Synapse cant ALTER table distribution: use CTAS and rename-swap
To change a Synapse dedicated SQL pool table's distribution or partitioning, script a CTAS rebuild: CREATE TABLE new WITH (CLUSTERED COLUMNSTORE INDEX, DISTRIBUTION = HASH(join_key)) AS SELECT * FROM old, then RENAME OBJECT old to old_bak, new to old, and drop the backup after validation. Never run it against serverless SQL pool, CTAS is unsupported there. If an agent is generating Synapse DDL, always verify the distribution choice at CREATE time since fixing it later means a full table rebuild.
Context: Microsoft Learn (CTAS docs, Synapse): you cannot change a table's distribution column with ALTER. The documented pattern is CTAS into a new table with the new DISTRIBUTION = HASH(...) / ROUND_ROBIN / REPLICATE, then RENAME OBJECT to swap the tables and drop the old one. Two more CTAS gotchas from the same page: CTAS is not supported at all in serverless SQL pool, and CTAS creates a nonpartitioned table by default even when the source was partitioned.Maintainer review
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