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postgresql/src/backend/commands/view.c
Tom Lane 1281a5c907 Restructure ALTER TABLE execution to fix assorted bugs. 
We've had numerous bug reports about how (1) IF NOT EXISTS clauses in
ALTER TABLE don't behave as-expected, and (2) combining certain actions
into one ALTER TABLE doesn't work, though executing the same actions as
separate statements does.  This patch cleans up all of the cases so far
reported from the field, though there are still some oddities associated
with identity columns.

The core problem behind all of these bugs is that we do parse analysis
of ALTER TABLE subcommands too soon, before starting execution of the
statement.  The root of the bugs in group (1) is that parse analysis
schedules derived commands (such as a CREATE SEQUENCE for a serial
column) before it's known whether the IF NOT EXISTS clause should cause
a subcommand to be skipped.  The root of the bugs in group (2) is that
earlier subcommands may change the catalog state that later subcommands
need to be parsed against.

Hence, postpone parse analysis of ALTER TABLE's subcommands, and do
that one subcommand at a time, during "phase 2" of ALTER TABLE which
is the phase that does catalog rewrites.  Thus the catalog effects
of earlier subcommands are already visible when we analyze later ones.
(The sole exception is that we do parse analysis for ALTER COLUMN TYPE
subcommands during phase 1, so that their USING expressions can be
parsed against the table's original state, which is what we need.
Arguably, these bugs stem from falsely concluding that because ALTER
COLUMN TYPE must do early parse analysis, every other command subtype
can too.)

This means that ALTER TABLE itself must deal with execution of any
non-ALTER-TABLE derived statements that are generated by parse analysis.
Add a suitable entry point to utility.c to accept those recursive
calls, and create a struct to pass through the information needed by
the recursive call, rather than making the argument lists of
AlterTable() and friends even longer.

Getting this to work correctly required a little bit of fiddling
with the subcommand pass structure, in particular breaking up
AT_PASS_ADD_CONSTR into multiple passes.  But otherwise it's mostly
a pretty straightforward application of the above ideas.

Fixing the residual issues for identity columns requires refactoring of
where the dependency link from an identity column to its sequence gets
set up.  So that seems like suitable material for a separate patch,
especially since this one is pretty big already.

Discussion: https://postgr.es/m/10365.1558909428@sss.pgh.pa.us
2020-01-15 18:49:24 -05:00

