointype);
@@ -1712,11 +1753,14 @@ deparseSubqueryTargetList(deparse_expr_cxt *context)
17121753
* of DELETE; it deparses the join relation as if the relation never contained
17131754
* the target relation, and creates a List of conditions to be deparsed into
17141755
* the top-level WHERE clause, which is returned to *ignore_conds.
1756+
*
1757+
* 'additional_conds' is a pointer to a list of strings to be appended to
1758+
* the WHERE clause, coming from lower-level SEMI-JOINs.
17151759
*/
17161760
static void
17171761
deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
17181762
bool use_alias, Index ignore_rel, List **ignore_conds,
1719-
List **params_list)
1763+
List **additional_conds, List **params_list)
17201764
{
17211765
PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
17221766

@@ -1728,6 +1772,8 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
17281772
RelOptInfo *innerrel = fpinfo->innerrel;
17291773
bool outerrel_is_target = false;
17301774
bool innerrel_is_target = false;
1775+
List *additional_conds_i = NIL;
1776+
List *additional_conds_o = NIL;
17311777

17321778
if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
17331779
{
@@ -1764,7 +1810,8 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
17641810
initStringInfo(&join_sql_o);
17651811
deparseRangeTblRef(&join_sql_o, root, outerrel,
17661812
fpinfo->make_outerrel_subquery,
1767-
ignore_rel, ignore_conds, params_list);
1813+
ignore_rel, ignore_conds, &additional_conds_o,
1814+
params_list);
17681815

17691816
/*
17701817
* If inner relation is the target relation, skip deparsing it.
@@ -1780,6 +1827,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
17801827
Assert(fpinfo->jointype == JOIN_INNER);
17811828
Assert(fpinfo->joinclauses == NIL);
17821829
appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
1830+
/* Pass EXISTS conditions to upper level */
1831+
if (additional_conds_o != NIL)
1832+
{
1833+
Assert(*additional_conds == NIL);
1834+
*additional_conds = additional_conds_o;
1835+
}
17831836
return;
17841837
}
17851838
}
@@ -1790,7 +1843,54 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
17901843
initStringInfo(&join_sql_i);
17911844
deparseRangeTblRef(&join_sql_i, root, innerrel,
17921845
fpinfo->make_innerrel_subquery,
1793-
ignore_rel, ignore_conds, params_list);
1846+
ignore_rel, ignore_conds, &additional_conds_i,
1847+
params_list);
1848+
1849+
/*
1850+
* SEMI-JOIN is deparsed as the EXISTS subquery. It references
1851+
* outer and inner relations, so it should be evaluated as the
1852+
* condition in the upper-level WHERE clause. We deparse the
1853+
* condition and pass it to upper level callers as an
1854+
* additional_conds list. Upper level callers are responsible for
1855+
* inserting conditions from the list where appropriate.
1856+
*/
1857+
if (fpinfo->jointype == JOIN_SEMI)
1858+
{
1859+
deparse_expr_cxt context;
1860+
StringInfoData str;
1861+
1862+
/* Construct deparsed condition from this SEMI-JOIN */
1863+
initStringInfo(&str);
1864+
appendStringInfo(&str, "EXISTS (SELECT NULL FROM %s",
1865+
join_sql_i.data);
1866+
1867+
context.buf = &str;
1868+
context.foreignrel = foreignrel;
1869+
context.scanrel = foreignrel;
1870+
context.root = root;
1871+
context.params_list = params_list;
1872+
1873+
/*
1874+
* Append SEMI-JOIN clauses and EXISTS conditions from lower
1875+
* levels to the current EXISTS subquery
1876+
*/
1877+
appendWhereClause(fpinfo->joinclauses, additional_conds_i, &context);
1878+
1879+
/*
1880+
* EXISTS conditions, coming from lower join levels, have just
1881+
* been processed.
1882+
*/
1883+
if (additional_conds_i != NIL)
1884+
{
1885+
list_free_deep(additional_conds_i);
1886+
additional_conds_i = NIL;
1887+
}
1888+
1889+
/* Close parentheses for EXISTS subquery */
1890+
appendStringInfo(&str, ")");
1891+
1892+
*additional_conds = lappend(*additional_conds, str.data);
1893+
}
17941894

17951895
/*
17961896
* If outer relation is the target relation, skip deparsing it.
@@ -1801,6 +1901,12 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
18011901
Assert(fpinfo->jointype == JOIN_INNER);
18021902
Assert(fpinfo->joinclauses == NIL);
18031903
appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
1904+
/* Pass EXISTS conditions to the upper call */
1905+
if (additional_conds_i != NIL)
1906+
{
1907+
Assert(*additional_conds == NIL);
1908+
*additional_conds = additional_conds_i;
1909+
}
18041910
return;
18051911
}
18061912
}
@@ -1809,33 +1915,65 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
18091915
Assert(!outerrel_is_target && !innerrel_is_target);
18101916

18111917
/*
1812-
* For a join relation FROM clause entry is deparsed as
1813-
*
1814-
* ((outer relation) <join type> (inner relation) ON (joinclauses))
1918+
* For semijoin FROM clause is deparsed as an outer relation. An inner
1919+
* relation and join clauses are converted to EXISTS condition and
1920+
* passed to the upper level.
18151921
*/
1816-
appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
1817-
get_jointype_name(fpinfo->jointype), join_sql_i.data);
1818-
1819-
/* Append join clause; (TRUE) if no join clause */
1820-
if (fpinfo->joinclauses)
1922+
if (fpinfo->jointype == JOIN_SEMI)
18211923
{
1822-
deparse_expr_cxt context;
1924+
appendStringInfo(buf, "%s", join_sql_o.data);
1925+
}
1926+
else
1927+
{
1928+
/*
1929+
* For a join relation FROM clause, entry is deparsed as
1930+
*
1931+
* ((outer relation) <join type> (inner relation) ON
1932+
* (joinclauses))
1933+
*/
1934+
appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
1935+
get_jointype_name(fpinfo->jointype), join_sql_i.data);
18231936

