Optional blocks can also be nested, in which case the inner optional block is only considered when the outer optional block's pattern matches the graph.
可选块也可以嵌套,在这种情况下,只有外部可选块的模式与图形匹配时,才考虑内部可选块。
2
When an error occurs within a nested TRY block, program control is transferred to the CATCH block that is associated with the nested TRY block.
当嵌套的TRY块中出现错误时,程序控制将传递到与嵌套的TRY块关联的CATCH块。
3
In order to solve the difficulty of nested structure of SQL, the idea of query block is introduced and the algorithm of changing query block to SQL is realized.