DELETE 算子用于刪除數(shù)據(jù)表中滿足指定條件的數(shù)據(jù)行。

我們是從2013年成立的成都網(wǎng)站建設(shè)公司,提供網(wǎng)站建設(shè),電商網(wǎng)站設(shè)計(jì)開發(fā),外貿(mào)網(wǎng)站建設(shè),響應(yīng)式網(wǎng)頁設(shè)計(jì),微信平臺(tái)小程序開發(fā)、等服務(wù)。為客戶創(chuàng)造有價(jià)值的品牌營銷體驗(yàn)，讓互聯(lián)網(wǎng)提升企業(yè)的競爭力！

OceanBase 數(shù)據(jù)庫支持的 DELETE 算子包括 DELETE 和 MULTI PARTITION DELETE。

DELETE

DELETE 算子用于刪除數(shù)據(jù)表單個(gè)分區(qū)中的數(shù)據(jù)。

如下例所示，Q1 查詢刪除了表 t1 中所有滿足 c2>'100' 的行。

obclient>CREATE TABLE t1 (c1 INT PRIMARY KEY, c2 VARCHAR2(10));
Query OK, 0 rows affected (0.12 sec)

obclient>CREATE TABLE t2 (c1 INT PRIMARY KEY, c2 VARCHAR2(10)) PARTITION BY 
             HASH(c1) PARTITIONS 10;
Query OK, 0 rows affected (0.12 sec)

obclient>CREATE TABLE t3 (c1 INT PRIMARY KEY, c2 VARCHAR2(10));
Query OK, 0 rows affected (0.12 sec)

obclient>CREATE INDEX IDX_t3_c2 ON t3 (c2) PARTITION BY HASH(c2) PARTITIONS 3;
Query OK, 0 rows affected (0.12 sec)

Q1: 
obclient>EXPLAIN DELETE FROM t1 WHERE c2 > '100'\G;
*************************** 1. row ***************************
Query Plan:
======================================
|ID|OPERATOR   |NAME|EST. ROWS|COST  |
--------------------------------------
|0 |DELETE     |    |10000    |118697|
|1 | TABLE SCAN|T1  |10000    |108697|
======================================

Outputs & filters:
-------------------------------------
  0 - output(nil), filter(nil), table_columns([{T1: ({T1: (T1.C1, T1.C2)})}])
  1 - output([T1.C1], [T1.C2]), filter([T1.C2 > '100']),
      access([T1.C1], [T1.C2]), partitions(p0)

上述示例中，執(zhí)行計(jì)劃展示中的 outputs & filters 詳細(xì)列出了 DELETE 算子的輸出信息如下：

信息名稱	含義
output	該算子輸出的表達(dá)式。
filter	該算子上的過濾條件。由于示例中 DELETE 算子沒有設(shè)置 filter，所以為 nil。對(duì)于刪除語句，WHERE 中的謂詞會(huì)下推到基表上，比如 Q1 查詢中的 c2>'100' 被下推到了 1 號(hào)算子上。
table_columns	刪除操作涉及的數(shù)據(jù)表的列。

更多 DELETE 算子的示例如下：

• Q2 查詢刪除 t1 中的所有數(shù)據(jù)行。

• Q3 查詢刪除分區(qū)表 t2 中滿足 c1 = 1 的數(shù)據(jù)行。

• Q4 查詢刪除分區(qū)表 t2 中滿足 c2 > '100'  的數(shù)據(jù)行。從執(zhí)行計(jì)劃中可以看到，DELETE 算子分配在 EXCHANGE 算子下面，因此 2 號(hào)和 3 號(hào)算子會(huì)作為一個(gè) task 以分區(qū)的粒度進(jìn)行調(diào)度。在計(jì)劃執(zhí)行時(shí)， 3 號(hào)算子掃描出 t2 一個(gè)分區(qū)中滿足 c2 > '100' 的數(shù)據(jù)，2 號(hào)算子 DELETE 則只會(huì)刪除相應(yīng)分區(qū)下掃描出的數(shù)據(jù)。

Q2: 
obclient>EXPLAIN DELETE FROM t1\G;
*************************** 1. row ***************************
Query Plan:
======================================
|ID|OPERATOR   |NAME|EST. ROWS|COST  |
--------------------------------------
|0 |DELETE     |    |100000   |161860|
|1 | TABLE SCAN|T1  |100000   |61860 |
======================================