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/*-------------------------------------------------------------------------
*
* view.c
* use rewrite rules to construct views
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/commands/view.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/relation.h"
#include "access/xact.h"
#include "catalog/namespace.h"
#include "commands/defrem.h"
#include "commands/tablecmds.h"
#include "commands/view.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "parser/analyze.h"
#include "parser/parse_relation.h"
#include "rewrite/rewriteDefine.h"
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "rewrite/rewriteSupport.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"
static void checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc);
/*---------------------------------------------------------------------
* DefineVirtualRelation
*
* Create a view relation and use the rules system to store the query
* for the view.
*
* EventTriggerAlterTableStart must have been called already.
*---------------------------------------------------------------------
*/
static ObjectAddress
DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
List *options, Query *viewParse)
{
Oid viewOid;
LOCKMODE lockmode;
CreateStmt *createStmt = makeNode(CreateStmt);
List *attrList;
ListCell *t;
/*
* create a list of ColumnDef nodes based on the names and types of the
* (non-junk) targetlist items from the view's SELECT list.
*/
attrList = NIL;
foreach(t, tlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(t);
if (!tle->resjunk)
{
ColumnDef *def = makeColumnDef(tle->resname,
exprType((Node *) tle->expr),
exprTypmod((Node *) tle->expr),
exprCollation((Node *) tle->expr));
/*
* It's possible that the column is of a collatable type but the
* collation could not be resolved, so double-check.
*/
if (type_is_collatable(exprType((Node *) tle->expr)))
{
if (!OidIsValid(def->collOid))
ereport(ERROR,
(errcode(ERRCODE_INDETERMINATE_COLLATION),
errmsg("could not determine which collation to use for view column \"%s\"",
def->colname),
errhint("Use the COLLATE clause to set the collation explicitly.")));
}
else
Assert(!OidIsValid(def->collOid));
attrList = lappend(attrList, def);
}
}
/*
* Look up, check permissions on, and lock the creation namespace; also
* check for a preexisting view with the same name. This will also set
* relation->relpersistence to RELPERSISTENCE_TEMP if the selected
* namespace is temporary.
*/
lockmode = replace ? AccessExclusiveLock : NoLock;
(void) RangeVarGetAndCheckCreationNamespace(relation, lockmode, &viewOid);
if (OidIsValid(viewOid) && replace)
{
Relation rel;
TupleDesc descriptor;
List *atcmds = NIL;
AlterTableCmd *atcmd;
ObjectAddress address;
/* Relation is already locked, but we must build a relcache entry. */
rel = relation_open(viewOid, NoLock);
/* Make sure it *is* a view. */
if (rel->rd_rel->relkind != RELKIND_VIEW)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("\"%s\" is not a view",
RelationGetRelationName(rel))));
/* Also check it's not in use already */
CheckTableNotInUse(rel, "CREATE OR REPLACE VIEW");
/*
* Due to the namespace visibility rules for temporary objects, we
* should only end up replacing a temporary view with another
* temporary view, and similarly for permanent views.
*/
Assert(relation->relpersistence == rel->rd_rel->relpersistence);
/*
* Create a tuple descriptor to compare against the existing view, and
* verify that the old column list is an initial prefix of the new
* column list.
*/
descriptor = BuildDescForRelation(attrList);
checkViewTupleDesc(descriptor, rel->rd_att);
/*
* If new attributes have been added, we must add pg_attribute entries
* for them. It is convenient (although overkill) to use the ALTER
* TABLE ADD COLUMN infrastructure for this.
*
* Note that we must do this before updating the query for the view,
* since the rules system requires that the correct view columns be in
* place when defining the new rules.
*
* Also note that ALTER TABLE doesn't run parse transformation on
* AT_AddColumnToView commands. The ColumnDef we supply must be ready
* to execute as-is.
*/
if (list_length(attrList) > rel->rd_att->natts)
{
ListCell *c;
int skip = rel->rd_att->natts;
foreach(c, attrList)
{
if (skip > 0)
{
skip--;
continue;
}
atcmd = makeNode(AlterTableCmd);
atcmd->subtype = AT_AddColumnToView;
atcmd->def = (Node *) lfirst(c);
atcmds = lappend(atcmds, atcmd);
}
/* EventTriggerAlterTableStart called by ProcessUtilitySlow */
AlterTableInternal(viewOid, atcmds, true);
/* Make the new view columns visible */
CommandCounterIncrement();
}
/*
* Update the query for the view.
*
* Note that we must do this before updating the view options, because
* the new options may not be compatible with the old view query (for
* example if we attempt to add the WITH CHECK OPTION, we require that
* the new view be automatically updatable, but the old view may not
* have been).
*/
StoreViewQuery(viewOid, viewParse, replace);
/* Make the new view query visible */
CommandCounterIncrement();
/*
* Finally update the view options.
*
* The new options list replaces the existing options list, even if
* it's empty.
*/
atcmd = makeNode(AlterTableCmd);
atcmd->subtype = AT_ReplaceRelOptions;
atcmd->def = (Node *) options;
