云数据库 GAUSSDB-SELECT:语法格式

时间:2024-12-19 14:11:11

语法格式

  • 查询数据
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[ WITH [ RECURSIVE ] with_query [, ...] ]
SELECT [/*+ plan_hint */] [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
    { * | {expression [ [ AS ] output_name ]} [, ...] }
    [ FROM from_item [, ...] ]
    [ WHERE condition ]
    [ GROUP BY grouping_element [, ...] ]
    [ HAVING condition [, ...] ]
    [ WINDOW {window_name AS ( window_definition )} [, ...] ]
    [ { UNION | INTERSECT | EXCEPT | MINUS } [ ALL | DISTINCT ] select ]
    [ ORDER BY {expression [ [ ASC | DESC | USING operator ] | nlssort_expression_clause ] [ NULLS { FIRST | LAST } ]} [, ...] ]
    [ LIMIT { [offset,] count | ALL } ]
    [ OFFSET start [ ROW | ROWS ] ]
    [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ]
    [ {FOR { UPDATE | SHARE } [ OF table_name [, ...] ] [ NOWAIT | WAIT n]} [...] ]
    TABLE { ONLY { (table_name) | table_name } | table_name [ * ]};

condition和expression中可以使用targetlist中表达式的别名。

  • 只能同一层引用。
  • 只能引用targetlist中的别名。
  • 只能是后面的表达式引用前面的表达式。
  • 不能包含volatile函数。
  • 不能包含Window function函数。
  • 不支持在JOIN ON条件中引用别名。
  • targetlist中有多个要应用的别名则报错。
  • 其中子查询with_query为:
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    with_query_name [ ( column_name [, ...] ) ]
        AS [ [ NOT ] MATERIALIZED ] ( {select | values | insert | update | delete} )
    
  • 其中指定查询源from_item为:
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    {[ ONLY ] table_name [ * ] [ partition_clause ] [ [ AS ] alias [ ( column_alias [, ...] ) ] ]
    [ TABLESAMPLE sampling_method ( argument [, ...] ) [ REPEATABLE ( seed ) ] ]
    |( select ) [ AS ] alias [ ( column_alias [, ...] ) ]
    |with_query_name [ [ AS ] alias [ ( column_alias [, ...] ) ] ]
    |function_name ( [ argument [, ...] ] ) [ AS ] alias [ ( column_alias [, ...] | column_definition [, ...] ) ]
    |function_name ( [ argument [, ...] ] ) AS ( column_definition [, ...] )
    |from_item [ NATURAL ] join_type from_item [ ON join_condition | USING ( join_column [, ...] ) ]}
    
  • 其中group子句为:
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    ( )
    | expression
    | ( expression [, ...] )
    | ROLLUP ( { expression | ( expression [, ...] ) } [, ...] )
    | CUBE ( { expression | ( expression [, ...] ) } [, ...] )
    | GROUPING SETS ( grouping_element [, ...] )
    
  • from_item中指定分区partition_clause为:
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    PARTITION { ( partition_name ) | 
            FOR (  partition_value [, ...] ) }
    

    指定分区只适合分区表。

  • 其中设置排序方式nlssort_expression_clause为:
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    NLSSORT ( column_name, ' NLS_SORT = { SCHINESE_PINYIN_M | generic_m_ci } ' )
    

    第二个参数可选generic_m_ci,仅支持纯英文不区分大小写排序。

  • 简化版查询语法,功能相当于SELECT * FROM table_name。
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    TABLE { ONLY {(table_name)| table_name} | table_name [ * ]};
    
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