Hive 表定义主键约束

文章目录

1.建表语句
2.主键约束
3.主键约束的意义
参考文献

1.建表语句

先看一下官方给的完整的见表语句：

CREATE [TEMPORARY] [EXTERNAL] TABLE [IF NOT EXISTS] [db_name.]table_name    -- (Note: TEMPORARY available in Hive 0.14.0 and later)[(col_name data_type [column_constraint_specification] [COMMENT col_comment], ... [constraint_specification])][COMMENT table_comment][PARTITIONED BY (col_name data_type [COMMENT col_comment], ...)][CLUSTERED BY (col_name, col_name, ...) [SORTED BY (col_name [ASC|DESC], ...)] INTO num_buckets BUCKETS][SKEWED BY (col_name, col_name, ...)                  -- (Note: Available in Hive 0.10.0 and later)]ON ((col_value, col_value, ...), (col_value, col_value, ...), ...)[STORED AS DIRECTORIES][[ROW FORMAT row_format] [STORED AS file_format]| STORED BY 'storage.handler.class.name' [WITH SERDEPROPERTIES (...)]  -- (Note: Available in Hive 0.6.0 and later)][LOCATION hdfs_path][TBLPROPERTIES (property_name=property_value, ...)]   -- (Note: Available in Hive 0.6.0 and later)[AS select_statement];   -- (Note: Available in Hive 0.5.0 and later; not supported for external tables)CREATE [TEMPORARY] [EXTERNAL] TABLE [IF NOT EXISTS] [db_name.]table_nameLIKE existing_table_or_view_name[LOCATION hdfs_path];data_type: primitive_type| array_type| map_type| struct_type| union_type  -- (Note: Available in Hive 0.7.0 and later)primitive_type: TINYINT| SMALLINT| INT| BIGINT| BOOLEAN| FLOAT| DOUBLE| DOUBLE PRECISION -- (Note: Available in Hive 2.2.0 and later)| STRING| BINARY      -- (Note: Available in Hive 0.8.0 and later)| TIMESTAMP   -- (Note: Available in Hive 0.8.0 and later)| DECIMAL     -- (Note: Available in Hive 0.11.0 and later)| DECIMAL(precision, scale)  -- (Note: Available in Hive 0.13.0 and later)| DATE        -- (Note: Available in Hive 0.12.0 and later)| VARCHAR     -- (Note: Available in Hive 0.12.0 and later)| CHAR        -- (Note: Available in Hive 0.13.0 and later)array_type: ARRAY < data_type >map_type: MAP < primitive_type, data_type >struct_type: STRUCT < col_name : data_type [COMMENT col_comment], ...>union_type: UNIONTYPE < data_type, data_type, ... >  -- (Note: Available in Hive 0.7.0 and later)row_format: DELIMITED [FIELDS TERMINATED BY char [ESCAPED BY char]] [COLLECTION ITEMS TERMINATED BY char][MAP KEYS TERMINATED BY char] [LINES TERMINATED BY char][NULL DEFINED AS char]   -- (Note: Available in Hive 0.13 and later)| SERDE serde_name [WITH SERDEPROPERTIES (property_name=property_value, property_name=property_value, ...)]file_format:: SEQUENCEFILE| TEXTFILE    -- (Default, depending on hive.default.fileformat configuration)| RCFILE      -- (Note: Available in Hive 0.6.0 and later)| ORC         -- (Note: Available in Hive 0.11.0 and later)| PARQUET     -- (Note: Available in Hive 0.13.0 and later)| AVRO        -- (Note: Available in Hive 0.14.0 and later)| JSONFILE    -- (Note: Available in Hive 4.0.0 and later)| INPUTFORMAT input_format_classname OUTPUTFORMAT output_format_classnamecolumn_constraint_specification:: [ PRIMARY KEY|UNIQUE|NOT NULL|DEFAULT [default_value]|CHECK  [check_expression] ENABLE|DISABLE NOVALIDATE RELY/NORELY ]default_value:: [ LITERAL|CURRENT_USER()|CURRENT_DATE()|CURRENT_TIMESTAMP()|NULL ] constraint_specification:: [, PRIMARY KEY (col_name, ...) DISABLE NOVALIDATE RELY/NORELY ][, PRIMARY KEY (col_name, ...) DISABLE NOVALIDATE RELY/NORELY ][, CONSTRAINT constraint_name FOREIGN KEY (col_name, ...) REFERENCES table_name(col_name, ...) DISABLE NOVALIDATE [, CONSTRAINT constraint_name UNIQUE (col_name, ...) DISABLE NOVALIDATE RELY/NORELY ][, CONSTRAINT constraint_name CHECK [check_expression] ENABLE|DISABLE NOVALIDATE RELY/NORELY ]

2.主键约束

其中关于主键约束的定义语句如下：

PRIMARY KEY (col_name, ...) DISABLE NOVALIDATE RELY/NORELY

在 Hive 中，可以使用 PRIMARY KEY 子句来定义主键约束，以确保表中的每行数据都具有唯一标识。主键约束要求表中的每个行都必须具有唯一的主键值，这可以通过在表中定义一个或多个列来实现。

当使用 PRIMARY KEY 子句定义主键约束时，可以使用 DISABLE NOVALIDATE 子句来禁用主键约束的验证。

CREATE TABLE my_table (id INT,name STRING,PRIMARY KEY (id) DISABLE NOVALIDATE
);

注意： 因为 Hive 目前对主键约束支持的不是很完善，现在暂不支持默认的 ENABLE 和 VALIDATE，所以定义主键约束时，「必须带上 DISABLE NOVALIDATE」，不然会报如下错误：

SemanticException [Error 10326]: Invalid Constraint syntax ENABLE/ENFORCED feature not supported yet. Please use DISABLE/NOT ENFORCED instead. (state=42000,code=1032

既然需要禁用主键约束，那么创建一个无法约束的主键意义何在呢？