Azure SQL Data Warehouse (DW) has been improving its capabilities day-by-day. This relational database platform used by Microsoft is known to be faster and cheaper than other major cloud data warehouse solutions.<\/p>\n<\/p>\n
In this post, I will discuss a consideration for migrating databases from SQL Server on-prem or Azure SQL DB to Azure SQL Data Warehouse as it relates to global temporary tables.<\/strong><\/p>\n As you may know, with SQL Server on-prem or Azure SQL DB, local temp tables have one pound sign (#) as a part of the table\u2019s name, #Products_az for example.<\/strong>\u00a0 Local temp tables are visible only to the connection used to create it and are deleted after the connection is closed.<\/p>\n A global table will have two pound signs, ##Products_az for example.<\/strong>\u00a0 Global temp tables are visible to any connection.\u00a0 A global temp table is deleted automatically when the last connection that references it has closed.<\/p>\n You may have code in a stored procedure that creates a global temporary table in SQL Server on-prem or Azure SQL DB.\u00a0 The code to create a global temp table will execute in Azure SQL DW without error to ostensibly create a table named ##Products_az, for example.\u00a0 However, any subsequent code that queries ##Products_az will fail. Since global temp tables are not supported in Azure SQL DW, the code to create the table really created a local temp table with a name beginning with a single #.\u00a0 The \u201c##\u201d table is not created.<\/strong><\/p>\n Let\u2019s look at an example in Management Studio:<\/strong><\/p>\n Now here\u2019s where the problem comes in. At this time, Azure SQL DW only supports local tables. So, what will happen if we try to create a global temporary table in Azure SQL DW?<\/strong><\/p>\n The error is occurring because Microsoft SQL Server is still considering this a local temporary table because it looks for the first pound sign while the second pound sign is ignored and consider part of the name.<\/strong><\/p>\n This is a problem if you are trying to do a migration of hundreds of stored procedures because you will be able to batch, compile and even run without any errors. You will not run into an error until a second stored procedure or process tries to use that table which is quite a big issue.<\/p>\n It\u2019s important to keep in mind that global temporary tables are not supported in Azure SQL Data Warehouse.<\/strong><\/p>\n\n
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