Function transformPartitionBoundValue

src/backend/parser/parse_utilcmd.c:5526–5595

* Transform one entry in a partition bound spec, producing a constant. */

 * Transform one entry in a partition bound spec, producing a constant.
 */
Const *
transformPartitionBoundValue(ParseState *pstate, Node *val,
							 const char *colName, Oid colType, int32 colTypmod,
							 Oid partCollation)
{
	Node	   *value;

	/* Transform raw parsetree */
	value = transformExpr(pstate, val, EXPR_KIND_PARTITION_BOUND);

	/*
	 * transformExpr() should have already rejected column references,
	 * subqueries, aggregates, window functions, and SRFs, based on the
	 * EXPR_KIND_ of a partition bound expression.
	 */
	Assert(!contain_var_clause(value));

	/*
	 * Coerce to the correct type.  This might cause an explicit coercion step
	 * to be added on top of the expression, which must be evaluated before
	 * returning the result to the caller.
	 */
	value = coerce_to_target_type(pstate,
								  value, exprType(value),
								  colType,
								  colTypmod,
								  COERCION_ASSIGNMENT,
								  COERCE_IMPLICIT_CAST,
								  -1);

	if (value == NULL)
		ereport(ERROR,
				(errcode(ERRCODE_DATATYPE_MISMATCH),
				 errmsg("specified value cannot be cast to type %s for column \"%s\"",
						format_type_be(colType), colName),
				 parser_errposition(pstate, exprLocation(val))));

	/*
	 * Evaluate the expression, if needed, assigning the partition key's data
	 * type and collation to the resulting Const node.
	 */
	if (!IsA(value, Const))
	{
		assign_expr_collations(pstate, value);
		value = (Node *) expression_planner((Expr *) value);
		value = (Node *) evaluate_expr((Expr *) value, colType, colTypmod,
									   partCollation);
		if (!IsA(value, Const))
			elog(ERROR, "could not evaluate partition bound expression");
	}
	else
	{
		/*
		 * If the expression is already a Const, as is often the case, we can
		 * skip the rather expensive steps above.  But we still have to insert
		 * the right collation, since coerce_to_target_type doesn't handle
		 * that.
		 */