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Varchar types are created with a length specifier (between 1 and 6535565535), which defines the maximum number of characters allowed in the character string. If a string value being converted/assigned to a varchar value exceeds the length specifier, the string is silently truncated. Character length is determined by the number of code points contained by the character string.

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Date types can only be converted to/from Date, Timestamp, or String types. Casting with user-specified formats is documented here.

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1. Determine what precision/scale you would like to set for the decimal column in the table.

2. For each decimal column in the table, update the column definition to the desired precision/scale using the ALTER TABLE command:

   Code Block
   sql sql
   ALTER TABLE foo CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);

   If the table is not a partitioned table, then you are done.  If the table has partitions, then go on to step 3.

3. If the table is a partitioned table, then find the list of partitions for the table:

   Code Block
   sql sql
   SHOW PARTITIONS foo;   ds=2008-04-08/hr=11 ds=2008-04-08/hr=12 ...

   
   

4. Each existing partition in the table must also have its DECIMAL column changed to add the desired precision/scale.

   This can be done with a single ALTER TABLE CHANGE COLUMN by using dynamic partitioning (available for ALTER TABLE CHANGE COLUMN in Hive 0.14 or later, with HIVE-8411):

   Code Block
   sql sql
   SET hive.exec.dynamic.partition = true;   -- hive.exec.dynamic.partition needs to be set to true to enable dynamic partitioning with ALTER PARTITION -- This will alter all existing partitions of the table - be sure you know what you are doing! ALTER TABLE foo PARTITION (ds, hr) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);

    

   
   

   Alternatively, this can be done one partition at a time using ALTER TABLE CHANGE COLUMN, by specifying one partition per statement (This is available in Hive 0.14 or later, with HIVE-7971.):

   Code Block
   sql sql
   ALTER TABLE foo PARTITION (ds='2008-04-08', hr=11) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18); ALTER TABLE foo PARTITION (ds='2008-04-08', hr=12) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18); ...

   
   

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Union types can at any one point hold exactly one of their specified data types. You can create an instance of this type using the create_union UDF:

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Missing values are represented by the special value NULL. To import data with NULL fields, check documentation of the SerDe used by the table. (The default Text Format uses LazySimpleSerDe which interprets the string \N as NULL when importing.)

Change Types

When hive.metastore.disallow.incompatible.col.type.changes is set to false, the types of columns in Metastore can be changed from any type to any other type. After such a type change, if the data can be shown correctly with the new type, the data will be displayed. Otherwise, the data will be displayed as NULL.

Allowed Implicit Conversions

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	void	boolean	tinyint	smallint	int	bigint	float	double	decimal	string	varchar	timestamp	date	binary
void to	true	true	true	true	true	true	true	true	true	true	true	true	true	true
boolean to	false	true	false	false	false	false	false	false	false	false	false	false	false	false
tinyint to	false	false	true	true	true	true	true	true	true	true	true	false	false	false
smallint to	false	false	false	true	true	true	true	true	true	true	true	false	false	false
int to	false	false	false	false	true	true	true	true	true	true	true	false	false	false
bigint to	false	false	false	false	false	true	true	true	true	true	true	false	false	false
float to	false	false	false	false	false	false	true	true	true	true	true	false	false	false
double to	false	false	false	false	false	false	false	true	true	true	true	false	false	false
decimal to	false	false	false	false	false	false	false	false	true	true	true	false	false	false
string to	false	false	false	false	false	false	false	true	true	true	true	false	false	false
varchar to	false	false	false	false	false	false	false	true	true	true	true	false	false	false
timestamp to	false	false	false	false	false	false	false	false	false	true	true	true	false	false
date to	false	false	false	false	false	false	false	false	false	true	true	false	true	false
binary to	false	false	false	false	false	false	false	false	false	false	false	false	false	true

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