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TABLESAMPLE, SQL Standard and extensible

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Add a TABLESAMPLE clause to SELECT statements that allows
user to specify random BERNOULLI sampling or block level
SYSTEM sampling. Implementation allows for extensible
sampling functions to be written, using a standard API.
Basic version follows SQLStandard exactly. Usable
concrete use cases for the sampling API follow in later
commits.

Petr Jelinek

Reviewed by Michael Paquier and Simon Riggs
This commit is contained in:
Simon Riggs
2015-05-15 14:37:10 -04:00
parent 11a83bbedd
commit f6d208d6e5
66 changed files with 2756 additions and 40 deletions
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28
src/backend/nodes/nodeFuncs.c
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@ -2058,6 +2058,14 @@ range_table_walker(List *rtable,
switch (rte->rtekind)
{
case RTE_RELATION:
if (rte->tablesample)
{
if (walker(rte->tablesample->args, context))
return true;
if (walker(rte->tablesample->repeatable, context))
return true;
}
break;
case RTE_CTE:
/* nothing to do */
break;
@ -2813,6 +2821,14 @@ range_table_mutator(List *rtable,
switch (rte->rtekind)
{
case RTE_RELATION:
if (rte->tablesample)
{
MUTATE(rte->tablesample->args, rte->tablesample->args,
List *);
MUTATE(rte->tablesample->repeatable,
rte->tablesample->repeatable, Node *);
}
break;
case RTE_CTE:
/* we don't bother to copy eref, aliases, etc; OK? */
break;
@ -3309,6 +3325,18 @@ raw_expression_tree_walker(Node *node,
break;
case T_CommonTableExpr:
return walker(((CommonTableExpr *) node)->ctequery, context);
case T_RangeTableSample:
{
RangeTableSample *rts = (RangeTableSample *) node;
if (walker(rts->relation, context))
return true;
if (walker(rts->repeatable, context))
return true;
if (walker(rts->args, context))
return true;
}
break;
default:
elog(ERROR, "unrecognized node type: %d",
(int) nodeTag(node));