atcmds = list_make1(atcmd);
/* EventTriggerAlterTableStart called by ProcessUtilitySlow */
AlterTableInternal(viewOid, atcmds, true);
ObjectAddressSet(address, RelationRelationId, viewOid);
/*
* Seems okay, so return the OID of the pre-existing view.
*/
relation_close(rel, NoLock); /* keep the lock! */
return address;
}
else
{
ObjectAddress address;
/*
* Set the parameters for keys/inheritance etc. All of these are
* uninteresting for views...
*/
createStmt->relation = relation;
createStmt->tableElts = attrList;
createStmt->inhRelations = NIL;
createStmt->constraints = NIL;
createStmt->options = options;
createStmt->oncommit = ONCOMMIT_NOOP;
createStmt->tablespacename = NULL;
createStmt->if_not_exists = false;
/*
* Create the relation (this will error out if there's an existing
* view, so we don't need more code to complain if "replace" is
* false).
*/
address = DefineRelation(createStmt, RELKIND_VIEW, InvalidOid, NULL,
NULL);
Assert(address.objectId != InvalidOid);
/* Make the new view relation visible */
CommandCounterIncrement();
/* Store the query for the view */
StoreViewQuery(address.objectId, viewParse, replace);
return address;
}
}
/*
* Verify that tupledesc associated with proposed new view definition
* matches tupledesc of old view. This is basically a cut-down version
* of equalTupleDescs(), with code added to generate specific complaints.
* Also, we allow the new tupledesc to have more columns than the old.
*/
static void
checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
{
int i;
if (newdesc->natts < olddesc->natts)
ereport(ERROR,
(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
errmsg("cannot drop columns from view")));
for (i = 0; i < olddesc->natts; i++)
{
Form_pg_attribute newattr = TupleDescAttr(newdesc, i);
Form_pg_attribute oldattr = TupleDescAttr(olddesc, i);
/* XXX msg not right, but we don't support DROP COL on view anyway */
if (newattr->attisdropped != oldattr->attisdropped)
ereport(ERROR,
(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
errmsg("cannot drop columns from view")));
if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
ereport(ERROR,
(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
errmsg("cannot change name of view column \"%s\" to \"%s\"",
NameStr(oldattr->attname),
NameStr(newattr->attname)),
errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
/* XXX would it be safe to allow atttypmod to change? Not sure */
if (newattr->atttypid != oldattr->atttypid ||
newattr->atttypmod != oldattr->atttypmod)
ereport(ERROR,
(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
errmsg("cannot change data type of view column \"%s\" from %s to %s",
NameStr(oldattr->attname),
format_type_with_typemod(oldattr->atttypid,
oldattr->atttypmod),
format_type_with_typemod(newattr->atttypid,
newattr->atttypmod))));
/* We can ignore the remaining attributes of an attribute... */
}
/*
* We ignore the constraint fields. The new view desc can't have any
* constraints, and the only ones that could be on the old view are
* defaults, which we are happy to leave in place.
*/
}
static void
DefineViewRules(Oid viewOid, Query *viewParse, bool replace)
{
/*
* Set up the ON SELECT rule. Since the query has already been through
* parse analysis, we use DefineQueryRewrite() directly.
*/
DefineQueryRewrite(pstrdup(ViewSelectRuleName),
viewOid,
NULL,
CMD_SELECT,
true,
replace,
list_make1(viewParse));
/*
* Someday: automatic ON INSERT, etc
*/
}
/*---------------------------------------------------------------
* UpdateRangeTableOfViewParse
*
* Update the range table of the given parsetree.
* This update consists of adding two new entries IN THE BEGINNING
* of the range table (otherwise the rule system will die a slow,
* horrible and painful death, and we do not want that now, do we?)
* one for the OLD relation and one for the NEW one (both of
* them refer in fact to the "view" relation).
*
* Of course we must also increase the 'varnos' of all the Var nodes
* by 2...
*
* These extra RT entries are not actually used in the query,
* except for run-time locking and permission checking.
*---------------------------------------------------------------
*/
static Query *
UpdateRangeTableOfViewParse(Oid viewOid, Query *viewParse)
{
Relation viewRel;
List *new_rt;
ParseNamespaceItem *nsitem;
RangeTblEntry *rt_entry1,
*rt_entry2;
ParseState *pstate;
/*
* Make a copy of the given parsetree. It's not so much that we don't
* want to scribble on our input, it's that the parser has a bad habit of
* outputting multiple links to the same subtree for constructs like
* BETWEEN, and we mustn't have OffsetVarNodes increment the varno of a
* Var node twice. copyObject will expand any multiply-referenced subtree
* into multiple copies.
*/
viewParse = copyObject(viewParse);
/* Create a dummy ParseState for addRangeTableEntryForRelation */
pstate = make_parsestate(NULL);
/* need to open the rel for addRangeTableEntryForRelation */
viewRel = relation_open(viewOid, AccessShareLock);
/*
* Create the 2 new range table entries and form the new range table...
* OLD first, then NEW....
*/
nsitem = addRangeTableEntryForRelation(pstate, viewRel,
AccessShareLock,
makeAlias("old", NIL),
false, false);
rt_entry1 = nsitem->p_rte;
nsitem = addRangeTableEntryForRelation(pstate, viewRel,
