Dynamic Creation of External Tables in Synapse - stored-procedures

Question

I have a json string which is the result of Get Metadata activity in data factory in the following format: {"structure": [{"name": "Id","type": "String"},{"name": "IsDeleted","type": "Boolean"},{"name": "RowVersion","type": "Byte[]"}, {"name": "ModelId","type": "String"}]
This json is showing the schema of parquet file. I pass this json along with the parquet filename and uctnow() to a stored procedure to create a table of schema for that file with the following code
CREATE OR ALTER PROCEDURE [CreateExternalTables] (
#schema NVARCHAR (MAX), #tableName NVARCHAR(MAX), #ExecTime NVARCHAR(MAX)
) AS
BEGIN
IF OBJECT_ID('tempdb..#tables_to_create', 'U') IS NOT NULL
DROP TABLE #tables_to_create
CREATE TABLE #tables_to_create (
tableName NVARCHAR (MAX),
fieldOrder NVARCHAR (MAX),
fieldName NVARCHAR (MAX),
fieldType NVARCHAR (MAX),
translatedType NVARCHAR (MAX),
executeTime NVARCHAR (MAX)
)
BEGIN
WITH Fields (fieldOrder, fieldName, fieldType) AS (
SELECT
[key] AS fieldOrder,
JSON_VALUE([value], '$.name') AS fieldName,
JSON_VALUE([value], '$.type') AS fieldType
FROM
OPENJSON(#schema)
)
INSERT INTO
#tables_to_create(
tableName,
fieldOrder,
fieldName,
fieldType,
translatedType,
executeTime
)
SELECT
#tableName,
fieldOrder,
fieldName,
fieldType,
CASE
WHEN fieldType = 'Single' THEN 'real'
WHEN fieldType = 'Boolean' THEN 'bit'
WHEN fieldType = 'Double' THEN 'float'
WHEN fieldType = 'Int64' THEN 'bigint'
ELSE NULL
END AS translatedType,
#ExecTime
FROM
Fields
END
END;
The overall setup is like below:
But I receive the following error which I'm not sure why:
What I would like to do is to create this temo table in stored procedure in order to create external tables in a automatic way.
To be precise I'm following this link to do it:
create-external-dataset
Any help is highly appreciated.
UPDATE
After solving the first problem with #wBob 's help I follow the rest of the link to create the external tables with the following which I inserted into my stored procedure:
FROM
Fields
END
Declare #sqlCommand nvarchar(max);
Declare #folderPath nvarchar(max);
SET
#sqlCommand = 'IF NOT EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N''[dbo].[' + #tableName + ']'') AND type in (N''U''))
CREATE EXTERNAL TABLE [dbo].[' + #tableName + '] ('
WHILE((SELECT COUNT(*) FROM #tables_to_create) > 0)
BEGIN
DECLARE #key int
SELECT
#key = MIN(fieldOrder)
FROM
#tables_to_create
WHERE
executeTime = #ExecTime
DECLARE #fieldName VARCHAR(50)
DECLARE #translatedType VARCHAR(50)
SELECT
#fieldName = fieldName,
#translatedType = translatedType
FROM
#tables_to_create
WHERE
fieldOrder = #key
AND executeTime = #ExecTime
SET
#sqlCommand = #sqlCommand + '
[' + #fieldName + '] [' + #translatedType + '] NULL'
DELETE FROM
#tables_to_create
WHERE
fieldOrder = #key
AND executeTime = #ExecTime
IF((SELECT COUNT(*) FROM #tables_to_create WHERE executeTime = #ExecTime) > 0)
SET
#sqlCommand = #sqlCommand + ', '
END
SET
#sqlCommand = #sqlCommand + '
)
WITH
(
LOCATION = ''/' + /main/json/ + ''',
DATA_SOURCE = DataLakeStaged,
FILE_FORMAT = StagedParquet
)'
EXEC(#sqlCommand)
END;
However I receive the following error:

Answer 1

As per the error message, queries are not supported in the conditions of WHILE statement in Azure Synapse Analytics. Dedicated SQL pools are MPP systems that have some slight differences from box-product SQL Server and Azure SQL DB and more generally, loops are a pattern that don't translate that well. You should consider creating a stored procedure that does not loop and leave any looping required to the For Each activity in Azure Data Factory (ADF) / Synapse Pipelines which can loop in parallel.
If you do require a loop, there are multiple examples of doing loops in dedicated SQL pools online, but there is a good example in the official documentation, reproduced here in the event the link moves:
-- First, create a temporary table containing a unique row number used to identify the individual statements:
CREATE TABLE #tbl
WITH
( DISTRIBUTION = ROUND_ROBIN
)
AS
SELECT ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS Sequence
, [name]
, 'UPDATE STATISTICS '+QUOTENAME([name]) AS sql_code
FROM sys.tables
;
-- Second, initialize the variables required to perform the loop:
DECLARE #nbr_statements INT = (SELECT COUNT(*) FROM #tbl)
, #i INT = 1
;
-- Now loop over statements executing them one at a time:
WHILE #i <= #nbr_statements
BEGIN
DECLARE #sql_code NVARCHAR(4000) = (SELECT sql_code FROM #tbl WHERE Sequence = #i);
EXEC sp_executesql #sql_code;
SET #i +=1;
END