. . . . . . . . . . . . . . . . . . . . . . 295 7.9 In SQLSever and PostgreSQL, why does the aggregation column without alias throw ex‐ ception? . . . . . . . . . . . . . . . . . . . . . . . . . . . name after sharding, or misconducts caused by operations such as pagination, order by or aggregated group by are just the case in point. 3.1. Sharding 10 Apache ShardingSphere document, v5.0.0-beta Cross‐database extract the parsing context, which can include tables, options, ordering items, grouping items, aggregation functions, pagination information, query conditions and placeholders that may be revised. Query

. . . . . . . . . . . . . . . . . . . . . . 257 Group‐by Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Aggregation Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 7.7.20 20. [Other] In SQLSever and PostgreSQL, why does the aggregation column with‐ out alias throw exception? . . . . . . . . . . . . . . . . . . . . . . . . . . . t_order CHECK TABLE t_order SET RESOURCE GROUP group_name DROP RESOURCE GROUP group_name CREATE RESOURCE GROUP group_name TYPE = SYSTEM ALTER RESOURCE GROUP rg1 VCPU = 0‐63 4.1. DB Compatibility 19

. . . . . . . . . . . . . . . . . . . . . . 267 Group‐by Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Aggregation Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 7.8.23 [Other] In SQLSever and PostgreSQL, why does the aggregation column without alias throw exception? . . . . . . . . . . . . . . . . . . . . . . . . . . . . t_order CHECK TABLE t_order SET RESOURCE GROUP group_name DROP RESOURCE GROUP group_name CREATE RESOURCE GROUP group_name TYPE = SYSTEM ALTER RESOURCE GROUP rg1 VCPU = 0‐63 openGauss The unsupported

. . . . . . . . . . . . . . . . . . . . . . 278 Group‐by Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Aggregation Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 7.8.23 [Other] In SQLSever and PostgreSQL, why does the aggregation column without alias throw exception? . . . . . . . . . . . . . . . . . . . . . . . . . . . . t_order CHECK TABLE t_order SET RESOURCE GROUP group_name DROP RESOURCE GROUP group_name CREATE RESOURCE GROUP group_name TYPE = SYSTEM ALTER RESOURCE GROUP rg1 VCPU = 0‐63 Source Codes: https://github

. . . . . . . . . . . . . . . . . . . . . . 382 Group‐by Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384 Aggregation Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461 8.6.3 Other In SQLSever and PostgreSQL, why does the aggregation column without alias throw exception? . . . . . . . . . . . . . . . . . . . . . . . . . . . . try to reduce the influence of sharding, in order to let users use horizontal sharding database group like one database. 3.1.4 Application Scenarios Mass data high concurrency in OLTP scenarios Most

. . . . . . . . . . . . . . . . . . . . . . 409 Group‐by Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 Aggregation Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 8.6.3 Other In SQLSever and PostgreSQL, why does the aggregation column without alias throw exception? . . . . . . . . . . . . . . . . . . . . . . . . . . . . provides complex data query and analysis capabilities across data sources, simpli‐ fying the data aggregation from different data locations. Data En‐ cryp‐ tion Data Encryption is a basic way to ensure

. . . . . . . . . . . . . . . . . . . . . . 550 Group‐by Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 Aggregation Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582 13.6.3 Other In SQLSever and PostgreSQL, why does the aggregation column without alias throw exception? . . . . . . . . . . . . . . . . . . . . . . . . . . . . provides complex data query and analysis capabilities across data sources, simpli‐ fying the data aggregation from different data locations. Da ta En cr yp ti on Data Encryption is a basic way to ensure

. . . . . . . . . . . . . . . . . . . . . . 521 Group‐by Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523 Aggregation Merger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 xii 13.6.3 Other In SQLSever and PostgreSQL, why does the aggregation column without alias throw exception? . . . . . . . . . . . . . . . . . . . . . . . . . . . . provides complex data query and analysis capabilities across data sources, simpli‐ fying the data aggregation from different data locations. Da ta En cr yp ti on Data Encryption is a basic way to ensure

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Items）、表信 息（Table）、分片条件（Sharding Condition）、自增主键信息（Auto increment Primary Key）、排序信 息（Order By）、分组信息（Group By）以及分页信息（Limit、Rownum、Top）。SQL 的一次解析过程 是不可逆的，一个个 Token 按 SQL 原本的顺序依次进行解析，性能很高。考虑到各种数据库 SQL 方言的 需要在查询语句中补列通常由两种情况导致。第一种情况是 ShardingSphere 需要在结果归并时获取相应 数据，但该数据并未能通过查询的 SQL 返回。这种情况主要是针对 GROUP BY 和 ORDER BY。结果归并 时，需要根据 GROUP BY 和 ORDER BY 的字段项进行分组和排序，但如果原始 SQL 的选择项中若并未包 含分组项或排序项，则需要对原始 SQL 进行改写。先看一下原始 SQL 则无需涉及到结果归并。因此补列和分页信息等改写都没有必要进行。尤其是分页信息的改写，无需将 数据从第 1 条开始取，大量的降低了对数据库的压力，并且节省了网络带宽的无谓消耗。 流式归并优化 它仅为包含 GROUP BY 的 SQL 增加 ORDER BY 以及和分组项相同的排序项和排序顺序，用于将内存归 并转化为流式归并。在结果归并的部分中，将对流式归并和内存归并进行详细说明。 改写引擎的整体结构划分如下图所示。