UPDATE

功能描述

更新表中的数据。UPDATE修改满足条件的所有行中指定的字段值，WHERE子句声明条件，SET子句指定的字段会被修改，没有出现的字段则保持它们的原值。

注意事项

• 本章节仅包含shark新增语法，原openGauss的UPDATE语法未作删除和修改。原openGauss的UPDATE语法请参考章节UPDATE。
• 新增支持table_hint子句。

语法格式

单表更新：
[ WITH [ RECURSIVE ] with_query [, ...] ]
UPDATE [/*+ plan_hint */] [ ONLY ] table_name [ partition_clause ] [ * ] [ [ AS ] alias ] [table_hint_clause]
SET {column_name = { expression | DEFAULT } 
    |( column_name [, ...] ) = {( { expression | DEFAULT } [, ...] ) |sub_query }}[, ...]
    [ FROM from_list] [JOIN join_table ON join_condition]... ]
    [ WHERE condition | WHERE CURRENT OF cursor_name ]
    [ ORDER BY {expression [ [ ASC | DESC | USING operator ]
    [ LIMIT { count } ]
    [ RETURNING {* 
                | {output_expression [ [ AS ] output_name ]} [, ...] }];

多表更新：
[ WITH [ RECURSIVE ] with_query [, ...] ]
UPDATE [/*+ plan_hint */] table_list
SET {column_name = { expression | DEFAULT } 
    |( column_name [, ...] ) = {( { expression | DEFAULT } [, ...] ) |sub_query }}[, ...]
    [ FROM from_list] [ WHERE condition ];

where sub_query can be:
SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
{ * | {expression [ [ AS ] output_name ]} [, ...] }
[ FROM from_item [, ...] ] [JOIN join_table ON join_condition]... ]
[ WHERE condition ]
[ GROUP BY grouping_element [, ...] ]
[ HAVING condition [, ...] ]
[ ORDER BY {expression [ [ ASC | DESC | USING operator ] | nlssort_expression_clause ] [ NULLS { FIRST | LAST } ]} [, ...] ]
[ LIMIT { [offset,] count | ALL } ]

• 其中table_hint子句table_hint_clause为：

  WITH ( <table_hint> [, ...] ) 
  

参数说明

• JOIN

  JOIN包含 INNER JOIN，LEFT JOIN，RIGHT JOIN，FULL JOIN，CROSS JOIN。

• WITH ( <table_hint> [, …] )

  • 不同于SELECT子句，针对单个hint，WITH可选，针对UPDATE子句，WITH必选，table_hint支持给出一个列表选项，列表通过逗号或者空格分隔，即WITH (hint1)、WITH (hint1, hint2, …)、WITH (hint1 hint2 …)均支持，(hint1)不支持。

  • 支持的hint包括NOLOCK、READUNCOMMITTED、UPDLOCK、REPEATABLEREAD、SERIALIZABLE、READCOMMITTED、TABLOCK、TABLOCKX、PAGLOCK、ROWLOCK、NOWAIT、READPAST、XLOCK、SNAPSHOT、NOEXPAND。

  • 当上述hint需要当做标识符，用于列名、变量名等，需要设置d_format_behavior_compat_options = 'enable_table_hint_identifier'，该变量默认值d_format_behavior_compat_options = ''。

  • 所有的hint仅语法支持，无实际含义。

  • 针对hint，会打印相关NOTICE信息。

table_hint子句示例

create table t1(c1 int);

update t1 with (xlock) set c1 = 10 where c1 = 5;
NOTICE:  The xlock option is currently ignored

update t1 with (xlock, nowait) set c1 = 3 where c1 = 10;
NOTICE:  The xlock option is currently ignored
NOTICE:  The nowait option is currently ignored

update t1 as alias_t1 with (xlock) set c1 = 20 where c1 = 2;
NOTICE:  The xlock option is currently ignored

update t1 as alias_t1 with (xlock, nowait) set c1 = 20 where c1 = 2;
NOTICE:  The xlock option is currently ignored
NOTICE:  The nowait option is currently ignored

update t1 as alias_t1 with (xlock nowait) set c1 = 20 where c1 = 2;
NOTICE:  The xlock option is currently ignored
NOTICE:  The nowait option is currently ignored

相关链接

UPDATE