func makeDefaultExprs(
	cols []sqlbase.ColumnDescriptor, parse *parser.Parser, evalCtx *parser.EvalContext,
) ([]parser.TypedExpr, error) {
	// Check to see if any of the columns have DEFAULT expressions. If there
	// are no DEFAULT expressions, we don't bother with constructing the
	// defaults map as the defaults are all NULL.
	haveDefaults := false
	for _, col := range cols {
		if col.DefaultExpr != nil {
			haveDefaults = true
			break
		}
	}
	if !haveDefaults {
		return nil, nil
	}

	// Build the default expressions map from the parsed SELECT statement.
	defaultExprs := make([]parser.TypedExpr, 0, len(cols))
	exprStrings := make([]string, 0, len(cols))
	for _, col := range cols {
		if col.DefaultExpr != nil {
			exprStrings = append(exprStrings, *col.DefaultExpr)
		}
	}
	exprs, err := parser.ParseExprsTraditional(exprStrings)
	if err != nil {
		return nil, err
	}

	defExprIdx := 0
	for _, col := range cols {
		if col.DefaultExpr == nil {
			defaultExprs = append(defaultExprs, parser.DNull)
			continue
		}
		expr := exprs[defExprIdx]
		typedExpr, err := parser.TypeCheck(expr, nil, col.Type.ToDatumType())
		if err != nil {
			return nil, err
		}
		if typedExpr, err = parse.NormalizeExpr(evalCtx, typedExpr); err != nil {
			return nil, err
		}
		defaultExprs = append(defaultExprs, typedExpr)
		defExprIdx++
	}
	return defaultExprs, nil
}

func makeDefaultExprs(
	cols []ColumnDescriptor, parse *parser.Parser, evalCtx parser.EvalContext,
) ([]parser.Expr, error) {
	// Check to see if any of the columns have DEFAULT expressions. If there
	// are no DEFAULT expressions, we don't bother with constructing the
	// defaults map as the defaults are all NULL.
	haveDefaults := false
	for _, col := range cols {
		if col.DefaultExpr != nil {
			haveDefaults = true
			break
		}
	}
	if !haveDefaults {
		return nil, nil
	}

	// Build the default expressions map from the parsed SELECT statement.
	defaultExprs := make([]parser.Expr, 0, len(cols))
	for _, col := range cols {
		if col.DefaultExpr == nil {
			defaultExprs = append(defaultExprs, parser.DNull)
			continue
		}
		expr, err := parser.ParseExprTraditional(*col.DefaultExpr)
		if err != nil {
			return nil, err
		}
		expr, err = parse.NormalizeExpr(evalCtx, expr)
		if err != nil {
			return nil, err
		}
		if parser.ContainsVars(expr) {
			return nil, util.Errorf("default expression contains variables")
		}
		defaultExprs = append(defaultExprs, expr)
	}
	return defaultExprs, nil
}

// MakeColumnDefDescs creates the column descriptor for a column, as well as the
// index descriptor if the column is a primary key or unique.
func MakeColumnDefDescs(d *parser.ColumnTableDef) (*ColumnDescriptor, *IndexDescriptor, error) {
	col := &ColumnDescriptor{
		Name:     string(d.Name),
		Nullable: d.Nullable.Nullability != parser.NotNull && !d.PrimaryKey,
	}

	if d.Nullable.ConstraintName != "" {
		col.NullableConstraintName = string(d.Nullable.ConstraintName)
	}

	var colDatumType parser.Datum
	switch t := d.Type.(type) {
	case *parser.BoolColType:
		col.Type.Kind = ColumnType_BOOL
		colDatumType = parser.TypeBool
	case *parser.IntColType:
		col.Type.Kind = ColumnType_INT
		col.Type.Width = int32(t.N)
		colDatumType = parser.TypeInt
		if t.IsSerial() {
			if d.DefaultExpr.Expr != nil {
				return nil, nil, fmt.Errorf("SERIAL column %q cannot have a default value", col.Name)
			}
			s := "unique_rowid()"
			col.DefaultExpr = &s
		}
	case *parser.FloatColType:
		col.Type.Kind = ColumnType_FLOAT
		col.Type.Precision = int32(t.Prec)
		colDatumType = parser.TypeFloat
	case *parser.DecimalColType:
		col.Type.Kind = ColumnType_DECIMAL
		col.Type.Width = int32(t.Scale)
		col.Type.Precision = int32(t.Prec)
		colDatumType = parser.TypeDecimal
	case *parser.DateColType:
		col.Type.Kind = ColumnType_DATE
		colDatumType = parser.TypeDate
	case *parser.TimestampColType:
		col.Type.Kind = ColumnType_TIMESTAMP
		colDatumType = parser.TypeTimestamp
	case *parser.TimestampTZColType:
		col.Type.Kind = ColumnType_TIMESTAMPTZ
		colDatumType = parser.TypeTimestampTZ
	case *parser.IntervalColType:
		col.Type.Kind = ColumnType_INTERVAL
		colDatumType = parser.TypeInterval
	case *parser.StringColType:
		col.Type.Kind = ColumnType_STRING
		col.Type.Width = int32(t.N)
		colDatumType = parser.TypeString
	case *parser.BytesColType:
		col.Type.Kind = ColumnType_BYTES
		colDatumType = parser.TypeBytes
	default:
		return nil, nil, errors.Errorf("unexpected type %T", t)
	}

	if col.Type.Kind == ColumnType_DECIMAL {
		switch {
		case col.Type.Precision == 0 && col.Type.Width > 0:
			// TODO (seif): Find right range for error message.
			return nil, nil, errors.New("invalid NUMERIC precision 0")
		case col.Type.Precision < col.Type.Width:
			return nil, nil, fmt.Errorf("NUMERIC scale %d must be between 0 and precision %d",
				col.Type.Width, col.Type.Precision)
		}
	}

	if d.DefaultExpr.Expr != nil {
		// Verify the default expression type is compatible with the column type.
		if err := SanitizeVarFreeExpr(d.DefaultExpr.Expr, colDatumType, "DEFAULT"); err != nil {
			return nil, nil, err
		}
		var p parser.Parser
		if p.AggregateInExpr(d.DefaultExpr.Expr) {
			return nil, nil, fmt.Errorf("Aggregate functions are not allowed in DEFAULT expressions")
		}
		if d.DefaultExpr.ConstraintName != "" {
			col.DefaultExprConstraintName = string(d.DefaultExpr.ConstraintName)
		}
		s := d.DefaultExpr.Expr.String()
		col.DefaultExpr = &s
	}

	var idx *IndexDescriptor
	if d.PrimaryKey || d.Unique {
		idx = &IndexDescriptor{
			Unique:           true,
			ColumnNames:      []string{string(d.Name)},
			ColumnDirections: []IndexDescriptor_Direction{IndexDescriptor_ASC},
		}
		if d.UniqueConstraintName != "" {
			idx.Name = string(d.UniqueConstraintName)
		}
	}

	return col, idx, nil
//.........这里部分代码省略.........