Function EvalAsOfTimestamp

pkg/sql/sem/tree/as_of.go:37–83

EvalAsOfTimestamp evaluates the timestamp argument to an AS OF SYSTEM TIME query.

(
	asOf AsOfClause, semaCtx *SemaContext, evalCtx *EvalContext,
)

// EvalAsOfTimestamp evaluates the timestamp argument to an AS OF SYSTEM TIME query.
func EvalAsOfTimestamp(
	asOf AsOfClause, semaCtx *SemaContext, evalCtx *EvalContext,
) (tsss hlc.Timestamp, err error) {
	// We need to save and restore the previous value of the field in
	// semaCtx in case we are recursively called within a subquery
	// context.
	scalarProps := &semaCtx.Properties
	defer scalarProps.Restore(*scalarProps)
	scalarProps.Require("AS OF SYSTEM TIME", RejectSpecial|RejectSubqueries)

	// In order to support the follower reads feature we permit this expression
	// to be a simple invocation of the `FollowerReadTimestampFunction`.
	// Over time we could expand the set of allowed functions or expressions.
	// All non-function expressions must be const and must TypeCheck into a
	// string.
	var te TypedExpr
	if fe, ok := asOf.Expr.(*FuncExpr); ok {
		def, err := fe.Func.Resolve(semaCtx.SearchPath)
		if err != nil {
			return hlc.Timestamp{}, errInvalidExprForAsOf
		}
		if def.Name != FollowerReadTimestampFunctionName {
			return hlc.Timestamp{}, errInvalidExprForAsOf
		}
		if te, err = fe.TypeCheck(semaCtx, types.TimestampTZ); err != nil {
			return hlc.Timestamp{}, err
		}
	} else {
		var err error
		te, err = asOf.Expr.TypeCheck(semaCtx, types.String)
		if err != nil {
			return hlc.Timestamp{}, err
		}
		if !IsConst(evalCtx, te) {
			return hlc.Timestamp{}, errInvalidExprForAsOf
		}
	}

	d, err := te.Eval(evalCtx)
	if err != nil {
		return hlc.Timestamp{}, err
	}

	stmtTimestamp := evalCtx.GetStmtTimestamp()
	ts, err := DatumToHLC(evalCtx, stmtTimestamp, d)
	return ts, errors.Wrap(err, "AS OF SYSTEM TIME")
}

// DatumToHLC performs the conversion from a Datum to an HLC timestamp.
func DatumToHLC(evalCtx *EvalContext, stmtTimestamp time.Time, d Datum) (hlc.Timestamp, error) {