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Generated columns

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This is an SQL-standard feature that allows creating columns that are
computed from expressions rather than assigned, similar to a view or
materialized view but on a column basis.

This implements one kind of generated column: stored (computed on
write).  Another kind, virtual (computed on read), is planned for the
future, and some room is left for it.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/b151f851-4019-bdb1-699e-ebab07d2f40a@2ndquadrant.com
This commit is contained in:
Peter Eisentraut
2019-03-30 08:13:09 +01:00
parent 6b8b5364dd
commit fc22b6623b
84 changed files with 3067 additions and 157 deletions
Download Patch File Download Diff File Expand all files Collapse all files

70
src/backend/parser/parse_utilcmd.c
View File

@ -502,6 +502,7 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
bool saw_nullable;
bool saw_default;
bool saw_identity;
bool saw_generated;
ListCell *clist;
cxt->columns = lappend(cxt->columns, column);
@ -609,6 +610,7 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
saw_nullable = false;
saw_default = false;
saw_identity = false;
saw_generated = false;
foreach(clist, column->constraints)
{
@ -689,6 +691,29 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
break;
}
case CONSTR_GENERATED:
if (cxt->ofType)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("generated columns are not supported on typed tables")));
if (cxt->partbound)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("generated columns are not supported on partitions")));
if (saw_generated)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("multiple generation clauses specified for column \"%s\" of table \"%s\"",
column->colname, cxt->relation->relname),
parser_errposition(cxt->pstate,
constraint->location)));
column->generated = ATTRIBUTE_GENERATED_STORED;
column->raw_default = constraint->raw_expr;
Assert(constraint->cooked_expr == NULL);
saw_generated = true;
break;
case CONSTR_CHECK:
cxt->ckconstraints = lappend(cxt->ckconstraints, constraint);
break;
@ -755,6 +780,22 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
column->colname, cxt->relation->relname),
parser_errposition(cxt->pstate,
constraint->location)));
if (saw_default && saw_generated)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("both default and generation expression specified for column \"%s\" of table \"%s\"",
column->colname, cxt->relation->relname),
parser_errposition(cxt->pstate,
constraint->location)));
if (saw_identity && saw_generated)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("both identity and generation expression specified for column \"%s\" of table \"%s\"",
column->colname, cxt->relation->relname),
parser_errposition(cxt->pstate,
constraint->location)));
}
/*
@ -983,11 +1024,13 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
* Copy default, if present and the default has been requested
*/
if (attribute->atthasdef &&
(table_like_clause->options & CREATE_TABLE_LIKE_DEFAULTS))
(table_like_clause->options & CREATE_TABLE_LIKE_DEFAULTS ||
table_like_clause->options & CREATE_TABLE_LIKE_GENERATED))
{
Node *this_default = NULL;
AttrDefault *attrdef;
int i;
bool found_whole_row;
/* Find default in constraint structure */
Assert(constr != NULL);
@ -1002,12 +1045,27 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
}
Assert(this_default != NULL);
/*
* If default expr could contain any vars, we'd need to fix 'em,
* but it can't; so default is ready to apply to child.
*/
def->cooked_default = map_variable_attnos(this_default,
1, 0,
attmap, tupleDesc->natts,
InvalidOid, &found_whole_row);
def->cooked_default = this_default;
/*
* Prevent this for the same reason as for constraints below.
* Note that defaults cannot contain any vars, so it's OK that the
* error message refers to generated columns.
*/
if (found_whole_row)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot convert whole-row table reference"),
errdetail("Generation expression for column \"%s\" contains a whole-row reference to table \"%s\".",
attributeName,
RelationGetRelationName(relation))));
if (attribute->attgenerated &&
(table_like_clause->options & CREATE_TABLE_LIKE_GENERATED))
def->generated = attribute->attgenerated;
}
/*