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Sanitize IF NOT EXISTS in EXPLAIN for CTAS and matviews

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IF NOT EXISTS was ignored when specified in an EXPLAIN query for CREATE
MATERIALIZED VIEW or CREATE TABLE AS.  Hence, if this clause was
specified, the caller would get a failure if the relation already
exists instead of a success with a NOTICE message.

This commit makes the behavior of IF NOT EXISTS in EXPLAIN consistent
with the non-EXPLAIN'd DDL queries, preventing a failure with IF NOT
EXISTS if the relation to-be-created already exists.  The skip is done
before the SELECT query used for the relation is planned or executed,
and a "dummy" plan is generated instead depending on the format used by
EXPLAIN.

Author: Bharath Rupireddy
Reviewed-by: Zhijie Hou, Michael Paquier
Discussion: https://postgr.es/m/CALj2ACVa3oJ9O_wcGd+FtHWZds04dEKcakxphGz5POVgD4wC7Q@mail.gmail.com
This commit is contained in:
Michael Paquier
2020-12-30 21:23:24 +09:00
parent 0aa8a01d04
commit e665769e6d
7 changed files with 180 additions and 15 deletions
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53
src/backend/commands/createas.c
View File

@ -239,21 +239,9 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
PlannedStmt *plan;
QueryDesc *queryDesc;
if (stmt->if_not_exists)
{
Oid nspid;
nspid = RangeVarGetCreationNamespace(stmt->into->rel);
if (get_relname_relid(stmt->into->rel->relname, nspid))
{
ereport(NOTICE,
(errcode(ERRCODE_DUPLICATE_TABLE),
errmsg("relation \"%s\" already exists, skipping",
stmt->into->rel->relname)));
return InvalidObjectAddress;
}
}
/* Check if the relation exists or not */
if (CreateTableAsRelExists(stmt))
return InvalidObjectAddress;
/*
* Create the tuple receiver object and insert info it will need
@ -400,6 +388,41 @@ GetIntoRelEFlags(IntoClause *intoClause)
return flags;
}
/*
* CreateTableAsRelExists --- check existence of relation for CreateTableAsStmt
*
* Utility wrapper checking if the relation pending for creation in this
* CreateTableAsStmt query already exists or not. Returns true if the
* relation exists, otherwise false.
*/
bool
CreateTableAsRelExists(CreateTableAsStmt *ctas)
{
Oid nspid;
IntoClause *into = ctas->into;
nspid = RangeVarGetCreationNamespace(into->rel);
if (get_relname_relid(into->rel->relname, nspid))
{
if (!ctas->if_not_exists)
ereport(ERROR,
(errcode(ERRCODE_DUPLICATE_TABLE),
errmsg("relation \"%s\" already exists",
into->rel->relname)));
/* The relation exists and IF NOT EXISTS has been specified */
ereport(NOTICE,
(errcode(ERRCODE_DUPLICATE_TABLE),
errmsg("relation \"%s\" already exists, skipping",
into->rel->relname)));
return true;
}
/* Relation does not exist, it can be created */
return false;
}
/*
* CreateIntoRelDestReceiver -- create a suitable DestReceiver object
*

16
src/backend/commands/explain.c
View File

@ -435,6 +435,22 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
CreateTableAsStmt *ctas = (CreateTableAsStmt *) utilityStmt;
List *rewritten;
/*
* Check if the relation exists or not. This is done at this stage to
* avoid query planning or execution.
*/
if (CreateTableAsRelExists(ctas))
{
if (ctas->objtype == OBJECT_TABLE)
ExplainDummyGroup("CREATE TABLE AS", NULL, es);
else if (ctas->objtype == OBJECT_MATVIEW)
ExplainDummyGroup("CREATE MATERIALIZED VIEW", NULL, es);
else
elog(ERROR, "unexpected object type: %d",
(int) ctas->objtype);
return;
}
rewritten = QueryRewrite(castNode(Query, copyObject(ctas->query)));
Assert(list_length(rewritten) == 1);
ExplainOneQuery(linitial_node(Query, rewritten),