Outputs & filters:
-------------------------------------
  0 - output(nil), filter(nil), table_columns([{T1: ({T1: (T1.C1, T1.C2)})}])
  1 - output([T1.C1], [T1.C2]), filter(nil),
      access([T1.C1], [T1.C2]), partitions(p0)
 

Q3: 
obclient>EXPLAIN DELETE FROM t2 WHERE c1 = 1\G;
*************************** 1. row ***************************
Query Plan:
===================================
|ID|OPERATOR  |NAME|EST. ROWS|COST|
-----------------------------------
|0 |DELETE    |    |1        |53  |
|1 | TABLE GET|T2  |1        |52  |
===================================

Outputs & filters:
-------------------------------------
  0 - output(nil), filter(nil), table_columns([{T2: ({T2: (T2.C1, T2.C2)})}])
  1 - output([T2.C1], [T2.C2]), filter(nil),
      access([T2.C1], [T2.C2]), partitions(p5) 
 

Q4: 
obclient>EXPLAIN DELETE FROM t2 WHERE c2 > '100'\G;
*************************** 1. row ***************************
Query Plan:
===============================================

|ID|OPERATOR               |NAME    |EST. ROWS|COST   |
-------------------------------------------------------
|0 |PX COORDINATOR         |        |100000   |1186893|
|1 | EXCHANGE OUT DISTR    |:EX10000|100000   |1186893|
|2 |  PX PARTITION ITERATOR|        |100000   |1186893|
|3 |   DELETE              |        |100000   |1186893|
|4 |    TABLE SCAN         |T2      |100000   |1086893|
==================================================

Outputs & filters:
-------------------------------------
  0 - output(nil), filter(nil)
  1 - output(nil), filter(nil), dop=1
  2 - output(nil), filter(nil)
  3 - output(nil), filter(nil), table_columns([{T2: ({T2: (T2.C1, T2.C2)})}])
  4 - output([T2.C1], [T2.C2]), filter([T2.C2 > '100']),
      access([T2.C1], [T2.C2]), partitions(p[0-9])

MULTI PARTITION DELETE

MULTI PARTITION DELETE 算子用于刪除數(shù)據(jù)表多個(gè)分區(qū)中的數(shù)據(jù)。

如下例所示，Q5 查詢刪除了表 t3 中所有滿足 c2 > '100'  的數(shù)據(jù)行。雖然 t3 本身是一個(gè)非分區(qū)表，但因?yàn)?t3 上存在全局索引 idx_t3_c2，因此每一條數(shù)據(jù)行會(huì)存在于多個(gè)分區(qū)中。

Q5: 
obclient>EXPLAIN DELETE FROM t3 WHERE c2 > '100'\G;
*************************** 1. row ***************************
Query Plan:
========================================================

|ID|OPERATOR                |NAME         |EST. ROWS|COST |
-----------------------------------------------------------
|0 |MULTI PARTITION DELETE  |             |10001    |27780|
|1 | PX COORDINATOR         |             |10001    |17780|
|2 |  EXCHANGE OUT DISTR    |:EX10000     |10001    |14941|
|3 |   PX PARTITION ITERATOR|             |10001    |14941|
|4 |    TABLE SCAN          |T3(IDX_T3_C2)|10001    |14941|
===========================================================

Outputs & filters:
-------------------------------------
  0 - output(nil), filter(nil), table_columns([{T3: ({T3: (T3.C1, T3.C2)}, {IDX_T3_C2: (T3.C2, T3.C1)})}])
  1 - output([T3.C1], [T3.C2]), filter(nil)
  2 - output([T3.C2], [T3.C1]), filter(nil), dop=1
  3 - output([T3.C2], [T3.C1]), filter(nil)
  4 - output([T3.C2], [T3.C1]), filter(nil),
      access([T3.C2], [T3.C1]), partitions(p[0-2])

上述示例的執(zhí)行計(jì)劃展示中的 outputs & filters 詳細(xì)列出了 MULTI PARTITION DELETE 算子的信息，字段的含義與 DELETE 算子相同。

名稱欄目：創(chuàng)新互聯(lián)OceanBase教程：OceanBaseDELETE
標(biāo)題路徑：http://uogjgqi.cn/article/coijpce.html