Function nodeExplain

server/ast/explain.go:26–73

nodeExplain handles *tree.Explain nodes.

(ctx *Context, node *tree.Explain)

// nodeExplain handles *tree.Explain nodes.
func nodeExplain(ctx *Context, node *tree.Explain) (vitess.Statement, error) {
	if node == nil {
		return nil, nil
	}

	if node.TableName != nil {
		tableName, err := nodeUnresolvedObjectName(ctx, node.TableName)
		if err != nil {
			return nil, err
		}

		var showTableOpts *vitess.ShowTablesOpt
		if node.AsOf != nil {
			asOf, err := nodeExpr(ctx, node.AsOf.Expr)
			if err != nil {
				return nil, err
			}
			showTableOpts = &vitess.ShowTablesOpt{
				AsOf:       asOf,
				SchemaName: tableName.SchemaQualifier.String(),
				DbName:     tableName.DbQualifier.String(),
			}
		}

		show := &vitess.Show{
			Type:          "columns",
			Table:         tableName,
			ShowTablesOpt: showTableOpts,
		}

		return show, nil
	}

	if stmt, ok := node.Statement.(*tree.Select); ok {
		// TODO: read tree.ExplainOptions
		selectStmt, err := nodeSelect(ctx, stmt)
		if err != nil {
			return nil, err
		}
		explain := &vitess.Explain{
			ExplainFormat: vitess.TreeStr,
			Statement:     selectStmt,
		}
		return explain, nil
	}

	return nil, errors.Errorf("This EXPLAIN syntax is not yet supported")
}