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Avoid retrieving dummy NULL columns in postgres_fdw.
This should provide some marginal overall savings, since it surely takes many more cycles for the remote server to deal with the NULL columns than it takes for postgres_fdw not to emit them. But really the reason is to keep the emitted queries from looking quite so silly ...
This commit is contained in:
Tom Lane
@ -106,10 +106,12 @@ static void deparseTargetList(StringInfo buf,
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PlannerInfo *root,
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Index rtindex,
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Relation rel,
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Bitmapset *attrs_used);
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Bitmapset *attrs_used,
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List **retrieved_attrs);
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static void deparseReturningList(StringInfo buf, PlannerInfo *root,
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Index rtindex, Relation rel,
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List *returningList);
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List *returningList,
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List **retrieved_attrs);
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static void deparseColumnRef(StringInfo buf, int varno, int varattno,
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PlannerInfo *root);
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static void deparseRelation(StringInfo buf, Relation rel);
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@ -652,12 +654,16 @@ is_builtin(Oid oid)
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* Construct a simple SELECT statement that retrieves desired columns
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* of the specified foreign table, and append it to "buf". The output
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* contains just "SELECT ... FROM tablename".
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*
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* We also create an integer List of the columns being retrieved, which is
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* returned to *retrieved_attrs.
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*/
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void
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deparseSelectSql(StringInfo buf,
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PlannerInfo *root,
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RelOptInfo *baserel,
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Bitmapset *attrs_used)
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Bitmapset *attrs_used,
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List **retrieved_attrs)
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{
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RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);
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Relation rel;
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@ -672,7 +678,8 @@ deparseSelectSql(StringInfo buf,
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* Construct SELECT list
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*/
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appendStringInfoString(buf, "SELECT ");
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deparseTargetList(buf, root, baserel->relid, rel, attrs_used);
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deparseTargetList(buf, root, baserel->relid, rel, attrs_used,
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retrieved_attrs);
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/*
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* Construct FROM clause
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@ -687,24 +694,24 @@ deparseSelectSql(StringInfo buf,
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* Emit a target list that retrieves the columns specified in attrs_used.
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* This is used for both SELECT and RETURNING targetlists.
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*
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* We list attributes in order of the foreign table's columns, but replace
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* any attributes that need not be fetched with NULL constants. (We can't
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* just omit such attributes, or we'll lose track of which columns are
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* which at runtime.) Note however that any dropped columns are ignored.
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* Also, if ctid needs to be retrieved, it's added at the end.
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* The tlist text is appended to buf, and we also create an integer List
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* of the columns being retrieved, which is returned to *retrieved_attrs.
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*/
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static void
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deparseTargetList(StringInfo buf,
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PlannerInfo *root,
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Index rtindex,
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Relation rel,
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Bitmapset *attrs_used)
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Bitmapset *attrs_used,
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List **retrieved_attrs)
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{
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TupleDesc tupdesc = RelationGetDescr(rel);
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bool have_wholerow;
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bool first;
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int i;
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*retrieved_attrs = NIL;
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/* If there's a whole-row reference, we'll need all the columns. */
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have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
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attrs_used);
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@ -718,16 +725,18 @@ deparseTargetList(StringInfo buf,
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if (attr->attisdropped)
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continue;
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if (!first)
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appendStringInfoString(buf, ", ");
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first = false;
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if (have_wholerow ||
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bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
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attrs_used))
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{
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if (!first)
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appendStringInfoString(buf, ", ");
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first = false;
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deparseColumnRef(buf, rtindex, i, root);
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else
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appendStringInfoString(buf, "NULL");
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*retrieved_attrs = lappend_int(*retrieved_attrs, i);
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}
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}
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/*
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@ -742,6 +751,9 @@ deparseTargetList(StringInfo buf,
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first = false;
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appendStringInfoString(buf, "ctid");
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*retrieved_attrs = lappend_int(*retrieved_attrs,
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SelfItemPointerAttributeNumber);
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}
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/* Don't generate bad syntax if no undropped columns */
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@ -809,11 +821,16 @@ appendWhereClause(StringInfo buf,
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/*
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* deparse remote INSERT statement
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*
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* The statement text is appended to buf, and we also create an integer List
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* of the columns being retrieved by RETURNING (if any), which is returned
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* to *retrieved_attrs.