AccessShareLock,
makeAlias("new", NIL),
false, false);
rt_entry2 = nsitem->p_rte;
/* Must override addRangeTableEntry's default access-check flags */
rt_entry1->requiredPerms = 0;
rt_entry2->requiredPerms = 0;
new_rt = lcons(rt_entry1, lcons(rt_entry2, viewParse->rtable));
viewParse->rtable = new_rt;
/*
* Now offset all var nodes by 2, and jointree RT indexes too.
*/
OffsetVarNodes((Node *) viewParse, 2, 0);
relation_close(viewRel, AccessShareLock);
return viewParse;
}
/*
* DefineView
* Execute a CREATE VIEW command.
*/
ObjectAddress
DefineView(ViewStmt *stmt, const char *queryString,
int stmt_location, int stmt_len)
{
RawStmt *rawstmt;
Query *viewParse;
RangeVar *view;
ListCell *cell;
bool check_option;
ObjectAddress address;
/*
* Run parse analysis to convert the raw parse tree to a Query. Note this
* also acquires sufficient locks on the source table(s).
*
* Since parse analysis scribbles on its input, copy the raw parse tree;
* this ensures we don't corrupt a prepared statement, for example.
*/
rawstmt = makeNode(RawStmt);
rawstmt->stmt = (Node *) copyObject(stmt->query);
rawstmt->stmt_location = stmt_location;
rawstmt->stmt_len = stmt_len;
viewParse = parse_analyze(rawstmt, queryString, NULL, 0, NULL);
/*
* The grammar should ensure that the result is a single SELECT Query.
* However, it doesn't forbid SELECT INTO, so we have to check for that.
*/
if (!IsA(viewParse, Query))
elog(ERROR, "unexpected parse analysis result");
if (viewParse->utilityStmt != NULL &&
IsA(viewParse->utilityStmt, CreateTableAsStmt))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("views must not contain SELECT INTO")));
if (viewParse->commandType != CMD_SELECT)
elog(ERROR, "unexpected parse analysis result");
/*
* Check for unsupported cases. These tests are redundant with ones in
* DefineQueryRewrite(), but that function will complain about a bogus ON
* SELECT rule, and we'd rather the message complain about a view.
*/
if (viewParse->hasModifyingCTE)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("views must not contain data-modifying statements in WITH")));
/*
* If the user specified the WITH CHECK OPTION, add it to the list of
* reloptions.
*/
if (stmt->withCheckOption == LOCAL_CHECK_OPTION)
stmt->options = lappend(stmt->options,
makeDefElem("check_option",
(Node *) makeString("local"), -1));
else if (stmt->withCheckOption == CASCADED_CHECK_OPTION)
stmt->options = lappend(stmt->options,
makeDefElem("check_option",
(Node *) makeString("cascaded"), -1));
/*
* Check that the view is auto-updatable if WITH CHECK OPTION was
* specified.
*/
check_option = false;
foreach(cell, stmt->options)
{
DefElem *defel = (DefElem *) lfirst(cell);
if (strcmp(defel->defname, "check_option") == 0)
check_option = true;
}
/*
* If the check option is specified, look to see if the view is actually
* auto-updatable or not.
*/
if (check_option)
{
const char *view_updatable_error =
view_query_is_auto_updatable(viewParse, true);
if (view_updatable_error)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("WITH CHECK OPTION is supported only on automatically updatable views"),
errhint("%s", _(view_updatable_error))));
}
/*
* If a list of column names was given, run through and insert these into
* the actual query tree. - thomas 2000-03-08
*/
if (stmt->aliases != NIL)
{
ListCell *alist_item = list_head(stmt->aliases);
ListCell *targetList;
foreach(targetList, viewParse->targetList)
{
TargetEntry *te = lfirst_node(TargetEntry, targetList);
/* junk columns don't get aliases */
if (te->resjunk)
continue;
te->resname = pstrdup(strVal(lfirst(alist_item)));
alist_item = lnext(stmt->aliases, alist_item);
if (alist_item == NULL)
break; /* done assigning aliases */
}
if (alist_item != NULL)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("CREATE VIEW specifies more column "
"names than columns")));
}
/* Unlogged views are not sensible. */
if (stmt->view->relpersistence == RELPERSISTENCE_UNLOGGED)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("views cannot be unlogged because they do not have storage")));
/*
* If the user didn't explicitly ask for a temporary view, check whether
* we need one implicitly. We allow TEMP to be inserted automatically as
* long as the CREATE command is consistent with that --- no explicit
* schema name.
*/
view = copyObject(stmt->view); /* don't corrupt original command */
if (view->relpersistence == RELPERSISTENCE_PERMANENT
&& isQueryUsingTempRelation(viewParse))
{
view->relpersistence = RELPERSISTENCE_TEMP;
ereport(NOTICE,
(errmsg("view \"%s\" will be a temporary view",
view->relname)));
}
/*
* Create the view relation
*
* NOTE: if it already exists and replace is false, the xact will be
* aborted.
*/
address = DefineVirtualRelation(view, viewParse->targetList,
stmt->replace, stmt->options, viewParse);
return address;
}
/*
* Use the rules system to store the query for the view.
*/
void
StoreViewQuery(Oid viewOid, Query *viewParse, bool replace)
{
/*
* The range table of 'viewParse' does not contain entries for the "OLD"
* and "NEW" relations. So... add them!
*/
viewParse = UpdateRangeTableOfViewParse(viewOid, viewParse);
/*
* Now create the rules associated with the view.
*/
DefineViewRules(viewOid, viewParse, replace);
}
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