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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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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),