How many projections per table do you recommend?
And Which column in 'projections' table, projection_name or projection_basename, counts projection?
It depends on your business requirements. One table has to have at least one super projection. You can create any projections to optimize your queries. But the additional projection will incur a system resource cost, contribute to catalog size and impact performance. But this is not a mandatory condition because we may see the cases it should create more than 8 projections to achieve the business requirements.
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You can use projection_basename column to count the projections.