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*/
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void
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deparseInsertSql(StringInfo buf, PlannerInfo *root,
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Index rtindex, Relation rel,
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List *targetAttrs, List *returningList)
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List *targetAttrs, List *returningList,
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List **retrieved_attrs)
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{
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AttrNumber pindex;
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bool first;
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@ -858,16 +875,24 @@ deparseInsertSql(StringInfo buf, PlannerInfo *root,
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appendStringInfoString(buf, " DEFAULT VALUES");
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if (returningList)
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deparseReturningList(buf, root, rtindex, rel, returningList);
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deparseReturningList(buf, root, rtindex, rel, returningList,
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retrieved_attrs);
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else
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*retrieved_attrs = NIL;
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}
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/*
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* deparse remote UPDATE statement
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*
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* The statement text is appended to buf, and we also create an integer List
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* of the columns being retrieved by RETURNING (if any), which is returned
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* to *retrieved_attrs.
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*/
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void
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deparseUpdateSql(StringInfo buf, PlannerInfo *root,
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Index rtindex, Relation rel,
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List *targetAttrs, List *returningList)
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List *targetAttrs, List *returningList,
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List **retrieved_attrs)
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{
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AttrNumber pindex;
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bool first;
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@ -894,23 +919,34 @@ deparseUpdateSql(StringInfo buf, PlannerInfo *root,
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appendStringInfoString(buf, " WHERE ctid = $1");
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if (returningList)
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deparseReturningList(buf, root, rtindex, rel, returningList);
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deparseReturningList(buf, root, rtindex, rel, returningList,
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retrieved_attrs);
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else
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*retrieved_attrs = NIL;
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}
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/*
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* deparse remote DELETE statement
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*
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* The statement text is appended to buf, and we also create an integer List
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* of the columns being retrieved by RETURNING (if any), which is returned
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* to *retrieved_attrs.
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*/
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void
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deparseDeleteSql(StringInfo buf, PlannerInfo *root,
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Index rtindex, Relation rel,
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List *returningList)
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List *returningList,
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List **retrieved_attrs)
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{
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appendStringInfoString(buf, "DELETE FROM ");
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deparseRelation(buf, rel);
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appendStringInfoString(buf, " WHERE ctid = $1");
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if (returningList)
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deparseReturningList(buf, root, rtindex, rel, returningList);
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deparseReturningList(buf, root, rtindex, rel, returningList,
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retrieved_attrs);
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else
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*retrieved_attrs = NIL;
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}
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/*
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@ -919,7 +955,8 @@ deparseDeleteSql(StringInfo buf, PlannerInfo *root,
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static void
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deparseReturningList(StringInfo buf, PlannerInfo *root,
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Index rtindex, Relation rel,
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List *returningList)
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List *returningList,
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List **retrieved_attrs)
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{
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Bitmapset *attrs_used;
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@ -931,7 +968,8 @@ deparseReturningList(StringInfo buf, PlannerInfo *root,
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&attrs_used);
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appendStringInfoString(buf, " RETURNING ");
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deparseTargetList(buf, root, rtindex, rel, attrs_used);
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deparseTargetList(buf, root, rtindex, rel, attrs_used,
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retrieved_attrs);
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}
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/*
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@ -959,10 +997,11 @@ deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
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/*
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* Construct SELECT statement to acquire sample rows of given relation.
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*
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* Note: command is appended to whatever might be in buf already.
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* SELECT command is appended to buf, and list of columns retrieved
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* is returned to *retrieved_attrs.
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*/
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void
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deparseAnalyzeSql(StringInfo buf, Relation rel)
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deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
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{
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Oid relid = RelationGetRelid(rel);
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TupleDesc tupdesc = RelationGetDescr(rel);
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@ -972,6 +1011,8 @@ deparseAnalyzeSql(StringInfo buf, Relation rel)
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ListCell *lc;
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bool first = true;
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*retrieved_attrs = NIL;
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appendStringInfoString(buf, "SELECT ");
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for (i = 0; i < tupdesc->natts; i++)
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{
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@ -999,6 +1040,8 @@ deparseAnalyzeSql(StringInfo buf, Relation rel)
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}
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appendStringInfoString(buf, quote_identifier(colname));
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*retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
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}
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/* Don't generate bad syntax for zero-column relation. */
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