1824-
context.buf = buf;
1825-
context.foreignrel = foreignrel;
1826-
context.scanrel = foreignrel;
1827-
context.root = root;
1828-
context.params_list = params_list;
1937+
/* Append join clause; (TRUE) if no join clause */
1938+
if (fpinfo->joinclauses)
1939+
{
1940+
deparse_expr_cxt context;
18291941

1830-
appendStringInfoChar(buf, '(');
1831-
appendConditions(fpinfo->joinclauses, &context);
1942+
context.buf = buf;
1943+
context.foreignrel = foreignrel;
1944+
context.scanrel = foreignrel;
1945+
context.root = root;
1946+
context.params_list = params_list;
1947+
1948+
appendStringInfoChar(buf, '(');
1949+
appendConditions(fpinfo->joinclauses, &context);
1950+
appendStringInfoChar(buf, ')');
1951+
}
1952+
else
1953+
appendStringInfoString(buf, "(TRUE)");
1954+
1955+
/* End the FROM clause entry. */
18321956
appendStringInfoChar(buf, ')');
18331957
}
1834-
else
1835-
appendStringInfoString(buf, "(TRUE)");
18361958

1837-
/* End the FROM clause entry. */
1838-
appendStringInfoChar(buf, ')');
1959+
/*
1960+
* Construct additional_conds to be passed to the upper caller from
1961+
* current level additional_conds and additional_conds, coming from
1962+
* inner and outer rels.
1963+
*/
1964+
if (additional_conds_o != NIL)
1965+
{
1966+
*additional_conds = list_concat(*additional_conds,
1967+
additional_conds_o);
1968+
list_free(additional_conds_o);
1969+
}
1970+
1971+
if (additional_conds_i != NIL)
1972+
{
1973+
*additional_conds = list_concat(*additional_conds,
1974+
additional_conds_i);
1975+
list_free(additional_conds_i);
1976+
}
18391977
}
18401978
else
18411979
{
@@ -1863,11 +2001,13 @@ deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
18632001

18642002
/*
18652003
* Append FROM clause entry for the given relation into buf.
2004+
* Conditions from lower-level SEMI-JOINs are appended to additional_conds
2005+
* and should be added to upper level WHERE clause.
18662006
*/
18672007
static void
18682008
deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
18692009
bool make_subquery, Index ignore_rel, List **ignore_conds,
1870-
List **params_list)
2010+
List **additional_conds, List **params_list)
18712011
{
18722012
PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
18732013

@@ -1925,7 +2065,8 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
19252065
}
19262066
else
19272067
deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
1928-
ignore_conds, params_list);
2068+
ignore_conds, additional_conds,
2069+
params_list);
19292070
}
19302071

19312072
/*
@@ -2148,6 +2289,7 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
21482289
RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
21492290
ListCell *lc,
21502291
*lc2;
2292+
List *additional_conds = NIL;
21512293

21522294
/* Set up context struct for recursion */
21532295
context.root = root;
@@ -2189,17 +2331,17 @@ deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
21892331
{
21902332
List *ignore_conds = NIL;
21912333

2334+
21922335
appendStringInfoString(buf, " FROM ");
21932336
deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
2194-
&ignore_conds, params_list);
2337+
&ignore_conds, &additional_conds, params_list);
21952338
remote_conds = list_concat(remote_conds, ignore_conds);
21962339
}
21972340

2198-
if (remote_conds)
2199-
{
2200-
appendStringInfoString(buf, " WHERE ");
2201-
appendConditions(remote_conds, &context);
2202-
}
2341+
appendWhereClause(remote_conds, additional_conds, &context);
2342+
2343+
if (additional_conds != NIL)
2344+
list_free_deep(additional_conds);
22032345

22042346
if (foreignrel->reloptkind == RELOPT_JOINREL)
22052347
deparseExplicitTargetList(returningList, true, retrieved_attrs,
@@ -2255,6 +2397,7 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
22552397
List **retrieved_attrs)
22562398
{
22572399
deparse_expr_cxt context;
2400+
List *additional_conds = NIL;
22582401

22592402
/* Set up context struct for recursion */
22602403
context.root = root;
@@ -2274,15 +2417,14 @@ deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
22742417

22752418
appendStringInfoString(buf, " USING ");
22762419
deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
2277-
&ignore_conds, params_list);
2420+
&ignore_conds, &additional_conds, params_list);
22782421
remote_conds = list_concat(remote_conds, ignore_conds);
22792422
}
22802423

2281-
if (remote_conds)
2282-
{
2283-
appendStringInfoString(buf, " WHERE ");
2284-
appendConditions(remote_conds, &context);
2285-
}
2424+
appendWhereClause(remote_conds, additional_conds, &context);
2425+
2426+
if (additional_conds != NIL)
2427+
list_free_deep(additional_conds);
22862428

22872429
if (foreignrel->reloptkind == RELOPT_JOINREL)
22882430
deparseExplicitTargetList(returningList, true, retrieved_attrs,

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