Table data types in Synapse SQL

Стаття
11/15/2023

In this article, you'll find recommendations for defining table data types in Synapse SQL Dedicated Pool.

Data types

Synapse SQL Dedicated Pool supports the most commonly used data types. For a list of the supported data types, see data types in the CREATE TABLE statement. For Synapse SQL Serverless please refer to article Query storage files with serverless SQL pool in Azure Synapse Analytics and How to use OPENROWSET using serverless SQL pool in Azure Synapse Analytics

Minimize row length

Minimizing the size of data types shortens the row length, which leads to better query performance. Use the smallest data type that works for your data.

Avoid defining character columns with a large default length. For example, if the longest value is 25 characters, then define your column as VARCHAR(25).
Avoid using NVARCHAR when you only need VARCHAR.
When possible, use NVARCHAR(4000) or VARCHAR(8000) instead of NVARCHAR(MAX) or VARCHAR(MAX).
Avoid using floats and decimals with 0 (zero) scale. These should be TINYINT, SMALLINT, INT or BIGINT.

Note

If you are using PolyBase external tables to load your Synapse SQL tables, the defined length of the table row cannot exceed 1 MB. When a row with variable-length data exceeds 1 MB, you can load the row with BCP, but not with PolyBase.

Identify unsupported data types

If you are migrating your database from another SQL database, you might encounter data types that are not supported in Synapse SQL. Use this query to discover unsupported data types in your existing SQL schema.

SELECT  t.[name], c.[name], c.[system_type_id], c.[user_type_id], y.[is_user_defined], y.[name]
FROM sys.tables  t
JOIN sys.columns c on t.[object_id]    = c.[object_id]
JOIN sys.types   y on c.[user_type_id] = y.[user_type_id]
WHERE y.[name] IN ('geography','geometry','hierarchyid','image','text','ntext','sql_variant','xml')
 OR  y.[is_user_defined] = 1;

Workarounds for unsupported data types

The following list shows the data types that Synapse SQL does not support and gives alternatives that you can use instead of the unsupported data types.

Unsupported data type	Workaround
geometry	varbinary
geography	varbinary
hierarchyid	nvarchar(4000)
image	varbinary
text	varchar
ntext	nvarchar
sql_variant	Split column into several strongly typed columns.
table	Convert to temporary tables or consider storing data to storage using CETAS.
timestamp	Rework code to use datetime2 and the CURRENT_TIMESTAMP function. Only constants are supported as defaults, therefore current_timestamp cannot be defined as a default constraint. If you need to migrate row version values from a timestamp typed column, then use BINARY(8) or VARBINARY(8) for NOT NULL or NULL row version values.
xml	varchar
user-defined type	Convert back to the native data type when possible.
default values	Default values support literals and constants only.

Next steps

For more information on developing tables, see Table Overview.

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